Pharmacokinetics of ciprofloxacin in the elderly: increased oral bioavailability and reduced renal clearance.

The pharmacokinetics of ciprofloxacin was studied after single intravenous and oral doses of 250 mg and during and after a five-day oral regimen of 500 mg twice daily in eight young (22-34 years) and eight elderly (63-76 years), healthy male volunteers. The absolute bioavailability of an oral dose was greater in the elderly than in the young subjects at both 250 mg (72 versus 58%; p less than 0.05) and 500 mg (79 versus 63%; p less than 0.05). Distribution was unaffected by age. The physiological aging of the kidneys resulted in a reduced renal clearance, while no significant changes in non-renal clearance, total clearance and terminal half-life were found in the elderly. The age-related increase in the bioavailability of ciprofloxacin, whether due to facilitated absorption and/or reduced first-pass elimination, is a hitherto unique finding for antibiotics. As a consequence, reduction of orally administered doses of ciprofloxacin should be considered for elderly patients.