Critically ill patients often have complications of acute renal failure induced by severe infection or sepsis. The patients need administration of broad-spectrum antibiotics as well as continuous renal replacement therapy (CRRT). However, there is no uniform pharmacokinetics of antibiotics during the CRRT because CRRT is performed with the various combinations of dialysate flows (QD) and ultrafiltrate flows (QF). The aims of this study were to estimate the pharmacokinetics of panipenem/beta Mipron (PAPM/BP) and to determine the appropriate treatment regimens for PAPM/BP in critically ill patients undergoing CRRT. In patients with CRRT, the PAPM total clearance (PAPM CLtot) was calculated as the sum of PAPM clearance dependent on the living body and CRRT and shown as follows:PAPM CLtot (ml/min) = (1.2 CLcre + 66.5) + 0.86 (QD + QF) where CLcre is creatinine clearance. Pharmacokinetic values of PAPM were measured in 4 patients with CRRT. According to these results, the most appropriate treatment regimen regarding PAPM CLtot (ml/min) showed as follows:PAPM CLtot < 80 0.5 g every 12 hours or 1 g every 15 hoursPAPM CLtot 80 to 120 0.5 g every 8 hours or 1 g every 12 hoursPAPM CLtot 120 to 160 0.5 g every 6 hours or 1 g every 8 hours.