Nonlinear pharmacokinetics of DQ‐2556, a new 3‐quaternary ammonium cephalosporin antibiotic, in rats caused by non‐michaelis—menten type, dose‐dependent renal clearance

□ The pharmacokinetics and its dose dependency of a new cephalosporin, DQ-2556, were studied in the rat and rabbit. The pharmacokinetics of the compound In the rat was linear up to a dose of 300 mg/kg; however, at a dose of 1200 mg/kg, renal clearance decreased dramatically and the normalized area under the blood concentration-time curve increased remarkably. On the other hand, there were no dose-dependent changes in tissue/serum concentration ratios, serum protein binding, red cell binding, and the distribution of DQ-2556. In the rabbit, the pharmacokinetics of DQ-2556 was linear even up to a dose of 1200 mg/kg and no unusual pharmacokinetic behavior was observed. The renal clearance experiments demonstrated that DQ-2556 is excreted by glomerular filtration. It was also shown that the glomerular filtration rate (GFR) remained constant up to a dose of 1000 mg/kg of DQ-2556 in the rat, whereas the GFR decreased by 95.1 % at a dose of 1200 mg/kg. The coincidence of dose relationship and species difference in the disorder of GFR and renal toxicity suggests that the change of pharmacokinetics of DQ- 2556 was caused by its renal toxic effects at very high dose.