Cefixime is a new oral cephalosporin with in vitro activity similar to that of third-generation cephalosporins. Renal excretion accounts for only 40% of systemic clearance of cefixime, suggesting that biliary excretion of the drug may be significant. This study was designed to determine to what extent nonrenal clearance of cefixime is due to biliary excretion of the parent compound. In an isolated perfused rabbit liver model, biliary excretion of cefixime was very low, with only 0.28 +/- 0.15% of a single 10 mg dose injected in the system being recovered in the bile after three hours perfusion. The liver biotransformation rate for cefixime was found to be 16.2%. These results are in striking contrast with those obtained in human studies. Cefixime levels in duodenal juice aspirates collected over four hours following an intravenous injection of 200 mg cefixime in six healthy volunteers were at least fivefold concomitant serum levels. Studies of bile collected by external biliary drainage during 24 hours following an oral dose of 200 mg cefixime in ten cholecystectomized patients showed that the Cmax was 56.9 +/- 70 mg/l, i.e., 25-fold the serum Cmax (2.3 +/- 0.85 mg/l). The bile AUC/serum AUC ratio was 20.4 +/- 20.3. Mean bile level of cefixime was still as high as 4.3 +/- 3.7 mg/l 20 hours after dosing. The amount of cefixime excreted in the bile over 24 hours was 10.0 +/- 12.3 mg i.e., 5% of the dose administered. Twenty-four hour renal excretion of cefixime was 53.3 +/- 26.2 mg.(ABSTRACT TRUNCATED AT 250 WORDS)