Drug interactions in the elderly. How multiple drug use increases risk exponentially.

Adverse drug reactions occur more often in the elderly because of alterations in pharmacokinetics and tissue sensitivity and the increased prevalence of chronic disease. The elderly take many more prescription and nonprescription drugs than do younger people. When multiple drugs are administered, the incidence of drug interactions rises exponentially. Therefore, following the "rule of five" is recommended to minimize interaction in this vulnerable population.