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The renal excretory mechanism of cefmenoxime in rabbits was compared with that of 6 other cephalosporins (cefotaxime, deacetylcefotaxime, cefotiam, cefazolin, cephaloridine, and cefsulodin). The clearance ratios (Cf-Drug/CInulin=CRf) of cefmenoxime (337) and cefazolin (73) were considerably higher than those of the 5 other cephalosporins (0.9-20). When p-amino-hippurate (PAH) was administered concurrently with each of the cephalosporins, the CRf values of the cephalosporins except for cefsulodin were significantly decreased. These findings indicate that cefmenoxime and the 5 other cephalosporins except cefsulodin are actively incorporated in the proximal tubular cells and secreted into the tubular lumen. In the case of cefotiam and cefsulodin, glomerular filtration tended to exceed urinary excretion with highest dose of PAH (40 mg/kg/minute), suggesting the possibility of tubular reabsorption of these drugs. On the other hand, glomerular filtration of cefmenoxime and the 4 other cephalosporins did not exceed urinary excretion. The drug concentration ratio of the cortex to medulla indicated that the tubular cell level of cefmenoxime was lower than, higher than, and similar to those of cephaloridine, cefotaxime, and the remaining cephalosporins, respectively. These results demonstrate that the renal excretory mechanisms of cefmenoxime is similar to that of cefazolin but not to that of the remaining cephalosporins.

The renal excretory mechanism of cefmenoxime was compared with those of 6 other cephalosporins (cefotaxime, deacetylcefotaxime, cefotiam, cefazolin, cephaloridine and cefsulodin) in rats and rabbits. In rats, renal clearance (Cf-Drug: corrected for serum protein binding) of cefmenoxime (4.06 ml/minute) was lower than that of cefazolin, similar to that of cefotiam, and higher than those of cefotaxime, deacetylcefotaxime, cephaloridine, and cefsulodin. In rabbits, the value for cefmenoxime (2,519 ml/minute) was markedly higher than those for the other drugs. If the clearance ratio (Cf-Drug/CInulin = CRf) is more than unity, tubular secretion of a drug is indicated. In rats, the tubular secretion of cefmenoxime equalled the glomerular filtration (CRf = 2.17). The tubular secretion of cefmenoxime was lower than that of cefazolin but similar to that of cefotiam. None of the other cephalosporins seemed to be secreted significantly. In rabbits, a large amount of cefmenoxime was secreted (CRf = 208). The tubular secretion was larger than those of the other cephalosporins. All the drugs except cefsulodin showed significant tubular secretion. A species difference was observed in the CRf of the cephalosporins: the values were generally higher in rabbits than in rats.