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Therapeutic Management of Burn Induced Hyperglycemia with
Insulin and Metformin
The University of Texas Medical Branch
Cell Biology Graduate Program
By: Arham Ali, MD
Mentors: Celeste C. Finnerty, PhD; David N. Herndon, MD FACS
Definitions and acronyms:
BA- Bone age
BMC- Bone mineral content
BMD- Bone mineral density
BMI- Body mass index
BSA- Body surface area
BWI- Burn wound infection
CA- Chronological age
CDC- Centers for disease control and prevention
CFU- Colony forming units
DEXA- Dual energy X-ray absorptiometry
FSR- Fractional synthetic rate (a fraction of the unbound protein pool synthesized over a unit of time)
GAM- Generalized additive mixed model
HEs- Hyperglycemic episodes
ICU- Intensive care unit
IRB- Institutional review board
ISI- Insulin sensitivity index
IU- International units
IVGTT- Intravenous glucose tolerance test
I/V- Intravenous
LBM- Lean body mass
OGTT- Oral glucose tolerance test
OR- Operating room procedure
PO- Per os (by mouth)
REE- Resting energy expenditure
RTF- Ready-to-feed
SD- Standard deviation
SEM- Standard error of the mean
S/Q- Subcutaneous
TBSA- Total body surface area
TGC- Tight glycemic control
Burn injury afflicts approximately 450,000 individuals annually in the United States. Despite efforts to
decrease incidence via implementation of public awareness campaigns and drastic improvements in living
conditions, nearly 11 million people worldwide required treatment at a major burn center or hospital in 2004.
Sustained hypermetabolism and hypercatabolism are notorious changes associated with severe burn injury.
Anchored within these pathophysiological changes is the development of hyperglycemia and insulin resistance.
These perturbations in metabolism may persist for up to three years following burn injury and are wellestablished contributors to post burn morbidity and mortality. Accordingly, the implementation of tight glycemic
control protocols in burn centers across the nation ensued. Insulin administration has been shown to attenuate
the hyperglycemic response to burn injury. Moreover, it is thought that insulin may improve auxiliary
components of hypercatabolism, indicative of insulin’s anabolic properties. However, a drawback associated
with insulin administration is the development of hypoglycemia which has led to the search for alternative
glucose modulating agents. Metformin, a well-known anti-hyperglycemic agent, has been shown to decrease
burn induced hyperglycemia in adults. Relative euglycemia was attained by use of metformin exclusive of the
adverse effects associated with insulin administration (hypoglycemia). However, the safety and efficacy of
metformin in pediatric burn patients has not been investigated. Moreover, at large doses metformin is a known
complex I inhibitor of the electron transport chain. Whether or not these alterations in mitochondrial respiration
persist at clinically relevant dosages in pediatric burn patients remains unknown. We hypothesize that insulin
attenuates hypercatabolism independent of glucose modulating effects, and that metformin will safely
attenuate hyperglycemia and associated metabolic changes in severely burn injured children. We will
test this hypothesis in two specific aims. By use of a prospective study design, in the first aim we will determine
the clinical effects of insulin vs. no insulin therapy in children with severe burn injury. Patients will be divided
into two groups: those who receive insulin to decrease serum blood glucose levels and those who did not
require insulin administration. In the second aim, we will investigate the novel use of metformin or placebo in
pediatric burn patients in a prospective, randomized control trial. This IRB-approved clinical trial will be the first
of its kind in determining safety and efficacy profiles of metformin in pediatric burn patients. Outcomes to be
collected in both aims include (but are not limited to) parameters pertaining to glucose homeostasis and insulin
resistance, body composition, metabolic changes, growth, incidence of infections and sepsis, and mortality.
Upon completion of this project, we will improve our understanding of glucose homeostasis and the therapeutic
modulators which control the hyperglycemic response to burn injury in children. If metformin is found to safely
improve clinical outcomes similar to insulin (barring hypoglycemia), we will implement the use of metformin in
our pediatric patients to alleviate hyperglycemia following burn injury.
A. Specific Aims:
Hyperglycemia and hypermetabolism are hallmarks of the pathophysiological response to burn injury.
Post burn hyperglycemia can be attributed to an increased rate of glucose release in blood,1 reduced tissue
extraction of glucose,2 and impaired insulin receptor signaling.3 This form of stress induced hyperglycemia may
be an adaptive and protective response to thermal injury. Conversely, detrimental clinical sequelae ensue
during hyperglycemia post burn in the absence of pharmacological intervention.4
Insulin is an anabolic hormone administered intravenously or by subcutaneous injection inducing
widespread systemic effects described thoroughly in the literature. In burn injured patients, insulin attenuates
the hyperglycemic response following thermal injury.5,6 Outcomes of tight glycemic control (TGC) in burn
patients have been studied in several observational and randomized control trials.7-10 Stringent control
improved body composition, decreased muscle catabolism, and reduced the incidence of sepsis, multiple
organ failure, and mortality. However, despite these improvements,11 patients on insulin therapy are at an
increased risk of hypoglycemia.7 Importantly, a single incident of severe hypoglycemia has been associated
with an increased risk of mortality in critically ill and burn injured patients.12,13 Moreover, the metabolic changes
associated with insulin resistance may persist for up to three years after initial burn injury.14 This has led to the
search for alternative glucose modulating agents in the management of burn induced hyperglycemia.
Metformin is a biguanide drug administered orally to manage hyperglycemia in patients with type II
diabetes mellitus. Metformin has been suggested as a safe alternative in the management of post burn glucose
control,15 due to a decreased incidence of hypoglycemia.16 Glucose lowering effects are attributed to a
decrease in glucose production (liver) and an increase in peripheral tissue (muscle) glucose uptake.17-19
However, in terms of safety, outcomes following the use of metformin in burn patients remain unknown. Of
major concern is lactic acidosis (which may or may not be attributed to mitochondrial complex I inhibition), a
side effect linked to medications of the biguanide drug class, but not specific to metformin. Lactic acidosis is
commonly exhibited in patients with hepatic or kidney dysfunction and tissue hypoperfusion. Nevertheless, a
causal link correlating metformin and lactic acidosis remains yet to be determined.20
We hypothesize that insulin will attenuate hypercatabolism independent of glucose modulating
effects, and that metformin will safely attenuate hyperglycemia and associated metabolic changes in
severely burned injured children. We will address the aforementioned gaps in our understanding of glucose
homeostasis in burn patients in the following specific aims in order to improve care of pediatric burn patients:
Specific Aim 1: Investigate alternative clinical effects of insulin in thermally injured children.
We will compare clinical outcomes of children with severe burn injury treated with or without insulin to maintain
blood glucose levels <180 mg/dL. By dividing groups into ‘insulin’ and ‘no insulin’, we will determine if
exogenous insulin administration attenuates hypermetabolism and/or hypercatabolism following burn injury,
independent of glucose modulating effects.
Specific Aim 2: Elucidate the clinical outcomes in the management of post burn hyperglycemia by
placebo and metformin.
We will study the use of metformin to decrease hyperglycemia in pediatric burn patients. The current standard
of care includes the administration of insulin when blood glucose levels exceed 180 mg/dL (~10.0 mmol/l). This
approach will be carried out via an IRB-approved randomized controlled trials implemented at Shriners
Hospital for Children- Galveston. Outcomes include glucose homeostasis, wound healing, insulin resistance,
hypermetabolism, body composition, organ function, incidence of infections, and mortality. By understanding
whether metformin improves clinical outcomes, we may implement a new therapeutic regimen for our patient
Our findings will help us to determine the therapeutic strategies and the mechanisms by which they act to
improve clinical outcomes. If metformin is deemed safe and effective in attaining glucose homeostasis in
pediatric burn patients, we will implement its use in our current therapeutic regimen.
B. Research Strategy
Background and Significance
Burn injury
There have been an estimated 450,000 incidents of burn injury requiring medical treatment in the United
States in 2012.21 Despite implementation of public awareness campaigns, burn injury ranks fourth amongst all
injuries.22 Two characteristic features of the pathophysiological response to severe burn injury include
hypermetabolism and hyperglycemia. Hypermetabolism is marked by increased cardiac output23,24 and resting
energy expenditure25,26 followed by detrimental changes in
body composition.24,27-29 This response to burn injury is thought
to be attributed to increased endogenous catecholamines and
cortisol. Unlike most other forms of trauma, these
derangements in metabolic homeostasis remain persistent for
up to three years post thermal injury.24,30-32
Hyperglycemia associated with burn injury
Stress-induced hyperglycemia is the result of increased
gluconeogenesis (hepatic) and decreased peripheral glucose
uptake (particularly in muscle).33-35 It is well known that burn
injury is one of the most severe forms of trauma, inciting stressinduced hyperglycemia that persists long after initial insult. The
cumulative effects of catecholamines, cortisol, and glucagon
have been postulated to contribute to the development of stress
induced hyperglycemia.36 Investigators from our institution have
previously described the relationship of these hormones and
associated down-stream effects as depicted in figure 1.3
Collectively, these hormones stimulate gluconeogenesis, foster
lipolysis and ketogenesis in the liver, and bolster insulin
resistance. The pathophysiological increase in glucose levels
serves as an energy source for glucose dependent tissues
(such as the brain). This response previously led clinicians to
Figure 1:3 Metabolic changes associated with burn
believe that stress induced hyperglycemia should be left
induced hyperglycemia.
unregulated to provide energy for increased metabolic
demands observed in critically ill patients.37 However, our laboratory has found in burn injured patients with
elevated glucose levels, a high incidence of bacteremia/fungemia and mortality.4,7 Increased incidence of
infections may be attributed to impaired immune function as a result of hyperglycemia. Elevated glucose levels
alter cytokine production in macrophages resulting in suppressed bactericidal activity in leukocytes, therefore
decreasing immune function.38,39 Similarly, immune function is compromised via immunoglobulin glycosylation
when plasma blood glucose is >220
mg/dL, resulting in decreased opsonic
activity (opsonization is a process in
which pathogens are marked for
ingestion and destruction by
phagocytes).40 Alternative to
derangements in immune function,
investigators from our institution have
found that hyperglycemia promotes
protein degradation, further enhancing
the catabolic response to burn injury.41,42
Furthermore, post burn hyperglycemia
has been associated with decreased skin
graft survival (regardless of bacterial
colonization).43 Our institution has
studied changes in glucose homeostasis
in over 970 children with burn injury and
Figure 2: Following burn injury, patients demonstrate long term fasting hyperglycemia
(A) and increased fasting insulin plasma levels (B), signifying insulin resistance (n=970).
compared them to non-burn, healthy
Bars indicate mean ± SEM. Asterisks indicate statistical significance (p<0.05) compared
children (figure 2).24 The results
to non-burned controls.
demonstrate that aberrations in glucose homeostasis (fasting hyperglycemia and hyperinsulinemia) arise
shortly after burn injury, and that insulin resistance persists for up to three years later. Sustained long term
hyperglycemia is of great concern as it can impact
morbidity and mortality. Figure 3 summarizes the clinical
consequences of hyperglycemia following burn
injury.4,9,35,40,41,43-45 Interestingly, similar outcomes are
also observed in patients with diabetes mellitus, a
condition in which patients exhibit impaired insulin
function leading to hyperglycemia if left untreated. The
subsequent consequences of hyperglycemia have led to
the implementation of stringent glucose control regimens
in intensive care units across the nation. Notably, large
fluctuations in blood glucose of thermally injured patients
serve as a precursor for sepsis and mortality.46 Currently,
a conclusive target glucose range in pediatric burn
patients has not been identified. Proposed target glucose
ranges include 80-110 mg/dL7, 90-120 mg/dL5, and 100Figure 3: Hyperglycemia following burn injury augments whole
body stress including: increased susceptibility to infections
140 mg/dL9 to name a few. Thus, reaching a consensus
attributed to decreased immune function, impaired wound healing,
on the safest glucose range for critically ill patients
and decreased muscle catabolism. BWI= Burn wound infection.
remains yet to be defined.47
Tight glycemic control
The practice of maintaining tight glycemic control (TGC) in the intensive care unit (ICU) has been a subject of
debate over the past decade. Van den Bergh and colleagues reported TGC (maintaining blood glucose <110
mg/dL) decreased incidence of infections, sepsis organ failure and mortality.48 However, others have reported
inconclusive or conflicting data, with some noting detrimental effects associated with TGC.49-51 TGC protocols
in burn injured patients have been studied in several observational and randomized controlled trials.
Decreased incidence of sepsis, multiple organ failure, and mortality have resulted from TGC.7-10 The results of
the first prospective randomized controlled intensive insulin trial in children with burn injury was performed at
our institution and published in 2010.7 Daily mean blood glucose levels in intensive insulin treated patients,
otherwise known as the TGC treatment arm (target blood glucose 80-110 mg/dL), were significantly decreased
during acute admission compared to control (target blood glucose 140-180 mg/dL), indicating improvements in
burn induced hyperglycemia (fig 4A). With regard to infections, bacteremia and fungemia were found to be
more common in patients with poor glucose control post burn.4 Of note, fungal infections are traditionally found
in patients with diabetes and/or immunocompromised states. The presence of such infections in burned
patients is indicative of hyperglycemia and immune system depression following thermal injury. Figure 4B
summarizes additional significant improvements in morbidity seen in the TGC arm which include a decreased
inflammatory response, improved lipid profile, and improved organ function as defined by the Denver2 score.7
(Denver2 is a clinical scoring system used by critical care physicians to classify organ function of the kidney,
Figure 4:7 Intensive insulin treatment (tight glycemic control) significantly decreases daily mean blood glucose post burn (4A). Intensive insulin therapy
decreased morbidity post burn (4B). Children with burn injury treated with intensive insulin therapy demonstrated significant improvements in
inflammation, lipid profile, and organ function compared to control. * indicates significant difference between intensive insulin treatment (n=49) vs.
control (n=137); P <0.05.
liver, heart, and lung.52 Organ failure may be defined when Denver2 scores exceed a value of 3.) In a similar
study, the incidence of nosocomial and ventilator associated pneumonia, and urinary tract infections were
decreased in patients on TGC therapy (by administration of insulin at high doses) compared to control.9
Despite the beneficial effects of TGC in both critically ill and burn injured patients, insulin administration often
results in an increased risk of hypoglycemia. In an effort to clarify discrepancies with TGC, a large, multicenter
prospective randomized trial lead by the NICE-SUGAR trial investigators demonstrated that patients on TGC
have a higher incidence of mortality in critically ill adults.53 Although mortality in TGC treated patients was
decreased compared to controls in the previously described trial at our institution,7 the incidence of
hypoglycemia in the TGC group was high. In fact, 26% of patients enrolled in the TGC arm observed episodes
of severe hypoglycemia (defined as blood glucose <40 mg/dL) compared to only 9% of control patients.7 It is
well known that insulin therapy is associated with a risk of inducing hypoglycemia, increasing both morbidity
and mortality.54-56 Of particular concern, even a single incident of hypoglycemia has been associated
independently with an increased risk of mortality in critically ill patients.13 Recently, our laboratory reported that
greater than one episode of hypoglycemia in children with burn injury results in increased incidence of
infections, sepsis, multi-organ failure, and mortality.57 Therefore, hypoglycemia in burn injured patients should
be avoided at all costs, making glucose control a variable to be monitored as closely as possible to ensure
optimal patient outcomes. Maintaining euglycemia in burn patients is particularly difficult as burn injury induces
a state of hypermetabolism, thereby requiring large caloric intake to prevent negative entropy. Quite often,
these patients are ordered continuous feeds through enteral feeding tubes in an attempt to maintain body
weight and attain nutritional needs. Enteral nutrition occasionally requires intermittent cessation as burn
patients undergo weekly surgical intervention. These periodic interruptions lead to a disruption of
gastrointestinal tract motility and absorption, resulting in an increased risk of hypoglycemia. Furthermore,
younger children are at a greater risk of developing hypoglycemia due to an inability to increase blood flow in
this state, limiting serum glucose availability.58,59
The high incidence of hypoglycemia has prompted discussion of the most effective glucose range in the
literature. Safe maintenance of blood glucose levels within a target range is paramount in improving morbidity.
Insulin and Metformin attenuate burn induced hyperglycemia
In severely burned patients, sub-maximal doses of insulin given during acute hospitalization has been reported
to accelerate donor site healing time, attenuate lean body mass (LBM) loss, and improve muscle protein
synthesis.7,60 In rats, insulin has been shown to improve resistance to burn wound infections.61 Intensive insulin
therapy has been shown to improve wound protein synthesis in the early postoperative period following burn
injury.62 This phenomenon can be attributed to pro-mitogenic and anti-apoptotic effects on fibroblasts and
keratinocytes by insulin downstream.63 This pathway is of great interest in burn patients as autograft skin is the
preferred method of wound coverage.64,65 However, the exogenous administration of insulin is associated with
hypoglycemia. Therefore, alternative glucose modulating pharmacological interventions have been proposed,
of which metformin has been favored due to ease of administration (tablet vs. intravenous/ subcutaneous) and
a low risk of hypoglycemia.66
Metformin (Glucophage) is an oral anti-hyperglycemic drug used widely in the management of diabetes
mellitus. A member of the biguanide drug class, metformin was introduced as a safe alternative to its
predecessor phenformin (which has since been removed from the market due to a high incidence of lactic
acidosis).67 Glucose lowering effects are attributed to a decrease in endogenous glucose production, and an
increase in glucose clearance and oxidation, likely by augmenting insulin sensitivity.18,68 These actions directly
counter derangements of glucose homeostasis in burn patients, suggesting metformin may serve as a viable
alternative in place of insulin in the management of hyperglycemia following burn injury.15,19,68 In addition to
maintaining euglycemia, metformin also decreases low density lipoprotein cholesterol and triglyceride
synthesis. This is of particular importance as triglyceridemia is independently associated with an increased risk
of morbidity following burn injury. Adverse outcomes include increased length of hospital stay, hepatomegaly,
inflammation, multiple organ failure, and mortality.69 On the grounds that metformin has been widely prescribed
to individuals with diabetes, extensive safety and efficacy profiles have been reported. It has been suggested
that there is no causal relationship between metformin and hypoglycemia, a phenomenon clearly associated
with the administration of insulin, therefore eliminating this concern.15,17,70
We have conducted several clinical studies to investigate the
effect of metformin on glucose kinetics in severely burned
adults.15,19,68 The first was conducted in 10 adult patients (age:
36±4 years) with >60% of the total body surface area (TBSA)
burns. After 8 days of metformin or placebo administration,
glucose kinetics were measured using a combination of
intravenous glucose tolerance tests (IVGTT) and isotopic
dilution using radiolabeled glucose (6,6-d2 glucose).
Measurements taken during the fasting (basal) period
demonstrated that metformin lowered endogenous glucose
production and glucose oxidation. During intravenous glucose
infusion, metformin accelerated glucose clearance, thereby
attenuating hyperglycemia (fig 5A). Serum insulin levels were
nearly three times higher in patients on metformin compared to
placebo during the glucose infusion period (fig 5B).
Endogenous insulin production was increased at this time in the
metformin group, although not enough to carry statistical
significance (fig 5C). This trend demonstrates that either
metformin signals hepatic insulin production, or that metformin
increases circulating insulin availability. This may also indicate
that metformin inhibits the breakdown of insulin by unknown
mechanisms. Hyperinsulemic euglycemic clamps are
considered the gold standard test to measure insulin
resistance/sensitivity. By use of this test, our laboratory has
shown that metformin increased glucose uptake into muscle.
Conversely, glucose kinetics were not significantly altered in the
placebo group.15 Thus, metformin attenuates hyperglycemia via
peripheral glucose uptake (muscle) and improves insulin
resistance post burn, providing strong support for our proposed
studies. The off-label use of metformin to augment burn induced
hyperglycemia in children will be the first prospective
randomized control trial of its kind. In aim 2 of my thesis, we will
investigate the aforementioned clinical outcomes in addition to
others described subsequently.
Muscle catabolism following burn injury
A major component of the hypercatabolic response to burn
injury is catabolism of skeletal muscle, a drastic response that
persists for up to at least 9 months following thermal injury.71
During starvation, ketosis and lipolysis provide energy for
metabolic utilization and to protect muscle reserves.
Conversely, following burn injury the body is unable to utilize fat
as an efficient source of energy.3 In turn, skeletal muscle is the
major fuel source following burn which leads to significant
muscle wasting, days after injury.72 Following burn injury, both muscle protein synthesis and degradation are
increased. However, a negative net balance in protein metabolism yields overall muscle loss as a result of
greater protein breakdown relative to synthesis.73 Skeletal muscle is responsible for the majority (70-80%) of
whole body insulin-stimulated glucose uptake via GLUT-4 receptors.74 Therefore, a decrease in muscle mass
may indirectly account for insulin resistance exhibited in this patient population. Excessive erosion of lean
tissue impairs physical rehabilitation post burn.75 These changes in body composition are measured clinically
by use of dual energy x-ray absorptiometry (DEXA) scans. Interestingly, both insulin and metformin have been
shown to improve derangements in body composition following burn injury. In figure 6A7 we have shown that
children on higher dosages of insulin (intensive insulin therapy) show significant improvements in bone mineral
density (BMD), body fat, lean body mass (LBM), and body mass from admission to discharge compared to
those on lower insulin dosages. Improvements in body composition and donor site wound protein synthesis62
Figure 5:15 Metformin attenuates hyperglycemia
following burn injury by increasing glucose
clearance (A) and increasing insulin availability (B).
A possible third mechanism includes increasing
endogenous insulin production marked by
increased C-peptide levels in the metformin group
(C). * P<0.05 for metformin-treated (n=5) vs.
placebo control patients (n=5).
indicate that insulin may have beneficial effects for the burn patient, independent of anti-hyperglycemic effects.
We have obtained these results (figs 4 and 5) by
investigating the effects of insulin in a doseA
dependent manner. However, in specific aim 1, we
will investigate the effects of insulin vs. no insulin
administration in addition to dose and age dependent
effects in children with severe burn injury.
In reference to muscle protein synthesis, we have
studied muscle fractional synthetic rate (FSR) using
isotopic phenylalanine (which is neither synthesized
nor secreted in muscle) as a tracer in adult burn
patients given metformin (fig 6B).19 It was found that
metformin significantly increased skeletal muscle
FSR after only one week of administration.
Improvements in body composition by insulin and
metformin may reduce the incidence of infection in
addition to improving wound healing since a 10-15%
loss of lean body mass (LBM) has been associated
with a significant increase in infections and delayed
wound healing.76 Furthermore, while the infusion of
insulin alone did not significantly affect the FSR
during baseline evaluation, co-administration of
insulin and metformin resulted in a statistically
significant increase in the FSR of muscle protein in
adult burn patients. The implications of these findings
may indicate additive or perhaps even synergistic
effects of the combined administration of insulin and
Figure 6: Change in body composition as assessed by DEXA
metformin in patients with burn injury. The combined
scans from admission to discharge in patients on intensive
administration of insulin and metformin demonstrated
insulin therapy (n=49) vs. conventional insulin therapy (control,
n=137) in children with severe burn injury. Intensive insulin
improvements in glucose control, lowered insulin
therapy significantly improved bone mineral density (BMD), body
requirements, and decreased incidence of
fat, total lean, and body mass compared to control (A).7 Adult
hypoglycemia than administration of insulin alone.77-79
burn patients (n=5) show significant improvements in skeletal
In specific aim 2 of our study we will further identify
muscle fractional synthetic rate (FSR) after 1 week of metformin
the clinical effects of the combined administration of
administration (B). *P<0.05; I= Insulin; Met= Metformin
insulin and metformin in pediatric burn patients.
Growth arrest following burn injury
Normal growth, skeletal maturation, and ultimate adult height are dependent on a number of factors including
age, sex, race, genetics, nutrition, metabolism, and overall health. As described earlier, severe burn injury
incites hypercatabolism, adversely affecting energy utilization which results in long term consequences such as
growth arrest in children. Investigators from our institution have tracked growth/height velocities in 80 children
(males and females) for three years post severe burn
injury.80 At one year post burn injury, approximately 50%
of males and 40% of females were greater than 2 SD
below expected mean height (fig 7). Furthermore,
growth arrest continued for the second year post burn in
approximately 1/3 of patients. However, by the third year
post burn, growth arrest had resolved in the majority of
children to yield a height distribution representative of
normal growth patterns. Whether or not ultimate adult
height is affected in this population remains yet to be
determined. Furthermore, it is currently unknown if
insulin, an anabolic hormone, alters growth following
Figure 7: Growth Velocity in children with Severe Burn Injury
(n=80) is significantly delayed up to two years post burn injury in
burn injury. Therefore, we will investigate the effects of
males and females. *p<0.05 compared to admission height.
insulin on growth in Aim 1 of my thesis, assessed by
height velocity and bone maturation over two years.
Lactic Acidosis
Lactic acidosis may be defined as serum lactic acid > 5 mmol/L and a blood pH of <7.35. 81 Drugs from the
biguanide drug class have been associated with causing lactic acidosis. Phenformin, the biguanine
predecessor to metformin, was removed from the market due to a high incidence of lactic acidosis. The earliest
use of metformin can been dated back to as early as 1957 in Europe.
However, it wasn’t until 1995 that the Federal Drug Administration
approved its use in the USA.16,82 Phenformin and metformin have
different molecular structures and pharmacokinetics83 thereby
moderating lactate metabolism through different pathways.84 Contrary
to phenformin, metformin is postulated to augment glucose oxidation
without significantly altering fasting lactate production in peripheral
tissue.85 Despite these stark differences, lactic acidosis has been
inappropriately linked to all biguanide drugs. Conditions associated
with lactic acidosis may be classified into five categories (fig 8). Drugs
associated with lactic acidosis include phenformin, isoniazid, and
Figure 8: Conditions associated with lactic
potassium cyanide. Genetic causes include disorders in metabolic
enzymes; pyruvate dehydrogenase deficiency, fructose 1,6
phosphatase deficiency, and glucose-6-phosphate dehydrogenase deficiency. Of particular concern in critically
ill individuals are hepatic and renal disorders which may result in either impaired metabolism or decreased
clearance of lactic acid. Burn injury impairs hepatic and renal function which may contribute to the
accumulation of lactic acid irrespective of insulin or metformin administration. For this reason we will closely
monitor patients for this severe adverse event in specific aim 2. Similarly, sepsis or conditions associated with
decreased tissue perfusion may also contribute to the development of lactic acidosis. However, it should be
noted that metformin has been extensively studied and no direct causal relationship to lactic acidosis has been
found. An outcomes study was conducted to compare patients taking metformin for one year (n=7,227) to
those receiving ‘usual care’ with sulfonylureas (n= 1,505). No incidents of lactic acidosis were observed in
either group.86 Likewise, a meta-analysis encompassing 194 trials, spanning nearly 37,000 patient-years of
metformin treatment, failed to report any incidents of lactic acidosis.87 Nonetheless, although metformin may
not directly contribute to the formation of lactic acidosis, we will diligently monitor our patients for this condition
as burn injury results in impairments in hepatic and renal function in conjunction with decreases in tissue
perfusion, both of which may independently cause lactic acidosis.
Shriners Hospitals for Children (Galveston) treats a unique pediatric burn population. As world leaders in the
management of severe burn injury in children, our faculty and ancillary staff provide the highest standard of
patient care. Patients remain in the Shriners health care system until the age of 21, and return annually for
clinical needs and to participate in research.
In this thesis, I will overview how maintenance of glucose homeostasis with insulin and/or metformin improves
patient outcomes. Although metformin has long been used to attain euglycemia in diabetic patients, this clinical
trial will be the first use of metformin in children inflicted with burn injury. By comparing standard of care
(insulin) and metformin therapeutic modalities, we will delineate similarities and differences in insulin and
metformin in regard to clinical outcomes. As insulin resistance remains a problem for our patients postdischarge, we will administer metformin for 1 year post-burn. The novel use of metformin in our pediatric burn
patients enrolled to a prospective, randomized controlled trial has far reaching implications. As leaders in burn
care, the findings of these studies will be reviewed by burn institutes across the world, many of which may
implement new therapeutic regimens accordingly. If the reduction in blood glucose is determined to be the sole
cause of improved morbidity and mortality, we will administer metformin in place of insulin to reduce the
incidence of hypoglycemia and hypoglycemic related consequences. If metformin is found to be ineffective or
detrimental to clinical care, insulin will remain the standard of care in this patient population.
Experimental Design for Specific Aim 1
Specific Aim 1: Investigate alternative clinical effects of insulin in thermally injured children.
We will compare clinical outcomes of treating children with severe burn injury with either no insulin or insulin
designed to maintain blood glucose levels <180 mg/dL. By dividing groups into insulin and no insulin, we will
determine if insulin attenuates the hypermetabolic and/or hypercatabolic response to burn injury, independent
of glucose modulating effects.
Disclaimer: Data from specific Aim 1 was presented nationally at the Southern Surgical Association, 125th
Annual Meeting, Hot Springs, Virginia in December, 2013 and published in the Journal of the American College
of Surgeons in April, 2014.88 Additionally, data from a subset of patients in this specific aim have previously
been reported in 2010. The aim of the study was to investigate the clinical effects of intensive insulin therapy in
severely burned children.7 Growth and bone maturation data was presented nationally at the Endocrine
Society, 97th Annual Meeting, San Diego, California in March, 2015. The abstract is currently in press in
Endocrine Reviews and scheduled to print in May, 2015.
Study Population: Well will investigate the effects of no insulin vs. varying dosages of insulin by reviewing data
from children with severe burn injury admitted to our institution from 1998-2013. During this period, 6,573
patients were admitted, 295 of which were not randomized to studies of various anabolic agents other than
insulin. Exclusion criteria include: presence of preexisting illnesses such as diabetes, hepatitis, HIV, AIDS, or
malignancy within the past five years; anoxic brain injury; delayed admission (burn to admit >7 days); decision
not to treat due to severity of thermal injury. After exclusion, patients were divided into those that did not
receive insulin (‘No Insulin’, n=98) and those who did receive insulin (‘Insulin’, n=145). To avoid confounds of
puberty on growth and bone maturation, inclusion criteria for this sub-analysis encompassed age 3.75-12.25
years in males and 3.75-10 years in females. Between these ages, there is a relatively stable growth rate.
Therefore, only pre-pubescent children were included for this sub-analysis.
Drug Administration: Upon admission, insulin was administered according to hospital standard sliding scales
via intravenous or subcutaneous routes to alleviate hyperglycemia. A subset of patients in the ‘Insulin’ group
received larger doses of insulin to maintain glucose control between 80-110 mg/dL. Patients in the ‘No Insulin’
group did not attain hyperglycemia severe enough to warrant clinical insulin administration. Blood glucose
levels for these patients were <180 mg/dL for the vast majority of in-patient hospital stay.
Burn care: All full-thickness burns will be excised within 24 hours of admission. We have previously reported
that early excision and wound grafting significantly improved wound closure and reduced incidence of burn
wound infections and sepsis, thereby decreasing the number of days admitted in the ICU.89,90 The majority of
any unburned skin will be harvested for autologous skin grafting using an electric dermatome (Padgett’s
Instruments, Kansas City, MO) set at 0.010 in (Zimmer Inc., Warsaw, IN). Subsequent operations will occur
approximately weekly (once donor sites have healed) until the burn wounds are 95% healed at which point
patients are discharged from the ICU. Muscle, fat, and skin biopsies for molecular, proteomic, and histologic
analyses will be obtained during surgery. With regards to wound care, autologous skin grafts will be placed
over areas debrided of burn eschar (eschar is the leather-like slough remnant of devitalized skin after burn
tissue necrosis). These areas were covered with gauze saturated with Polysporin Mycostatin ointment to
prevent infection. Skin graft donor sites will be covered with Scarlet Red (Sherwood Medical, St. Louis, MO)impregnated fine gauze to allow for quantification of wound healing time.
Glucose homeostasis: Daily mean, maximum, minimum, and 6 am glucose will be calculated according to
serial blood sample collections during the acute stay in the ICU in addition to follow up appointments in the
clinic. The number of moderate and severe hypoglycemic episodes, as defined previously, will be calculated.
Oral and/or intravenous glucose tolerance tests will be performed to assess insulin sensitivity. Briefly, an
unlabeled bolus (75 grams) of glucose is administered in fasted patients. Thereafter, plasma insulin, c-peptide,
and glucose measurements are measured every 30 minutes, over 2 hours, and are compared to baseline
levels. There are various criteria for interpreting oral glucose tolerance test results. To diagnose diabetes
mellitus, we will use guidelines set forth by the American Diabetes Association.91 Patients will be evaluated
with an OGTT at six months to determine if they should continue metformin. Metformin will be discontinued for
two weeks before the OGTT to ensure accurate results. If glucose values are above any of the values listed
below, patients will continue receiving metformin up to 12 months post burn. An abnormal OGTT will be
defined as observing any one of the following: (A) Fasting glucose levels >100 mg/dL or (B) 2 hours glucose
levels >140 mg/dL or (C) peak glucose levels >180 mg/dL after eating regardless of time. Manipulations of
these results to further assess insulin sensitivity and resistance by means of ISI HOMA and Matsuda, QUICKI,
and insulogenic index scores will be calculated as previously described.7
Hypermetabolism: The hypermetabolic response to burn injury may be assessed by measuring pulse,
respiratory rate, blood pressure, mean arterial pressure, cardiac output, and cardiac index parameters.
Metabolic response to injury and illness will be studied by steady-state REE. This provides the information
needed for optimal nutritional management. REE is measured with a Sensor Medics 2900 metabolic
measurement cart. REEs were collected during a resting state by trained respiratory therapists in an
environmentally controlled room when the patient is in a relaxed state. Subjects were tested in the supine
position using a ventilated and clear hood. REE is calculated by measuring the relationship between oxygen
consumption and carbon dioxide production. As previously mentioned, REE measurements were used to guide
nutritional management. Data gathered was compared with age predicted normal values based on the HarrisBenedict equation.
Body Composition and Growth: Anthropometric parameters will be measured weekly until discharge to track
changes in BMI. DEXA scans will be used to determine changes in whole-body, spine, leg, and arm lean body
mass. Leg scans will be subdivided at the knee into upper and lower regions to allow pre-to post-treatment
comparisons of the muscle groups. Arm regions will also be separated from whole-body measures to
determine treatment effects on these muscle groups. DEXA
measurements will be conducted as previously published.7 Bone
age will be determined using the Greulich and Pyle standard
atlas for assessment of bone age in children.92 Radiographs
were interpreted by a faculty pediatric radiologist well versed in
bone age assessment by assessment of ossification centers in
radiographic imaged of the left wrist (non-dominant hand).
Height/growth velocities were determined using standardized
growth charts from the Centers for Disease Control and
prevention (CDC) to compare rate of burn patient growth to ageappropriate, normal healthy children.93 Of note, children with a
height velocity below the 3rd percentile (>2 standard deviations)
of normal are considered to have impaired growth (fig. 9).
These children are termed those with ‘growth arrest’. Bone age
Figure 9: Growth Charts obtained from the CDC were
used to derive height velocity percentiles for boys with
and growth velocity were measured at discharge, 6, 12, 18, and
burn injury at 12 months post burn.
24 months post burn.
Inflammatory response: The inflammatory response will be assessed weekly until discharge. Cytokine
concentrations were measured using the Bio-Plex Human Cytokine 17-Plex panel with the Bio-Plex
Suspension Array System (Bio- Rad, Hercules, CA). Immunological analyses will be performed using flow
cytometry, ELISA, and western blots.
Incidence of infection, pneumonia, and sepsis: We will inspect patients daily for infection while admitted to the
ICU. Episodes of infection, pneumonia, and sepsis will be recorded. Episodes of infection will be defined as
>105 colony forming units (CFU)/gram tissue. Pneumonia will be defined by the following criteria: new
progressive and persistent infiltrate, consolidation, or cavitations, in light of the baseline evaluation for
inhalational injury on chest X-ray, along with signs of sepsis, worsening gas exchange (decreased PiO2/FiO2
ratio), increased O2, and change in the sputum (e.g., purulent or increased sputum production). Sepsis in burn
patients has been defined by the American Burn Association consensus conference in 2007.94
Overview of study assessments: Blood will be drawn at admission and once each week until discharge for
hormone measurements, cytokine profiling, and acute-phase-protein analysis. Patients will undergo metabolic
stable isotope infusions between 4 and 5 days following the first operative debridement and grafting. Additional
infusions will be performed again at 4 and 5 days after the fourth operation. During the stable isotopic studies,
skin, wound, and muscle biopsies will be performed to assess protein fractional synthetic and fractional
breakdown rates, lipolysis, and glucose production. Beginning on day 3 after the first operation, assessment of
wound healing will begin. On days 4 and 5 after the first and fourth operations, studies will be performed to
assess REE and body
composition. Indirect calorimetry
and DEXA will be performed to
assess REE, substrate utilization,
and body composition. These
studies will be repeated on days 4
and 5 following the fourth
operation to allow for assessment
of treatment-induced effects. We
will minimize patient invasion by
coordinating time points for studies
and tissue collection with
scheduled visits to the operative
Figure 10: Study schematic identifying treatment groups and summary of time points of surgery
room to address surgical needs. A
and data collection from first admission to first discharge. Note, data collection will continue after
discharge up to one year post-burn. OR= Operating room procedure; POD= Post operative day.
figurative summary of data
collection is outlined in figure 10.
Statistical Analysis:
Data were analyzed by our statistician, Clark R. Andersen, MS using R statistical software (R Core Team,
2013, version 3.0.1). Since significant differences were noted in demographic and burn injury characteristics
(table 1) a generalized additive mixed (GAM) model was used to account for nonlinear effects on the response
due age and time post-burn, and to account for repeated measures correlation by blocking on subject.
Treatment group (‘no insulin’ or ‘insulin’), age, gender, TBSA, time post-burn, inhalation injury, and number of
infections were factored into the GAM model. Log or power transformations to better approximations of
normality were utilized as appropriate, then reverse-transformed for presentation. All statistical tests assumed
a 95% level of confidence. Mortality was analyzed by an independent statistician, Kristofer Jennings, PhD,
using a Bayesian model to predict mortality. Demographics and burn injury characteristics were similar
between groups (No Insulin vs. Insulin) in the sub-analysis investigations effects of insulin on growth and bone
maturation. Therefore, the GAM model was not used in this analysis. Data with normal distribution was
analyzed using student’s t-test continuous variables, and chi-squared tests for categorical variables using
SigmaStat statistical software integrated with SigmaPlot 10 (SigmaStat, 2007 version 3.5.1).
Data in support of Specific Aim 188: A total of 295 patients were
eligible to participate in this study. Significant differences in
demographic and burn injury characteristics were noted between
groups (table 1). Generally, patients who received insulin were
older and suffered from larger and more severe (third degree)
burns with concomitant inhalation injury. However, we accounted
for these differences in the GAM statistical model, allowing us to
interpret outcomes data according to treatment group.
Table 1: Demographics and Burn Injury Characteristics.
D= Days; LOS= Length of stay; NS= Not significant;
TBSA= Total body surface area. Data presented as
means ± SD or counts (percentages).
Glycemic Control
Daily mean, maximum, and minimum blood glucose levels were
collected and analyzed. Mean glucose was significantly elevated
in Insulin vs. No Insulin groups (data not shown; p<0.01). Daily
maximum (p<0.0001) and minimum (p<0.01) glucose levels were
significantly different between groups (fig. 11). Upon further
examination, we found that blood glucose levels were directly
proportional with age, an important finding that has not been
reported in the literature. Furthermore, with each year increase in age, there was a 9% increase in the number
of hyperglycemic episodes (HEs) defined as blood glucose values >180 mg/dL (p<0.0001). This may explain
why children in the No Insulin group were significantly younger than those in the Insulin group as they were
less likely to develop hyperglycemia. Alternative determinants of hyperglycemia included percent TBSA burned
(each percent increase corresponded in a 3% increase in HEs; p<0.0001) and burn wound infections (BWI)
(each additional BWI corresponded in a 6% increase in HEs; p<0.01).
Patients in the insulin group received a daily dose of 7 ± 13
international units (IU), a daily total of 90 ± 140 IU, a cumulative
total of 1570 ± 3160 IU from ICU admission to discharge, and
were on insulin for 15 ± 16 days (means ± SD). As previously
mentioned, insulin was administered according to an insulin
sliding scale (as per hospital protocol) to maintain blood glucose
levels within the desired target range. Although insulin
administration was associated with a 35% reduction in the
Figure 11: Daily maximum and minimum blood glucose.
Patients in the no insulin group had lower maximum
blood glucose levels (P<0.0001). Patients in the insulin
group had lower minimum blood glucose measures,
placing them at increased risk for hypoglycemia
Figure 12: Insulin: Dose response effects on glucose. Daily mean blood glucose
levels generally decrease as increasing doses of insulin are administered. However,
after ~200 IU of insulin, no effect is seen, indicating either decreased utilization or
severe insulin resistance. Red bar indicates approximately 200 units of insulin
administration. IU= International units.
number of HEs (p=0.002), it also resulted in profound hypoglycemia. 52 mild hypoglycemic episodes in 43% of
patients on insulin vs. 10 episodes in 8% of patients in the No Insulin group were noted (p<0.0001). Similarly,
42 severe hypoglycemic episodes in 14% of patients on insulin vs. only 3 episodes in 2% of patients in the No
Insulin groups were observed (p<0.001). Children on insulin experienced 5.7 times more hypoglycemic
episodes compared to children in the no insulin group (p<0.0001). As expected, glucose levels varied
according to insulin dosage. Overall, blood glucose levels decreased as more insulin was administered
throughout the day up to an extent. Once patients received approximately 200 IU of exogenous insulin, further
attenuation of hyperglycemia was lost (fig.12). We speculate either decreased insulin availability or overt
insulin resistance in these patients may account for decreased efficacy. We may be able to predict which
patients require closer monitoring using this marker. Nearly identical findings were seen when we examined
cumulative insulin administration from admission to discharge (data not shown), with a marked change in
glucose levels noted at 200 IU of insulin administration, a cautionary marker of poor glucose control.
Resting Energy Expenditure
The administration of insulin resulted in a significant increase in the metabolic rate from first admission to first
discharge (figure 13). Patients treated with insulin demonstrated a 9.4% increase in REE compared to those
not treated with insulin (p=0.009). Both the amount of insulin administered during the 24 hours prior to
measuring REE in addition to the total amount administered from first admission to first discharge were directly
proportional to an increase in REE and percent predicted REE. In fact, a 1% increase in insulin administration
was associated with a 0.02% increase in REE (p=0.002). REE continued to increase significantly beyond 200
IU of insulin administration, even though no effect on glucose was observed at this dose (fig. 11). Finally, age
was also found to play a significant role in the determination of the metabolic rate. Younger children were less
likely to become hypermetabolic (p<0.0001), which corroborates with earlier findings reported from our
Figure 13: Insulin administration significantly
increased resting energy expenditure over time
(p=0.009). Data presented as means ± SEM.
Figure 14: Insulin: Dose response effects on lumbar
spine bone mineral content. Bone mineral content
increases as total insulin administration increases from
~10-200 IU (p=0.03). Red bar indicates ~200 IU of
insulin administration, at which point effect is halted.
Data presented as means ± SEM.
Body Composition
Patients on insulin therapy showed marked
improvements in body composition (assessed by DEXA scans) compared to patients not receiving insulin.
Favored outcomes were noted in: Whole body bone mineral content, lean mass, and percentage of fat mass
(p<0.001); Lumbar spine bone mineral content (p<0.05) and bone mineral density (p<0.01); and visceral
adipose tissue fat mass (p<0.05) during the first 30 days following burn injury. Many of these parameters (but
not all) remained significantly elevated up to one year post-burn injury. However, once we made adjustments
using the GAM model, only lumbar spine bone mineral content remained significantly elevated in a dose
dependent manner (p=0.03). A striking observation was noted in the dose response curve (fig. 14). Insulin
progressively increased lumbar spine bone mineral content as dosing increased from ~10-200 IU. However,
upon further administration, bone mineral content decreased, indicating a loss of effect. These results suggest
that the ability of insulin to augments body composition following severe burn injury plateaus once ~200 IU
have been administered.
Bone Maturation and Growth
Bone age and height velocities were determined in 62 pre-pubescent
children (No Insulin, n=21; Insulin, n=41). No significant differences in
terms of demographics or burn injury characteristics were noted
between groups in this sub-analysis (data not shown). Patients in the
Insulin group received on average, 800±680 IU of insulin from
admission to discharge for 14±22 days. Bone age (BA) was divided
by chronological age (CA) to obtain BA:CA ratios (normal= 0.951.05). No significant difference was noted between groups over two
years post burn injury in terms of BA:CA ratios (fig. 15). However,
insulin administration significantly improved height velocity at 12 and
18 months post burn (fig. 16A; p≤0.05). Height velocity was plotted
Figure 15: Bone Age over two years post
on growth charts provided by the CDC to identify height/growth
burn. No difference in BA:CA ratios were
velocity percentiles as described previously (fig. 9). These charts
detected. Data presented as mean ± SEM.
were derived for males and females at 12 and 24 months (data not
shown). Children were then divided into three groups based on height velocity percentiles compared to normal,
healthy children: Normal, < 2 SD (growth arrest), and >2 SD. We are most interested in identifying those
children who are <2SD from the norm as these children show stunted growth. Over twice as many children in
the No Insulin group were below 2 SD compared to children who received insulin at 12 months post burn (78
vs. 38%; p=0.02; fig. 16B). Although this pattern of growth arrest continued at 24 months post burn in the No
Insulin group, statistical significance was not found (40 vs. 21%; p=0.06; fig. 16C).
Figure 16: Insulin administration significantly improved height velocity at 12 and 18 months post burn (a). Height velocity stratification
in children at 12 (b) and 24 (c) months post burn. Children not treated with insulin were twice as likely to exhibit growth arrest for two
years following severe burn injury. Data presented as mean ± SEM *p ≤0.05
No significant difference between groups in the percentage of patients with burn wound infections, pneumonia,
or sepsis was found. However, each additional burn wound infection was associated with a 6% increase in the
number of hyperglycemic episodes (p=0.004) and significant increases in both serum creatinine and total
bilirubin (p<0.01), regardless of group. Using logistic regression no significant relationship in the species of
infection cultured (gram positive, gram negative or fungal), was found.
Notably, 17 deaths were observed in patients on insulin therapy vs. no deaths in children not receiving insulin
(p=0.001). Patients who expired were inflicted with severe burn injury (mean % TBSA burned= 80 ± 14%). The
combined effect of insulin treatment and % TBSA burned were found to be significant (p=0.02), with the
administration of insulin leading to earlier death. The hazard ratio was calculated to be approximately 1.92. We
tried to identify the mechanisms by which insulin may have been related to mortality. However, no relationship
between mortality and insulin dose (p=0.18), day post burn insulin was first received (p=0.29), or the number of
hypoglycemic episodes in patients who expired (p=0.098) was found.
The advent of intensive insulin therapy to maintain tight glycemic control in patients inflicted with burn injury
has been described in several prospective, randomized control trials.5,7,9 However, in these studies all patients
were treated with insulin and divided into groups based upon differing target blood glucose ranges. We’ve
observed that the administration of insulin to decrease blood glucose <180 mg/dL is often required, but not
universal in pediatric burn patients. Here, we have investigated two cohorts amongst pediatric burn patients:
those administered insulin to maintain relative euglycemia; and patients never treated with insulin. By
comparing these two polarizing groups, we were able to clearly examine the clinical impact of insulin on patient
outcomes following burn injury. Although the administration of insulin improved body composition and growth,
patients in this group were also noted to undergo significantly more episodes of hypoglycemia. Since
hypoglycemia has been associated with poor outcomes including increased risk of death, the benefits of insulin
therapy do not outweigh the risks. Therefore, the implementation of tight glycemic protocols at our institution
and others have been abrogated. Furthermore, once patients have received ~200 IU of exogenous insulin,
further administration may prove to be futile. Perhaps administering ~200 IU of insulin may serve as a
surrogate marker of patients with severe illness, and this finding requires further review. We will continue to
investigate the effects of other glucose modulating agents to attenuate burn induced hyperglycemia. As
outlined in specific aim 2, metformin may emerge to be a safe and effective alternative, either in combination
with insulin or as standalone therapy.
Specific Aim 2- Elucidate the clinical outcomes in the management of post burn hyperglycemia by
insulin and metformin. By directly comparing endpoints in clinical care between treatment groups, we will
have a better understanding of whether insulin or metformin more significantly improves whole-body and organ
function post burn.
Experimental Design for Specific Aim 2:
Study population and patient accrual:
Patients between 10–18 years of age with greater than 20% TBSA burns will be enrolled into an institutional
review board (IRB) -approved, prospective randomized control trial. Exclusion criteria include: Age <10 or >18
years, presence of preexisting illnesses such as diabetes, hepatitis, HIV, AIDS, or malignancy within the past
five years; prevalent or acquired allergy to metformin; impaired hepatic or renal function; anoxic brain injury;
delayed admission (burn to admit >7 days); decision not to treat due to severity of thermal injury.
Insulin and metformin administration:
On admission, all patients will be resuscitated with Ringer's Lactate solution to account for the massive fluid
loss and third spacing exhibited by patients following burn injury. Immediately after admission, patients or their
legal guardian will be asked for consent to participate in the study. After obtaining consent, we will randomize
patients into one of the following two groups: (1) Control- Patients will receive a placebo twice a day in addition
to standard burn care for up to one year following burn injury. Conventional insulin therapy will be given to
maintain blood glucose levels between 140-180 mg/dL. (2) Metformin- Patients will receive 250-500 mg twice a
day in addition to standard burn care to maintain blood glucose levels between 80-140 mg/dL. Drug
administration will be initiated as soon as possible after enrollment and will be continued until patients are
discharged from the intensive care unit (ICU). After discharge, patients on placebo or metformin will continue to
receive the respective drug twice a day for up to one year post burn injury. Drugs will be administered for at
least 14 days. Insulin will be given intravenously or subcutaneously and metformin via a duodenal feeding tube
(in-patient) or per os (out-patient). As metformin is started in the ICU shortly after admission, it is expected that
a stable dose will be obtained before discharge. In addition it is common for patients to remain in the
community for 6-12 weeks post burn injury as they participate in an exercise program (both treatment groups)
to improve mobility and strength lost following burn injury. Before discharge home, patients will have an OGTT
performed. During the 6-12 week time period in the community, glycemic control will continue to be monitored.
Patients and their families will receive education and training during this period regarding study drug
administration, glucose monitoring, urine monitoring and safety reporting. By the time the family returns to their
home, they will be knowledgeable about all aspects of metformin, when to hold a dose for glucose <70 mg/dL
and when to contact a physician if needed. If glucose is above 180 mg/dL after discharge home, the patient will
be instructed to contact their family physician. In addition they will be asked to call the hospital to speak to a
physician to provide further instructions.
In the control group, insulin infusion will be started if blood glucose exceeds 180 mg/dl. The infusion will be
adjusted according to a sliding scale to maintain blood glucose levels to 140–180 mg/dl. These glucose ranges
have been selected to comply with guidelines set forth by the Surviving Sepsis Campaign.96 Insulin dose will
be based on measurements of blood glucose from arterial blood performed at 15-120 minute intervals using a
glucose analyzer (AccuCheck Advantage, Roche Diagnostics, Indianapolis, IN). The dose of insulin will be
adjusted according to a standardized insulin sliding scale.
We will administer metformin to decrease blood glucose to 80-140 mg/dL. Our preliminary data show that the
dose of metformin needed to decrease glucose levels to this range in adults is 850 mg every 8 hours. In
children, the dose will be based on body surface area (BSA), taking into account both the height and weight of
the child (dose will be ~250–500 mg every 12 hours). All patients will receive enteral feeding of Vivonex
Ready-to-Feed (RTF) (Novartis, Minneapolis, MN) at a rate of 1.4 times their REE (determined by indirect
calorimetry), beginning the second day after admission. One liter of Vivonex RTF provides 1,000 kcal
(composition: 50 g of proteins, 175 g of carbohydrates, 12 g of fat) and multiple essential vitamins and
electrolytes. All patients will receive the same caloric amount to avoid differences in nutrition and metabolism
between groups.
When patients go to the operating room for surgical procedures, metformin will be discontinued the morning of
surgery. Patients will be reassessed following surgery for renal function and lactic acid accumulation. After
these parameters are determined to be within normal ranges, metformin will be restarted. For patients that
receive contrast studies with iodine materials, metformin will be discontinued for 48 hours following the
procedure, assessment will be done for renal failure and lactic acidosis between 24-48 hours, metformin will be
restarted after renal function and lactic levels are determined to be normal. While in the ICU, metformin will be
held for any lactic acid levels outside normal limits. Acidosis may ensue following burn injury due to periods of
sepsis or ventilator status. Lactic acidosis has been described previously. If this occurs, metformin will be
discontinued until the condition resolves. At that time the physician and/or the safety committee will re-evaluate
the patient’s condition and if the lactic acid level has returned to normal, metformin may be restarted. During
the time the subject is an inpatient or an outpatient, if there is a single episode of a lactic acid value above
normal limits, metformin will be temporarily suspended. Re-administration of metformin will occur only once
lactic acid levels return to normal and a physician has reviewed the events leading to the incident.
Data supporting specific aim 2
We have successfully enrolled 33 patients into a prospective, randomized control trial to investigate the effects
of metformin (n=13) vs. control/placebo (n=20). No significant differences in patient demographics and burn
injury characteristics were found between groups (table 3).
Glycemic Control
Metformin was initiated on average six days after burn injury in the treatment group. Metformin significantly
reduced mean blood glucose levels for the first two weeks following burn injury compared to control/placebo
(fig. 17). The intended reduction in glucose was not accompanied with an increased incidence of hypoglycemic
episodes. In fact, children on metformin did not experience hypoglycemia at all. Of the 2472 recorded glucose
Table 3: Demographics and Burn Injury Characteristics. D=
Days; LOS= Length of stay; TBSA= Total body surface area.
Data presented as means ± SD or counts (percentages).
Figure 17: Weekly mean blood glucose. Metformin
significantly attenuated hyperglycemia following burn
injury in children compared to placebo/control. Data
presented as mean ± SEM; *p<0.05.
measurements, a single measurement of 60 mg/dL was
recorded and found to be the absolute minimum in all
children treated with metformin. For reference, mild or severe hypoglycemia is diagnosed when plasma blood
glucose levels are <60 mg/dL or <40 mg/dL respectively. Conversely, there were seven minor and three major
episodes of hypoglycemia in 25 and 20% of children in the control group respectively. This data suggests that
metformin can be used to attenuate burn induced hyperglycemia in children without risking the development of
hypoglycemia. Furthermore, the data corroborates the response to metformin in burned adults we have
previously reported.15 Hypoglycemia in the control group is attributed to significantly larger exogenous insulin
administration. Patients in the control group required over three times the amount of exogenous insulin
administration in order to maintain relative euglycemia (blood glucose <180 mg/dL) compared to children on
metformin (table 4). Small increases in insulin sensitivity assessed by oral glucose tolerance tests (OGTT)
were noted in the metformin group: Insulin sensitivity index (ISI) Matsuda scores were higher in metformin
patients compared to control/placebo (5.0 ± 3.3
vs. 3.8 ± 3.3; p=0.13), as were ISI HOMA (0.58 ±
0.64 vs. 0.40 ± 0.28; p=0.31), and QUICKI scores
(0.34 ± 0.04 vs. 0.32 ± 0.04; p=0.31). Currently,
these differences are not significant between
groups. However, Freemark et al. reported
Table 4: Exogenous insulin administration. Metformin significantly decreased
significant improvements in ISI HOMA and
the need for insulin administration to maintain blood glucose levels <180
QUICKI scores in obese adolescents randomized
mg/dL. IU- International units. Data represented as medians ± SD.
to metformin treatment for 6 months,97 a response we anticipate to observe as the total number of patients
enrolled in the clinical trial increases. We then compared differences in fasting glucose levels from OGTTs
taken close to admission to those performed approximately four months post burn. Metformin significantly
decreased fasting glucose levels compared to control, indicating marked improvements in long term glucose
homeostasis (-20 ± 14 vs. -4 ± 11 mg/dL; p=0.04). It is postulated that metformin inhibits gluconeogenesis
and/or glycogenolysis, thereby reducing fasting blood glucose levels.85,98
Resting Energy Expenditure
At our institute, daily caloric needs and dietary intake are
based on data measured from resting energy expenditure
(REE)/indirect calorimetry. Metformin significantly reduced
percent predicted REE by hospital discharge compared to
control/placebo (116±36 vs. 157±37 %, p=0.04; fig. 18). An
alternative method of measuring REE is to divide actual REE
by weight. This method also showed a significant reduction in
the hypermetabolic state by hospital discharge in children
treated with metformin vs. control (33±14 vs. 48±10
Kcal/day/kg; p=0.03). We hypothesize this reduction in REE to
be attributed to reduced insulin requirements in metformin vs
control patients (table 4). In specific aim 1, we found that
Figure 18: Hypermetabolism. Metformin significantly
insulin administration was associated with a 9% increase in
reduced percent predicted resting energy expenditure
(REE) by hospital discharge compared to control.
REE following burn injury in children (fig. 13). Therefore, with
Data presented as mean ± SEM; *p<0.05.
reduced insulin requirements to maintain relative euglycemia,
metformin indirectly attenuates hypermetabolism by hospital discharge.
Safety (lactic acidosis)
One of the major outcomes of this trial was to identify whether or not metformin is safe to administer in children
(age 10-18 years) following severe burn injury. As discussed previously, metformin has been linked to the
development of lactic acidosis. Therefore, we closely monitored for this adverse effect. To date, there have
been no incidents of lactic acidosis (defined as blood pH <7.25 and lactic acid >2.1 mmol/L) while on
metformin as assessed by serial measurements of lactic acid and pH in arterial blood gases (fig. 19).
In this preliminary study, we
investigated the effects of
metformin on the hyperglycemic
response to severe burn injury in
children. To the best of our
knowledge, this is the first
prospective, randomized control
trial of its kind in this population.
Our findings indicate that
metformin is a safe and effective
Figure 19: Lactic acidosis. Lactic acid (a) and pH (b) were similar between groups.
Metformin did not cause lactic acidosis in children with severe burn injury. Red bar
alternative to insulin
indicates maximum normal level. Green bars indicate normal range. Data presented as
administration in this population.
mean ± SEM.
Metformin significantly reduced
mean blood glucose levels, insulin requirements, and hypermetabolism compared to control/placebo during
acute hospitalization. Most importantly, metformin was not related to the advent of hypoglycemia or lactic
acidosis. Long term effects remain yet to be determined. We will continue to monitor these patients for 1 year
following burn injury, and thereafter for safety and efficacy.
We would like to address a few limitations in our specific aims and findings thereof. In specific aim 2, loss to
follow up may potentially hinder our ability to measure long term variables as we have designed to follow up
with these patients for at least 1 year post burn injury. However, burn injured patients are unique in that
treatment includes serial surgical operations in order to obtain cosmetic and motor function. Following severe
burn injury, patients typically undergo 10-20 surgical procedures within 5 years. Therefore, our patients return
periodically, at which time we collect data to meet our proposed protocol. Lack of compliance may be another
drawback seen with even the best designed clinical trials. Before discharge from the ICU, we thoroughly
explain to patients and their families the benefits of maintaining blood glucose within a particular range and the
consequences which may occur if euglycemia is not achieved. During follow up visits in our outpatient clinic,
we will identify causes for reduced compliance and all efforts will be made to correct any misinterpretations.
Parents are asked to document drug administration on a day to day basis in a log book which is examined
during follow up. This provides an audit to assure proper drug dosing has been achieved. In the event that
metformin fails to attenuate hyperglycemia or adverse events are noted, the dosage may be titrated
accordingly. Temporary or permanent cessation of the drug may be implemented if needed. We have noted
the current metformin dose of 500 mg given twice a day, although safe, may not be the most effective dose. No
significant differences were noted in mean blood glucose levels between groups at 3 and 4 weeks post burn
which prompts us to believe that a higher dose may be required to further attenuate hyperglycemia. As this is
the first clinical trial approved to administer metformin to children with severe burn injury, we are very cautious
and elected a conservative dosing approach. Since no serious adverse events were noted in the treatment
group, we may increase the dose to 850-1000 mg administered twice a day. These dosages have been
reported to be safe and effective in children and adolescents with obesity,99-103, type II diabetes mellitus,104,105
and in girls with hyperandrogenism106 and polycystic ovarian syndrome.107 Furthermore, long term
accumulation of metformin in blood and tissue over 1 year of administration may have profound effects in the
outcomes measured. We h look forward to enrolling more children to this prospective, randomized control
clinical trial.
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