3
antihypertensive agents or two central-nervous-system
depressants, are generally not included. Effects expected from
the mechanism of a drug’s action, such as that of potassium on
digitalis glycosides or calcium on calcium-entry blockers, and
useful antagonist effects, such as that between a poison and an
antidote, are not listed. Most interactions of drugs with foods,
beverages, or other nutrients are not included, but foods
interacting with monoamine oxidase inhibitors are included.
Mechanisms of Interaction—Genetic differences can affect
drug metabolism and interactions. Drugs can interact by
changing the metabolism of other drugs, either through
inhibition or induction of any of several hepatic enzyme
activities or through alterations in hepatic blood flow; by altering
the binding of other drugs to plasma proteins or tissue
receptors; by altering the distribution of drugs to active receptor
sites; by delaying or enhancing excretion; or by causing additive
or synergistic effects.
Recommendations—Monitoring is most important when one of
the interacting drugs is stopped or started. Some experienced
clinicians may prefer to monitor the patient’s clinical status
rather than follow serum concentration of drugs.
Important Notice: The Medical Letter Drug Interactions
Program reports interactions occurring in people, which
can be documented primarily by published reports.
These may not include interactions mentioned in other
sources, such as the manufacturer’s package insert,
which are extrapolated from animal studies or interac-
tions reported for related drugs.
Introduction
