Clinical pharmacokinetics of antibacterial drugs in the elderly: implications for selection and dosage

A review of the clinical pharmacokinetics of antibiotics in the healthy elderly reveals that for most compounds a decrease occurs in renal clearance (associated with age-related decreases in renal function), as well as a prolonged half-life and increased area under the plasma concentration-time curve. These changes are amplified in the sick infected elderly. It is important that the treating physician be aware of the potential side-effects of antimicrobial agents, and whenever possible choose those which are associated with the least adverse effects. Individual patient variability, including underlying diseases and other prescribed medications, must be taken into account when dosage is selected. beta-Lactam compounds have a remarkable safety record: specifically in the elderly, their therapeutic/toxic ratio is much higher than that observed with aminoglycosides. Regimens for this class of drugs in the elderly should maintain antibiotic concentrations above the minimum inhibitory concentrations for maximum efficacy. In the treatment of elderly patients, it is suggested that dosage and interval be based on estimated or measured creatinine clearance. Usually, for drugs that are excreted primarily by the kidney (i.e. amino-glycosides, beta-lactams and quinolones), dosage intervals must be increased when there is an associated fall in creatinine clearance. The pharmacokinetic parameters suggest that as an alternative to increasing dosage interval the usual dose may be decreased, but further studies are necessary for confirmation.