Cefprozil is a new orally administered cephalosporin with a spectrum of in vitro activity similar to that of cefuroxime. The pharmacokinetics of cefprozil are linear relative to dose size. Gastrointestinal absorption produces maximal plasma concentrations of approximately 10 mg/L 1-2 hours after administration of an oral dose of 500 mg. Approximately 94% of the dose is absorbed, and 60%-70% is excreted in the urine as unchanged drug. The renal clearance exceeds the glomerular filtration rate, thus suggesting active tubular secretion. Administration with food or antacids produces negligible effects on the rate or extent of absorption. Kinetic disposition in the elderly is similar to that in young healthy individuals, but elimination is slightly slower in infants and children. Because renal impairment, but not hepatic dysfunction, significantly reduces the elimination of cefprozil, it is recommended that the dosage be reduced by 50% in patients whose creatinine clearance is less than 30 mL/min. Penetration of the interstitial fluid by cefprozil is excellent, with concentrations approaching those observed in the plasma. The pharmacokinetic disposition of cefprozil, coupled with its in vitro activity, supports the use of once- or twice-daily dosage regimens.