Polypharmacy

Polypharmacy is defined as the concurrent use of five or more medications by a single patient, though some definitions extend this to include any unnecessary or inappropriate medication regardless of total count. The prevalence of polypharmacy increases dramatically with age: approximately 40% of adults over age 65 take five or more prescription medications, and when over-the-counter products and supplements are included, this number rises substantially. The physiological basis for polypharmacy risk lies in age-related pharmacokinetic changes that alter how the body handles medications. Absorption changes include decreased gastric acid production, reduced gastrointestinal motility, and decreased splanchnic blood flow, all of which can alter the rate and extent of oral drug absorption. Distribution is affected by changes in body composition: older adults have increased body fat (which extends the half-life of lipophilic drugs such as diazepam), decreased total body water (which increases serum concentrations of hydrophilic drugs such as digoxin), and decreased serum albumin (which increases the free fraction of highly protein-bound drugs such as warfarin and phenytoin). Hepatic metabolism declines with aging due to reduced liver mass, decreased hepatic blood...