Download The question: Are we over-rating the risk of low

Are we over-rating the risk of lowdose drug exposure on the
selection of resistant strains?
Pierre-Louis Toutain
National veterinary School
Toulouse
France
The question: Are we over-rating the
risk of low-dose drug exposure on the
selection of resistant strains
• But of what resistance are we
speaking?
Prevent emergence of resistance:
but of what resistance?
Target pathogens
Drug efficacy in
animal:
A vet issue
Possible
overuse of
antibiotics
Animal issue
Zoonotics
Drug
efficacy in
man
Natural
eradication
Individual issue
Commensal flora
Resistance gene
reservoir
Global ecological
problem
Risk for
permanent
colonisation
Population issue
The priorities of a sustainable
veterinary antimicrobial therapy is
related to public health issues, not to
animal health issues
The question: Are we over-rating the
risk of low-dose drug exposure on the
selection of resistant strains?
• The public health issues being critical , we have
to investigate both:
– The case of target pathogens
– The case of non-target pathogens
• Zoonotic
• Commensal flora
• And also acknowledge possible conflict of
interest
1-The case of target pathogens
Traditional hypothesis on emergence of
AMR
Concentration
CMI
Selective pressure for antibiotic concentration
lower than the MIC
Time
7
Current view for the emergence
and selection of resistance for the
target pathogen:
The selective window
Current view for the emergence and
selection of resistance
No antibiotics
Mutation rate10-8
Mutant pop
Mutation rate10-8
Wild pop
With antibiotics
Mutation rate10-8
eradication
susceptible
Mutants population
résistant
Current view for the emergence and
selection of resistance: with antibiotic
Low inoculum size
No mutants
Wild population
Usual MIC
Mutant MIC=MPC
Large inoculum
MIC<[AB]<MPC i.e.within the selective window
Large inoculum with AB
few mutants
Large inoculum
AB>MPC
Eradication of all
bacteria
10
Current view for the emergence and selection of
resistance:
The selective window
Antibiotic concentration
Growth R
Growth S
R Selection
S of R
Selective
Window
(SW)
MIC mutant=MPC
MIC
Wild population
Time in SW
MICs estimated with different inoculmum densities, relative
to that MIC at 2x105
Ciprofloxacin
Gentamicin
Linezolid
Oxacillin
Daptomycin
Vancomycin
MIC & MPC for the main veterinary quinolones
for E. coli & S. aureus
13
14
Comparative MIC and MPC values for 285 M.
haemolytica strains collected from cattle
Ceftiofur
Enrofloxacine
Florfenicol
Tilmicosine
Tulathromycine
MIC50
0.016
0.016
MIC90
0.016
0.125
MPC50
1
0.25
MPC90
2
1
MPC/MIC
125
8
2
2
1
2
8
2
4
16
4
8
>32
8
4
≈8
4
15
Consequences of a selective window
associated to an inoculum effect for a
rational treatment for veterinary
medicine
When to start a treatment?
The different uses of antibiotics in veterinary
medicine
Disease
health
Antibiotic consumption
Therapy
Metaphylaxis
(Control)
Pathogen load
Prophylaxis
(prevention)
Growth
promotion
Only a risk factor
High
Small
No
NA
The inoculum effect and Very Early
Treatment (VET)
• Tested hypothesis
– Efficacious dosage regimen is different when the
pathogen load is large, low or null
– Treatment should start as early as possible
Materials and methods
Model of pulmonary infection
Inoculation of Pasteurella
multocida
1500 CFU/lung
A strain of Pasteurella multocida isolated from the trachea of a
pig with clinical symptoms of a bacterial lung infection
Materials and methods
• Model of pulmonary infection
Inoculation of Pasteurella
multocida
1500 CFU/lung
Progression of
infection
Bacteria counts per lung
(CFU/lung)
1010
108
106
104
102
18 control mice were used to assess
the natural growth of Pasteurella
multocida in the lungs.
100
0
10
20
30
Time after infection (h)
40
50
Progression of
infection
Inoculation of Pasteurella
multocida
1500 CFU/lung
Bacteria counts per lung (CFU/lung)
Materials and methods
anorexia
lethargy
dehydration
no clinical
signs of
infection
1010
108
106
104
102
100
0
10
20
30
40
50
Time (h)
early (10h)
Administration
Late (32h)
Administration
Materials and methods
10 hours after the infection (n=14)
•A single administration of
marbofloxacin
•Two doses tested for each
group
1 mg/kg and 40 mg/kg
32 hours after the infection (n=14)
Inoculation of Pasteurella
multocida
1500 CFU/lung
1-Clinical outcome (survival)
A low early dose better than a late high dose
Marbofloxacin administrations
Pourcentages of mice alive
early
100 %
late
80
60
40
20
0
control 1 mg/kg
40 mg/kg
Marbofloxacin doses
2-Bacterial eradication
Early low dose= late high dose
Marbofloxacin administrations
% of mice with bacterial
eradication
Early
Late
100 %
80
60
40
20
0
control
1 mg/kg
40 mg/kg
Marbofloxacin doses
3-Selection of resistant target bacteria
An early 1 mg/kg marbofloxacin dose has no more impact
on resistance than a high late treatment while this low
dose is selecting resistance when administered later
% of mice with resistant
bacteria
Marbofloxacin administrations
50 %
late
Early
40
30
20
+38h
10
observation 16 hours after
marbofloxacin
administration
= 48 hours after the
infection = like early
administration
0
control
1 mg/kg 40 mg/kg
1 mg/kg
Marbofloxacin doses
40 mg/kg
+38h
Metaphylaxis vs. curative
• Pulmonary infectious model by inhalation
(P multocida)
• Amoxicillin & et cefquinome
• Treatment during the prepatent
(incubation) period (24h) vs. when
symptoms are present
M V. Vasseur, A A. Ferran, M Z. Lacroix, PL Toutain and A Bousquet-Mélou,
28
Effect of amoxicillin (clinical cure )
metaphylaxis vs. curative
Dose mg/kg
29
Effect of amoxicillin (bacteriological cure)
metaphylaxis vs. curative
Dose mg/kg
30
Effect of cefquinome (clinical cure )
metaphylaxis vs. curative
Dose mg/kg
31
Effect of cefquinome (bacteriological cure)
metaphylaxis vs. curative
Dose mg/kg
32
An early/low dose treatment is
better for bacteriological cure
than a late/high dose for three
antibiotics: marbofloxacin,
amoxicillin & cefquinome
Q:Are we over-rating the risk of low-dose
drug exposure on the selection of
resistant strains?
• A: Apparently not for the target pathogen
when an early treatment is initiated i.e when
antibiotic only a low inoculum is exposed to
an antibiotic
• But what about other non-targeted bacteria?
The question: Are we over-rating the
risk of low-dose drug exposure on the
selection of resistant strains?
• The public health issues being critical , we have to
investigate both:
– The case of target pathogens
– The case of non-target pathogens
• Zoonotics
• Commensal flora
• And acknowledge possible conflict of interest
Example of conflict of interest
• the antimicrobial treatments should not only aim at curing the
diseased animals but also at limiting the resistance on non
target flora.
Optimal dosing for treatment ≠ optimal to prevent resistance!
For AR, what are the critical
veterinary ecosystems in
terms of public health
(commensals)
The critical animal ecosystems in terms of
emergence and spreading of resistance
• Open and large ecosystems
– Digestive tract
– Skin
• Open but small ecosystem
– Respiratory tract
• Closed and small ecosystem
– Mammary gland
Bacterial load exposed to antibiotics
during a treatment
Test
tube
1µg
Infected
Lungs
1 mg
Digestive
tract
Manure
waste
Several Kg
Several tons
Food chain
Soil, plant….
Duration of exposure of bacteria exposed to
antibiotics
Manure
Digestive
Infected
Test
Sludge
tract
Lungs
tube
waste
24h
Few days
Several weeks/months
Food chain
Soil, plant….
Biophases & antibiorésistance
AB: oral route
Proximal
1-F%
G.I.T
Distal
Gut flora
•Zoonotic (salmonella, campylobacter
•commensal ( enterococcus)
Food chain
Environmental
exposure
Blood
Target biophase
Bug of vet interest
Résistance = lack of efficacy
Résistance = public health concern
Bioavailability of oral tetracyclins
• Chlortetracycline:
– Chickens:1%
– Pigs Fasted or fed: 18 to 19%
– Turkeys:6%
• Doxycycline:
– Chickens:41.3% .
– Pigs :23%
• Oxytetracycline:
– Pigs:4.8%
– Piglets, weaned, 10 weeks of age: by drench: 9%;in medicated feed for
3 days: 3.7% .
– Turkeys: Fasted: 47.6% ;. Fed: 9.4%
• Tetracycline:
– Pigs fasted:23% .
Biophases & antibiorésistance
Gastrointestinal tract
Proximal
Gut flora
•Zoonotic (salmonella, campylobacter
•commensal ( enterococcus)
Intestinal secretion
Bile
Systemic Administration
Distal
Quinolones
Macrolides
Tétracyclines
Food chain
Environment
Blood
Biophase
Target pathogen
Résistance =public health issue
Résistance = lack of efficacy
Fluoroquinolone impact on E. coli in pig intestinal flora
(From P. sanders, Anses, Fougères)
IV
•
•
•
•
IM 3 days
Before treatment : E. coli R (0.01 to 0.1%)
After IV. :Decrease of total E coli , slight increase of E. coli R (4 to 8 %)
Back to initial level
After repeated IM (3d) : Decrease below LoD E. coli (2 days), fast growth (~ 3
106 ufc/g 1 d). E. coli R followed to a slow decrease back to initial level after 12
44
days
Genotypic evaluation of ampicillin resistance:
copy of blaTEM genes per gram of feces
1 E+10
oral route fed
copies/g of feces
1 E+9
1 E+8
oral route fasted
1 E+7
intramuscular route
1 E+6
control group
1 E+5
1 E+4
0
1
2
3
days
4
5
6
7
A significant effect of route of administration on blaTEM
fecal elimination (p<0.001).
• Performance-enhancing antibiotics (old
antibiotics)
– chlortetracycline, sulfamethazine, and penicillin
(known as ASP250)]
• phylogenetic, metagenomic, and quantitative
PCR-based approaches to address the impact of
antibiotics on the swine gut microbiota
• It was shown that antibiotic resistance genes
increased in abundance and diversity in the
medicated swine microbiome despite a high
background of resistance genes in
nonmedicated swine.
• Some enriched genes, demonstrated the
potential for indirect selection of resistance to
classes of antibiotics not fed.
Ecological consequences of
the commensal flora
exposure by antibiotic
one world, one health
Vet AB
Commensal flora
Zoonotic pathogens
Gene of resistance
Transmissible genetic elements
allow antibiotic resistance genes to
spread both to commensal bacteria
and to strains that cause disease.
Resistance is contagious!
It will continue to spread even
after infection has been
cleared
Greening our AB
One world, one health
Commensal
flora
Environment
Genes of
resistance
(zoonotic pathogens)
Food chain
Commensal
flora
AMR should be viewed as a global ecological problem with
commensal flora as the turntable of the system
Selectivity of antimicrobial drugs in
veterinary medicine
Selectivity
PD
Narrow spectrum
Selective distribution of
the AB to its biophase
Innovation: PK selectivity of
antibiotics
Proximal
Distal
1-F=90%
Oral
Efflux
F=10%
IM
Gut flora
•Zoonotic (salmonella, campylobacter
•commensal ( enterococcus)
Food chain
Quinolones, macrolides
environment
Blood
Kidney
Biophase
Résistance = public health concern
Animal health
- 52
Currently no veterinary antibiotic is
selective of target pathogens and our
hypothesis was that a low dose would
be more selective than a high, regular,
dose
In vitro assessment of the selectivity
of antibiotics on the target pathogen
vs. commensal flora:
eradication of a low vs. high
inoculum size of P multocida
Selectivity of amoxicillin &
cefquinome
Using killing curves selectivity was tested using
E.coli, as a commensal bacterium in condition for
which the two tested antibiotics were able to
eradicate a low or a large inoculum of P.multocida,
Development of a selectivity index (SI)
Selectivity of amoxicillin to eradicate a low a or
a high inoculum size of P. multocida
Low: 105 CFU/mL
SI=51
High:107 CFU/mL
SI=5.54
P. Multocida (105 or 107 CFU/ml)
E coli (107 CFU/mL)
Selectivity of cefquinome to eradicate a low a
or a high inoculum size of P. multocida
Low:105 CFU/mL
SI=2.9
High:107 CFU/mL
SI=0.66
P. Multocida (105 or 107 CFU/ml)
E coli (107 CFU/mL)
I there a selective window for
the commensal flora
• All macrolides are not equals
• The normal flora is disturbed more or less
according to the pharmacokinetic profiles of
the respective macrolides.
• 85% of patients treated with
azithromycin were colonized by
macrolide-resistant organisms 6 weeks
after therapy, compared to 17% treated
with clarithromycin
Concentration ( ug/ml )
Effect of Elimination Kinetics
on Bacterial Resistance
10.00
Clarithromycin
Azithromycin
1.00
Selective Window
0.1
MIC
0.01
MAC
0.001
0
1
2
3
4
5
Weeks
Longer half-life antibiotics may create a greater window
of opportunity for the development of resistance
Guggenbichler JP, Kastner H Infect Med 14 Suppl C: 17-25 (1997)
Selective window can be longer and
delayed in the GIT
GIT/commensal
Plasma/Lung
A long half-life is desirable for convenience in
vet medicine: two possible options
Long HL
A substance
property
A formulation
property
Low clearance
High MW
Slow absorption
Large volume of
distribution
lipophilic
(flip-flop)
High clearance
hydrophilic
Likely lower
degradability
Excretion by the
GIT
Macrolides/FQ
Large diffusion
Likely higher
degradability
Excretion by the
kidney
Beta-lactams/sulfonamides
Longer half-life antibiotics may create a greater
window
of opportunity for the development of resistance
Conclusions
One size does NOT fit all!
We need to broaden the concept of selection of
resistance when devising optimal dosing strategies –
both for guidelines for future and existing antibiotics
When to finish a treatment?
• ASAP
• Should be determined in clinics
• Should be when clinical cure is actually
achieved
• Should not be a hidden prophylactic
treatment for a possible next infectious
episode
Conclusion
• For a same dose of marbofloxacin, early treatments
(10 hours after the infection) were associated to
– more frequent clinical cure
– more frequent bacteriological cure
– less frequent selection of resistant bacteria
than late treatments (32 hours after the infection)
Early administrations were more favourable than late
administrations
Normal flora: Consequences
• Treatment exerts selection on innocent bacteria
• Most of the harm done by use of a drug may be on
species OTHER than the target of treatment
• Most of the exposure of a given
species to a given drug may be
due to treatment of OTHER
infections
One world, one health
Vet AB
Hazard
Commensal
flora
Environment
Genes of
resistance
zoonotic pathogens
Food chain
Commensal
flora
AMR should be viewed as a global ecological problem with
commensal flora as the turntable of the system
New Eco-Evo drugs and strategies
should be considered in vet
medicine
Innovation: PK selectivity of antibiotics
Trapping or destruction of the antibiotic
G.I.T
Proximal
Distal
Efflux
90%
0%
Gut flora
•Zoonotic (salmonella, campylobacter
•commensal ( enterococcus)
Food chain
Quinolones, macrolides
IM
environment
Blood
Kidney
Biophase
Résistance = public health concern
Animal health
- 72
My view of an ideal antibiotic for vet medicine
High plasma clearance
Rapidly metabolized (in vivo, environment) to
inactive metabolite(s)
High renal clearance
Elimination by non-GIT route (not bile or
enterocyte efflux)
volume of distribution not too
high
Pathogens are extracellular; half-life rather short;
not too short to compensate a relatively high
clearance
High bioavailability by oral
route
To avoid to expose distal GIT to active AB
Low binding to plasma protein
Only free antibiotic is active; to reduce the possible
nominal dosage regimen and environmental load
High binding to cellulosis
To inactivate AB in large GIT
High potency
To be able to select a low dose
High PK selectivity (biophase)
To distribute only to target biophase
73
Innovation pour une voie systémique
Tractus digestif
Proximal
Distal
flore
•Zoonotiques (salmonella, campylobacter )
•commensaux ( enterococcus)
Elimination par efflux ou
biliaire=0%
Administration
Chaîne alimentaire
Environment
sang
Biophase
Pathogène visé
Elimination rénale=100%
Renal clearance of different quinolones
Drugs
Ofloxacin
Levofloxacin
Ciprofloxacin
Sparfloxacin
Grepafloxacin
Trovafloxacin
Hooper DC CID 2000;30:243-254
% of total clearance
70
65
50
13
10
5-10
Conclusions
Appropriate use of antibiotics should not
only include knowledge of the pathogen
and its susceptibility, but also the
spectrum and pharmacokinetic
properties of the respective antimicrobial
drug.
Traditional pharmacokinetic/
pharmacodynamic models
Sensitive
population
Resistant
population
S
R
Incorporating the immune response
Sensitive
population
Resistant
population
S
R
I
Immune
response
Possible pathogen dynamics
Unregulated bacterial dynamics:
Commensal bacteria
that uses body as a habitat
Regulated bacterial dynamics:
Bacteria and the immune
response settles an equilibrium