Geriatric Prescribing: Beers Criteria Logic

The AGS Beers Criteria identifies potentially inappropriate medications (PIMs) in older adults based on the pharmacological principle that age-related physiological changes fundamentally alter drug safety profiles. Renal clearance decline (GFR loss of ~1 mL/min/year after age 40) causes accumulation of renally eliminated drugs: glyburide's active metabolites cause prolonged hypoglycemia lasting 24-72 hours; gabapentin accumulates causing somnolence and falls; dabigatran reaches toxic levels increasing hemorrhage risk. Hepatic phase I metabolism (CYP450 oxidation) decreases with aging while phase II reactions (conjugation) are relatively preserved, making drugs dependent on oxidative metabolism (diazepam, chlordiazepoxide) particularly dangerous — diazepam half-life increases from 20 hours at age 20 to over 90 hours at age 80. Age-related reduction in cholinergic neurons makes older adults exquisitely sensitive to anticholinergic medications: muscarinic blockade produces a dose-dependent cognitive impairment spectrum from mild inattention to frank delirium. The Anticholinergic Cognitive Burden (ACB) Scale assigns scores of 1-3 to medications based on anticholinergic potency; cumulative scores of 3 or greater predict cognitive decline and delirium. Beers Criteria categories address: (1) medications to avoid regardless of condition, (2) drug-disease interactions (e.g., anticholinergics in...