Medication in the elderly.

Abstract

Medicine taking is common among elderly patients, especially in those over 75 years. A major problem is their increased rate of adverse drug reactions as a result of multiple drug therapy, altered pharmacokinetics, and variable response of the end organs or target tissues (pharmacodynamics). Some of these alterations have been well documented, especially alterations in excretion via the kidney. Nomograms exist which allow fairly accurate prediction of the required dosage adjustment and for some drugs measurements of their concentrations in blood can provide additional assistance in selecting an appropriate dose. However, for drugs which undergo metabolism, usually within the liver, alterations are more difficult to predict. In general, drugs like propranolol, which exhibit considerable first-pass metabolism, show a greater bioavailability in this age group and a slight prolongation of their half-lives. But other drugs, e.g. anti-pyrine, which have no significant first-pass metabolism and show a low rate of clearance from the asytemic circulation, exhibit little change in their pharmacokinetics with age. To date, studies of pharmacodynamic variation with ageing have been comparatively scant. Among those which have been documented are reduced beta-adrenoceptor sensitivity, increased effectiveness of the anticoagulant warfarin, and increased effects of a variety of benzodiazepines. Drug therapy in elderly patients should be kept simple and the number of drugs given simultaneously should be limited, and dosage may need to be reduced when a drug has a narrow therapeutic index or is excreted unchanged via the kidneys.