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Prescribing for the elderly |
Polypharmacy
The higher prevalence of disease in the elderly means that elderly people often take multiple drugs. The risk of adverse drug effects and interactions is therefore higher. Be aware that patients may be prescribed drugs from several sources (multiple doctors, multiple hospitals). This is further complicated by the possibility of the person taking self-prescribed over-the-counter medications, drugs for a previous illness, or even drugs prescribed for another person; the elderly are well known as hoarders of medicines. Domiciliary medication management review may be necessary to confirm exactly what is being taken
Pharmacokinetics
The most important effect of ageing is reduction in renal function, resulting in reduced elimination of renally excreted drugs (eg. digoxin) and active drug metabolites (eg. metabolites of allopurinol and pethidine). Dosages of these drugs should be reduced in the elderly. Failure to make appropriate dose alterations probably explains, in part, the increased incidence of adverse drug reactions in the elderly.
Renal function may be significantly impaired in the elderly despite apparently normal serum creatinine levels; therefore calculation of creatinine clearance may be necessary to estimate renal function. This is especially important when prescribing renally excreted drugs with a narrow therapeutic index (eg. digoxin) or nephrotoxic drugs (eg. aminoglycosides).
Acute illness (eg. myocardial infarction, urinary tract infection) can lead to a rapid decrease in renal function and renal clearance of drugs, and a person stabilised on a renally cleared drug with a narrow therapeutic index may rapidly develop toxicity. Monitor renal function and adjust chronic drug treatment appropriately in elderly patients with acute disease.
John Hayman is the division’s MMR facilitator.
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