are predictable and other times they are not and may be unrelated to the dosage.
Some side effects are desirable and others are undesirable.
A severe undesirable side effect is referred to as an adverse reaction that
occurs unintentionally when a normal dose of the drug is given to a patient. For
example, an adverse reaction might be anaphylaxis (cardiovascular collapse)
Some adverse reactions are predictable by age and weight of the patient.
Young children and the elderly are highly responsive to medications because of
an immature or decline in hepatic and renal function. Body mass also influences
the distribution and concentration of a drug. The dosage must be adjusted in pro-
portion to body weight or body surface area.
Drug effects can also be related to other factors. These include:
Gender.Women typically are smaller than men and have a different propor-
tion of fat and water which affects absorption and distribution of the drug.
Environment.Cold, heat, sensory deprivation or overload, and oxygen depriva-
tion in high altitude create environmental factors that might interact with a drug.
Time of administration.A drug might be influenced by the presence or
absence of food in the patient’s gastrointestinal tract or by the patient’s cortio-
costeroid secretion rhythm. In addition, circadian cycle, urinary excretion pat-
tern, fluid intake, and drug metabolizing enzyme rhythms all might influence a
drug’s effect.
Pathologic state.A drug can react differently if the patient is experiencing
pain, anxiety, circulatory distress, or hepatic and/or renal dysfunction.
Idiosyncracy.This is an abnormal response that is unpredictable and unex-
plainable that could result from the patient overresponding or underresponding
to the drug or the drug having an effect that is different from what is expected.
Tolerance.The patient has a decreased physiologic response after repeated
administration of the drug. This is common with tobacco, opium alkaloids,
nitrites, and ethyl alcohol. The dosage must be increased to achieve the pharma-
ceutical response.
Drug dependence.This can be either a physical or psychological dependency.
With a physical dependency, the patient experiences an intense physical distur-
bance when the drug is withdrawn. With psychological dependency, the patient
develops an emotional reliance on the drug.
Drug interaction.The administration of one drug increases or decreases the
pharmaceutical response of a previously administered drug.
Synergism.A more desirable pharmaceutical response is achieved through the
interaction of two drugs that are administered.
Potentiation.Concurrent administration of two drugs increases the pharma-
ceutical response of one of those drugs.
Toxic effect.This occurs when the administered drug exceeds the therapeutic
range through an overdose or by the drug accumulating in the patient.
CHAPTER 2 Drug Action and Drug Interactions^37