Panipenem/betamipron (Carbenin), a parenteral carbapenem antibiotic, is used for the treatment of severe and intractable bacterial infections caused by gram-positive and gram-negative bacteria. Because 30% of panipenem and most of the betamipron are excreted in the urine in an unchanged form, renal function is the important determinant of the dosage regimen of panipenem/betamipron. In this study, the pharmacokinetics of panipenem/betamipron were investigated in patients with end-stage renal disease (ESRD) undergoing hemodialysis treatment to establish an appropriate dose regimen. We further attempted to predict the in vivo clearance in patients undergoing hemodialysis based on the in vitro dializability. The pharmacokinetics of panipenem/betamipron were investigated in eight patients after a 1-h intravenous infusion of panipenem/betamipron (500 mg/500 mg). The in vitro extraction ratios of panipenem/betamipron through a high-flux dialyzer were obtained, and compared with those obtained in vivo. The clearances of panipenem in patients were 9.53 +/- 1.26 l/h with hemodialysis, and 2.92 +/- 0.238 l/h without hemodialysis. In contrast, those of betamipron were 4.18 +/- 0.643 l/h and 0.615 +/- 0.511 l/h, respectively. The clearance of panipenem with hemodialysis were predicted well from in vitro extraction ratios, while that of betamipron was overestimated about 1.4-fold, probably due to high plasma protein binding and the binding difference between patients and healthy subjects. After comparing the pharmacokinetic behavior of panipenem in patients with ESRD and that of a surrogate marker of efficacy, we recommend that these patients be treated with 500 mg/500 mg of panipenem/betamipron once daily, which gives a similar clinical result in a patient with normal renal function.