Pharmacokinetics and prescribing in the elderly.

The use of prescribed medication in general is higher in the elderly than in the young and it is possible that existing patterns of antimicrobial agent prescribing may predispose to suboptimal response, certain adverse drug reactions (ADR) and the emergence of resistant strains of organisms. Age is an important variable affecting the pharmacokinetics of drugs, including many antimicrobials. Changes which may affect Cmax/MIC ratios and/or the time above MIC include reduced first-pass metabolism, altered distribution volume, reduced binding to albumin, reduced metabolic biotransformation and reduced renal elimination. Application of a knowledge of antimicrobial agent pharmacokinetic changes with age and their implications for response may enable more precise determination of dose regimens for older patients, which is probably desirable for the prevention of both ADR and bacterial resistance.