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Focus on
PHARMACOLOGY
ESSENTIALS FOR HEALTH PROFESSIONALS
CHAPTER
1
Introduction to
Pharmacology
General Principles
“To administer a drug safely, one must
know its usual dose frequency, route of
administration, indications,
contraindications, significant adverse
reactions, and major drug interactions.”
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacology
• Pharmacology: the study of drugs and
their actions and effects in body
systems
• Pharmacodynamics: the study of
biochemical and physiologic drug
effects, and the mechanisms of drug
action
• Pharmacokinetics: the study of drug
absorption, distribution, metabolism,
and excretion
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Other Pharmacologic Terms
• Pharmacognosy: the study of drugs
derived from herbal or natural sources
• Pharmacotherapeutics: the study of
how drugs are best used and which
drug is appropriate for a specific
disease
• Toxicology: the study of poisons and
poisonings
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics
• Absorption, distribution, metabolism,
and excretion of drugs are related to:
– Concentration of drug
– Drug’s chemical by-products in various
body sites
– Time required for drug concentrations to
develop or change
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Figure 1-1 The four processes of pharmacokinetics (that is, movement) are absorption, metabolism,
distribution, and excretion.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacodynamics
• Describes all matters concerned with
pharmacologic actions of a drug,
including:
– Therapeutic effects (effects that are meant
to treat a disease or disorder)
– Adverse effects (harmful effects)
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Dose-Effect Relationship
• Pharmacokinetics and
pharmacodynamics determine the
dose-effect relationship:
– Relationship between dose of a drug that
produces harmful effects and severity of
effects on client
– Body’s response to a drug or toxic agent
increases as overall exposure to substance
increases
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Figure 1-2A The dose-effect relationship. Along the x-axis is the drug dose, which
increases from left to right. Along the y-axis is the maximum response for each drug
(%). (A) These curves show drug potency. Drug A’s curve is to the left of drug B’s curve,
which indicates that drug A has a higher potency. This means that a smaller dose of drug
A will produce the same effect as a larger dose of drug B.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Figure 1-2B (B) These curves show drug efficacy (or effectiveness). Drug A reaches a
maximum response of 100% at the same dose as drug B, which reaches a maximum
response of about 60%. Therefore, drug A’s efficacy (or effectiveness) is greater than
that of drug B.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Mechanisms of Drug Action
• Drugs work by altering normal cell and
tissue function.
• Specific groups of drugs have affinity
(attractive force) for specific target
cells, known as receptors.
• Binding of drugs to a particular receptor
type produces pharmacologic effect—
either agonist or antagonist actions.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Agonists and Antagonists
• Two types of chemical substances bind
to receptors:
– Agonists: drugs that bind to receptors and
produce stimulatory responses that are
similar to that produced by endogenous
chemicals
– Antagonists: drugs that prevent agonists
from binding to receptors, thus blocking
their effects
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Receptor Selectivity
• Some receptors have subtypes, for
which certain chemicals have some
selectivity.
– For example, beta (β)-adrenoreceptors
have two subtypes, β1 and β2.
– The drug propranolol (Inderal) is an
antagonist at both β1 and β2, whereas
atenolol (Tenormin) is selective for β1.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Drug Half-Life
• Half-life (t1/2): time taken for the drug’s
blood or plasma concentration to
decrease from full to one-half (50%)
– The longer the half-life, the longer the drug
remains in the body
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Figure 1-3 Plasma concentration of a drug versus time. The onset of action occurs at 2
hours; the duration of action is 6 hours; peak plasma concentration is 10 mcg/mL; and
the time to reach peak drug effect is 5 hours.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Factors Affecting Drug Action
• Age
– Affects metabolic rates, requiring dosage
adjustments
• Gender
– Responses to drugs sometimes differ
• Body weight
– Dosages may require adjusting for body
weight and body surface area
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Factors Affecting Drug Action
• Diurnal rhythms
– Intensity of response to drug may be
affected by when it is given
• Disease
– Dosages may need to be adjusted in
persons with kidney or liver disease
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Drug Elimination in
Elderly Patients
• Acute or chronic diseases that affect
liver architecture or function also affect
hepatic metabolism of some drugs
• Elderly patients may therefore have
markedly affected drug elimination and
require dosage adjustment
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Absorption
• Absorption: movement of drug into
systemic circulation
– Depends on drug’s ability to cross cell
membranes and resist presystemic
metabolism (enzymes in GI tract begin to
break down drug before it is absorbed)
– Presystemic metabolism affects drug’s
bioavailability—amount of drug that
reaches systemic circulation intact and its
speed
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Factors That Affect Absorption
• Acidity of the stomach
• Physiochemical properties: dissolution,
solubility, thermodynamics
• Presence of food in stomach or
intestine
• Routes of administration: PO, IV, IM,
subcutaneous, transdermal, sublingual,
buccal, rectal, vaginal
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Distribution
• Distribution: passage of agent through
blood or lymph to various body sites
• Many drugs are bound to circulating
proteins, affecting their ability to bind
to receptors; cross tissue membranes;
and be distributed, metabolized, and
excreted.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Metabolism
• Most drug metabolism occurs in the
liver.
• First-pass effect (metabolism of drug
by liver enzymes before it reaches
systemic circulation) influences
metabolism.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Metabolism
• Substances that are absorbed across
the intestinal wall enter blood vessels
and are carried directly to the liver
(hepatic portal circulation).
• End-products of metabolism are
metabolites.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Figure 1-4 First-pass effect. Oral drugs are absorbed through the intestinal wall and
enter the hepatic portal circulation. They are taken directly to the liver for metabolism
before reaching the heart and circulating throughout the body.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Biotransformation
• Biotransformation is the conversion of
drugs in four stages:
– Oxidation: combining with oxygen
– Reduction: gaining electrons
– Hydrolysis: cleaving into simpler
compounds
– Conjugation: combining with glucuronic or
sulfuric acid, terminating biologic activity
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Excretion
• The main route of excretion is via the
kidneys.
• Kidney diseases can prolong the
duration of drug action.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Pharmacokinetics: Excretion
• Other routes of excretion include:
– Lungs
– Breast milk
– Sweat, tears, urine, feces
– Bile
– Saliva
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Other Pharmacologic Principles
• Toxicity: refers to drug’s ability to
poison the body
• Overdose: dose of drug that causes
harm
• Adverse drug reaction (ADR): any
response to drug that is noxious,
unintended, and occurs at doses
normally used for prophylaxis,
diagnosis, or therapy
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Other Pharmacologic Principles
• Side effect: an unintended drug effect;
this can be beneficial
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Drug Interactions
• Occur when the effects of one drug are
altered by those of another drug
• Occasionally, the effects of both drugs
are altered.
• Drug interactions usually result in an
adverse drug reaction, though some
interactions may be beneficial.
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Idiosyncratic Reactions
• Idiosyncratic reaction: a unique,
strange, or unpredicted reaction to a
drug
• Allergic reaction: hypersensitivity to
drug that occurs after previous
exposure to similar or same drug, and
develops rapidly after reexposure
• Anaphylactic shock: idiosyncratic,
sudden, and life-threatening allergic
reaction
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Allergy History
• Ask all patients if they have a history of
allergies, such as hay fever, rashes or
asthma, or have had unusual reactions
to any drugs taken orally or by
injection
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Table 1-1
Allergic Drug Reactions
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Tolerance
• Tolerance: development of resistance
to drug’s effects, such that dose must
be continually raised to elicit desired
response
• Drugs that commonly produce
tolerance are:
– Opiates
– Barbiturates
– Tobacco
– Nitrates
– Alcohol
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Other Drug Effects
• Cumulative effect: occurs when body
cannot completely metabolize and
excrete one drug dose before next dose
is given
• Synergism: occurs when combined
action of two or more agents produces
a greater effect than expected from
agents acting separately
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini
Other Drug Effects
• Potentiation: a greater effect than
expected caused from additive
properties of two or more drugs
Focus on Pharmacology: Essentials for Health Professionals, Second Edition
Jahangir Moini