ADVERSE DRUG REACTIONS IN THE ELDERLY
The relation between
the number of drugs taken and the incidence of adverse drug reactions has been
well documented. In long-term care facilities, in which a high percentage of
the population is elderly, the average number of prescriptions per patient varies
between 6 and 8. Studies have shown that the percentage of patients with
adverse reactions increases from about 10% when a single drug is being taken to
nearly 100% when 10 drugs are taken. Thus, it may be expected that about half
of patients in long-term care facilities will have recognized or unrecognized
reactions at some time. Patients living at home may see several differ-ent
practitioners for different conditions and accumulate multiple prescriptions
for drugs with overlapping actions. It is useful to conduct a “brown bag”
analysis in such patients. The brown bag analysis consists of asking the
patient to bring to the practitioner a bag containing all the medications, supplements, vitamins, etc, that he or she is
currently taking. Some prescriptions will be found to be duplicates, others
unnecessary. The total number of medica-tions taken can often be reduced by
30–50%.
The overall incidence
of drug reactions in geriatric patients is estimated to be at least twice that
in the younger population. Reasons for this high incidence undoubtedly include
errors in prescribing on the part of the practitioner and errors in drug usage
by the patient. Practitioner errors sometimes occur because the physician does
not appreciate the importance of changes in phar-macokinetics with age and
age-related diseases. Some errors occur because the practitioner is unaware of
incompatible drugs pre-scribed by other practitioners for the same patient. For
example, cimetidine, an H2-blocking drug heavily prescribed (or recom-mended in its
over-the-counter form) to the elderly, causes a much higher incidence of
untoward effects (eg, confusion, slurred speech) in the geriatric population
than in younger patients. It also inhibits the hepatic metabolism of many
drugs, including phenytoin, warfarin, β blockers, and other agents. A patient who has
been taking one of the latter agents without untoward effect may develop
markedly elevated blood levels and severe toxicity if cimetidine is added to
the regimen without adjustment of dosage of the other drugs.
Patient errors may
result from nonadherence for reasons described below. In addition, they often
result from use of nonpre-scription drugs taken without the knowledge of the
physician. As noted, many over-the-counter agents and herbal medications
contain “hidden ingredients” with potent pharmacologic effects. For example,
many antihistamines have significant sedative effects and are inherently more
hazardous in patients with impaired cognitive function. Similarly, their
antimus-carinic action may precipitate urinary retention in geriatric men or
glaucoma in patients with a narrow anterior chamber angle. If the patient is
also taking a metabolism inhibitor such as cimetidine, the probability of an
adverse reaction is greatly increased. A patient taking an herbal medication
containing gingko is more likely to experience bleeding while taking low doses
of aspirin.
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