Phase II metabolism, the conjugation of drugs, is not significantly affected by aging. Drug elimination is mainly influenced by renal function. The age-associated decrease in renal function, which results in decreased creatinine clearance, necessitates lower maintenance doses of renally excreted drugs in elderly patients. The effect of aging on target-organ responsiveness to medications is less well established. However, decreased beta-receptor sensitivity and increased sensitivity to opiates is well established.
Many elderly patients are also more sensitive to the adverse effects of anticholinergic drugs.
The prevention of iatrogenic illness from inappropriate drug prescribing begins with an understanding of the rational use of medications in elderly patients. Consensus criteria for appropriate drug prescribing may prove useful. In general, prescribing the fewest medications at the lowest needed dosage is a rational approach to the prevention of iatrogenic illness. Knowing the pharmacology of prescribed drugs and the age-related alterations in drug disposition and tissue sensitivity and using lower than standard doses of most drugs when the therapeutic dose is uncertain should help physicians avoid adverse drug reactions. Computerized hospital information systems, clinical pharmacists, and lists of inappropriate drugs may help reduce the incidence of adverse drug effects.