Prescribing medicines for older patients

Prescribing medicines for older patients is more challenging than prescribing for younger adults as there is less room for error. The physiological changes associated with ageing have important consequences for the pharmacokinetics of drugs. Water-soluble drugs are cleared more slowly with increasing age by virtue of reduced functioning nephrons. In contrast, lipid-soluble drugs are cleared more slowly via hepatic metabolism and are distributed into a larger volume of distribution as a result of the physiological reduction in body water. This results in two separate mechanisms via which the elimination half-life is prolonged. These changes need to be considered together with the changes in pharmacodynamics seen with increasing age. In addition, a number of characteristic changes are seen in the presence of organ disease such as cardiac failure or chronic kidney disease. Finally, the prevalence of frailty rises dramatically with increasing age and is associated with changes over and above those seen as a result of age alone. Reductions in protein binding and consequent increases in volume of distribution and elimination half-life, as well as reduced hepatic enzyme activity are seen in frail elderly patients.