Download Factors Affecting Drug Activity

Factors Affecting
Drug Activity
Chapter 11
Human Variability

Differences in age, weight, genetics
and gender as well as pregnancy are
among the significant factors that
influence the differences in responses
to medication among different
people.

Drug distribution, metabolism, and
excretion are quite different in the
neonate and infant than in the adult
because their organ systems are not
fully developed.
Human Variability

Children metabolize certain drugs more rapidly than
adults.

The elderly typically consume more drugs than other
age groups.

The elderly also experience more physiological change
that significantly affects drug action.

Genetic differences can cause different types &
amounts of proteins to be produced in the body,
causing a difference in drug action.
Adverse Drug Reactions

Drugs generally produce a mixture of therapeutic
(desired) and adverse (undesired) effects.

Adverse drug reaction can be any symptom in any
disease process & involve any organ.

Almost any drug in any dose can produce an allergic or
hypersensitive reaction in a patient.

Anaphylactic shock (example: bee sting) is a potentially
fatal hypersensitive reaction.
Adverse Drug Reactions

Common GI tract adverse reactions include:
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Nausea
Vomiting
Constipation
Diarrhea
Teratogenicity is the ability of a substance to cause
abnormal fetal development when given to pregnant
women.
Adverse Drug Reactions

Nephrotoxicity: the ability of a
substance to cause harm to the
kidneys.

Carcinogenicity: the ability of a
substance to cause cancer.
Drug-Drug Interactions

The administration of more than one drug at a
time to a patient can cause drug-drug
interactions.

Drug-drug interactions can affect the disposition
of one or more drugs and result in the increase
or decrease of therapeutic effects or adverse
effects.
Drug-Drug Interactions (Terms)

Additive effects: occur when two drugs with similar
pharmacological actions result in an effect equal to the
sum of the individual effects.

Synergism: two drugs with similar pharmacological
actions produce greater effects than the sum of the
individual effects.

Potentiation: when one drug with no inherent activity
of its own increases the activity of another drug that
produces an effect.
Drug-Drug Interactions (Terms)

Antidote : blocks or reduces toxic effects of a drug.

Displacement: a drug bound to a plasma protein is
removed when another drug of greater binding potential
binds to the same protein.

Inhibition: a drug blocks the activity of metabolic
enzymes in the liver.

Induction: a drug that causes more metabolic enzymes to
be produced, thus increasing metabolic activity.
Time Course of Drug Interactions

The time it takes for drug-drug interactions to
occur can vary substantially.

Some interactions occur immediately, others may
take weeks.

Knowing the time-course of an interaction allows
quick identification & treatment of potential
interactions.
Drug-Diet Interactions

Dietary intakes and pattern vary widely among
individuals and can contribute to variability in
the disposition of drugs.

Some foods contain substances that react with
certain drugs.

Example: foods containing tyramine can react
with MAO ( monoamine oxidase) inhibitors.
Disease States

The disposition and effect of some drugs can be
inhibited by the presence of diseases other than
the one for which a drug is used.

Hepatic, cardiovascular, renal and endocrine
disease all increase the variability in drug response.

Example: renal disease has been correlated with
decreased renal excretion of many drugs.
Disease States

Acute Viral Hepatitis: an inflammatory
condition of the liver caused by viruses.

The effects are less than cirrhosis, but long term
exposure progresses into a chronic disease state.

The chronic disease has the same characteristics
as cirrhosis; which eventually causes fatal liver
damage.
Disease States

Hypothyroidism: a condition in which thyroid
hormone secretions are below normal (under
active thyroid).

Hyperthyroidism: a condition in which thyroid
hormone secretions are above normal (over
active thyroid).