Prescribing medicines for older patients

Prescribing medicines for older patients is more challenging than prescribing for younger adults. The physiological changes and co-morbidities associated with ageing alter both the pharmacokinetic handling of and pharmacodynamic response to drugs. Water-soluble drugs are cleared more slowly with increasing age by virtue of a reduced number of functioning nephrons. Lipid-soluble drugs are cleared more slowly via hepatic metabolism and are distributed into a larger volume as a result of the physiological reduction in the proportion of body water. There can also be changes in the response to drugs because of altered sensitivity of target organs such as the heart, kidney and brain. These changes affect the likely therapeutic response and risk of adverse effects and require careful consideration by prescribers when selecting drugs and dosage regimens. 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. Awareness of appropriate prescribing guidelines is key to successful management of such patients.