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Chapter 30
Pharmacology for the Orthopaedic
Physical Therapist
Overview
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Pharmacology is the broad area of study
that deals with how chemical substances
affect living tissue on a molecular level and
how drugs affect specific patient populations
The Guide to Physical Therapist Practice
identifies clinical pharmacology as an
essential component of appropriate patient
monitoring, modality delivery, and
communication among medical professionals
Drug Development and
Regulation
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It is the responsibility of the Food and
Drug Administration (FDA) to direct
the drug development process and
give approval for marketing a new
drug or approving a new use for an
older drug.
FDA approval involves a 4-step process
FDA 4-step Approval
Process
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Phase 1: The safety assessment study
Phase II: The drug effectiveness study
Phase III: Larger study including many
more subjects with the disease than in the
previous phase, and a much longer duration
for the testing
Phase IV: Begins when the drug is approved
for public use and includes monitoring of
the drug for safety on the real-life
conditions in large numbers of patients
Controlled Substances
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Control substances are drugs classified
according to their potential for abuse.
These drugs are regulated under the
Controlled Substances Act, which
classifies these compounds into
schedules from I to V
Controlled Substances
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Schedules I-II:
– I: Drugs that are available only for research.
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They have a high abuse potential, leading to
dependence without any accepted medical use.
Examples include heroine, and LSD
– II: Drugs that also have a high abuse potential
but that have accepted medical uses.
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Examples include amphetamines, morphine, oxycodone
Controlled Substances
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Schedules III-IV
– III: Drugs with lower abuse potential but may
still be abused and can result in some physical
and psychological dependence.
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Examples include mild to moderately strong opioids,
barbiturates, and steroids.
– IV: less of an abuse potential.
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No more than five refills within 6 months are allowed
within the same prescription.
Examples include opioids, benzodiazepines, and some
stimulants.
Controlled Substances
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Schedule V
– These drugs have the lowest abuse
potential and are often available without
prescription.
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Examples include various cold and cough
medicines containing codeine.
Drug Classifications
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Specific categories that provide an
explanation of the overall pharmacological
action on a specific disease process
Pharmacological action, e.g., arterial
vasodilators and anesthetics
Molecular action, e.g., calcium channel
blockers
Chemical makeup or the source of the drug,
e.g., atropine and penicillin
Pharmacodynamics
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The drug’s mode of action
– Potency
– Efficacy
– Tolerance
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The indications for use of a drug
The drug’s safety profile
The site of action
Drug Receptors
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Receptors come in various forms and
can be located inside the nucleus of a
cell, in the cytoplasm, or on the
surface of the cell
A number of receptors are recognized
and are classified as being either
membrane-bound or intracellular
Autonomic Nervous
System Receptors
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No discussion about drug receptor sites
would be complete without mention of the
impact of the autonomic nervous system
(ANS) has on drug delivery.
Drugs that are used in the treatment of
autonomic dysfunction can be subdivided
into 3 groups:
– Cholinergic
– Muscurinic
– Adrenergic
Pharmacokinetics
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The study of the physicochemical factors
involved as the body absorbs, distributes,
metabolizes, and eliminates a drug.
– Bioavailability--refers to the fraction or
percentage of active medication that reaches the
systemic circulation following administration by
any route.
– The volume of distribution (Vd) is used to
indicate how a systemic dose of the medication
is ultimately dispersed throughout the body.
– Clearance is the rate at which the active form of
the drug is removed or eliminated from the body
Transport of Drugs Across
Cell Membranes
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When given by most routes (excluding
intravenously), a drug must traverse semipermeable cell membranes (biological
barrier) at several locations before reaching
the systemic circulation.
– Drugs may cross a biologic barrier by diffusion
through the water filled channels or specialized
ion channels, passive diffusion through the lipid
membrane, carrier-mediated processes that
include a facilitated diffusion, active transport, or
pinocytosis
Drug Absorption and
Routes of Administration
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Absorption is the process by which a
drug is made available to the body
fluids that distribute the drug to the
organ systems.
– A prerequisite to absorption is drug
dissolution. The size, shape of the drug’s
molecule, and its solubility in water or
lipids determine the ability of specific
drug absorption.
Drug Absorption and
Routes of Administration
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The primary routes of administration
include:
–
–
–
–
–
–
–
Oral
Buccal
Sublingual
Rectal
Parenteral
Topical
Inhalational
Bioavailability
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In pharmacology, the term
bioavailability is used to describe the
rate and extent of a therapeutically
active drug that reaches the systemic
circulation and is available at the site
of action
Controlled-Release Drug
Forms
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Controlled-release dosage forms are
designed to reduce dosing frequency
and to reduce fluctuation in plasma
drug concentration, providing a more
uniform therapeutic effect.
– Less frequent dosing is more convenient
and may improve patient compliance.
The Effects of Exercise on
Pharmacokinetics
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The effects of exercise on drug
distribution are complex and is
dependent on factors that pertain to
the characteristics of each drug as well
as exercise-related factors such as
exercise intensity, mode, and duration
The Effects of Physical
Agents on
Pharmacokinetics
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Similar to exercise, physical therapy
modalities have the potential to alter
the pharmacokinetics of locally and
systemically administered drugs,
primarily by affecting blood flow and
tissue kinetic and metabolic activity
Distribution of Drugs
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The distribution of a drug refers to the
movement or transport of a drug to
the site of action.
Metabolism of Drugs
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Metabolism refers to the process of
transforming a drug into a compound
that can be excreted
Drug Elimination
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Drugs are eliminated from the body by a
variety of routes including elimination in
fluids (urine, breast milk, saliva, tears, and
sweat), through the GI tract in the feces,
and expelled in exhaled air through the
lungs.
– The kidney is the primary organ for excretion of
drugs that have been inactivated by the liver
Drug Half-life
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The half-life is the rate at which a drug
disappears from the body, through
metabolism, excretion, or a
combination.
– It is the amount of time required for half
of the drug that is in the body to be
eliminated.
Musculoskeletal
Pharmacology
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Opioid Analgesics
– Most of the narcotics used in medicine
are referred to as opioids, as they are
derived directly from opium or are
synthetic opiates
Non-Opioid Analgesics
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Nonopioid analgesics comprise a
heterogeneous class of drugs including
the salicyclates (aspirin and diflunisal),
paraaminophenol derivatives (primarily
acetaminophen), and the nonsteroidal
anti-inflammatory drugs (NSAIDs),
such as ibuprofen, Naprosyn, Motrin,
and many others.
Nonsteroidal
antiinflammatory
drugs (NSAIDs)
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NSAIDs are distinguished from true steroid
agents such as cortisone, prednisone, and
from the opiate-derived analgesics
NSAIDs also seem to promote the
inhibition of the release of cyclooxygenase1 (COX-1) and cyclooxygenase-2 (COX-2)
and the synthesis of prostaglandins at an
injury site
Corticosteroids
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Corticosteroids are natural antiinflammatory hormones produced by the
adrenal glands under the control of the
hypothalamus.
Synthetic corticosteroids (cortisone,
dexamethasone) are commonly used to
treat a range of immunological and
inflammatory musculoskeletal conditions.
Skeletal Muscle Relaxants
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Skeletal muscle relaxants are thought
to act by decreasing muscle tone
without causing impairment in motor
function and by acting centrally to
depress polysynaptic reflexes.
Micronutrients
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Vitamins and minerals are essential for
efficient nutrient metabolism and
numerous bodily functions affecting
functional activity and athletic
performance
Vitamins
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Fat-soluble vitamins:
– Include vitamins A, D, E, and K.
– After being absorbed by the intestinal tract,
these vitamins are stored in the liver and fatty
tissues
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Water-soluble vitamins:
– Include the B complex, vitamin C, biotin, choline,
and folacin (folic acid).
– Water-soluble vitamins are not stored in the
body in any significant amount, which
significantly reduces the incidences of toxicity,
but requires that they be included in the diet on
a daily basis
Minerals
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Minerals, like vitamins, are important
nutrients found in foods. The main
difference is that vitamins are organic
substances (meaning that they contain
the element carbon) and minerals are
inorganic substances