Background: As the elderly population increases, so, too, does the number of multimorbid patients and the risk of polypharmacy. The consequences include drug interactions, undesired side effects of medication, health impairment, and the need for hospital- ization. 5-10% of hospital admissions among the elderly are attributable to undesired side effects of medication.
Methods: This review is based on publications retrieved by a selective search in PubMed and the Cochrane Library that employed the search terms "drug interaction," "undesired side effect," "polypharmacy," "pharmacokinetics," and "pharmacody- namics."
Results: Elderly patients are particularly at risk of polypharmacy, both because of the prevalence of multimorbidity in old age and because of physicians' uncritical implementation of guidelines. The more drugs a person takes, the greater the risk of drug interactions and undesired side effects. Age-associated changes in pharmacokinetics and pharmacodynamics elevate this risk as well. Physicians prescribing drugs for elderly patients need to know about the drugs' catabolic pathways, protein binding, and inductive and inhibitory effects on cytochrome P450 in order to avoid drug interactions and polypharmacy.
Conclusion: Multiple aids and instruments are available to ensure practical and reasonable drug monitoring, so that the risks of drug interactions and undesired side effects can be detected early and avoided.