Charles A. Cefalu, MD

ABSTRACT: Age-related changes that affect drug distribution, such as increased total body fat, decreased muscle mass, and decreased total body water, necessitate reduction in the dosage of water- and lipid-soluble agents. Because creatinine clearance declines with age, the dosage of agents that are excreted primarily by the kidney must also be lowered to prevent toxicity. Examples include aminoglycosides, fluoroquinolones, penicillins, procainamide, lithium, angiotensin-converting enzyme inhibitors, and digoxin. A good rule of thumb to follow until creatinine clearance can be calculated is to reduce the total dose by half in frail elderly persons or in those with established renal disease. Anticholinergic agents should be used with caution because they are associated with urinary retention, heart block, constipation, dry mouth, blurred vision, sedation, and acute or chronic confusion in elderly patients.