Pharmacokinetics of intravenously administered cefmetazole and cefoxitin and effects of probenecid on cefmetazole elimination

Abstract

Sixteen healthy male volunteers participated in a randomized, balanced, three-way crossover study comparing the pharmacokinetics of cefmetazole, cefoxitin, and cefmetazole with probenecid pretreatment. Single 2-g doses of cefmetazole sodium and cefoxitin sodium were given intravenously as a 5-min infusion. Concentrations of cefmetazole and cefoxitin were determined by using a specific semiautomated high-performance liquid chromatographic method. Concentration-time profiles of cefmetazole and cefoxitin declined in a biexponential manner from peak levels. Compared with cefoxitin, cefmetazole had a significantly (P < 0.05) higher mean (± standard error of the mean) peak concentration in serum (290 ± 11 versus 244 ± 10 μg/ml), a longer terminal disposition half-life (1.50 ± 0.14 versus 0.81 ± 0.04 h), lower systemic clearance (111.7 ± 4.7 versus 279 ± 12 ml/min) and renal clearance (78.7 ± 4.3 versus 221 ± 14 ml/min) of intact drug, and a slightly smaller steady-state volume of distribution (10.3 ± 0.21 versus 12.8 ± 0.48 liters). Mean recoveries of cefmetazole and cefoxitin in urine were approximately 71 and 77%, respectively. Pretreatment of volunteers with probenecid (1 g orally) significantly (P < 0.05) increased concentrations of cefmetazole in serum 1 h after drug administration without significantly increasing maximum concentrations in serum. Mean areas under the concentration-time curve (466 ± 27 versus 295 ± 13 μg · h/ml) and terminal disposition half-lives (2.27 ± 0.13 versus 1.50 ± 0.14 h) of cefmetazole increased. Systemic clearance (72.1 ± 4.0 versus 111.7 ± 4.7 ml/min) and renal clearance (47.4 ± 4.0 versus 78.7 ± 4.3 ml/min) of intact antibiotic decreased. Mean recoveries (65.9 ± 3.7 versus 71.0 ± 3.2%) of intact cefmetazole in urine were not significantly (P > 0.05) different. Elimination of cefmetazole in urine was also significantly prolonged by probenecid, with substantial concentrations of cefmetazole (≥ 20 μg/ml) found in the 12- to 24-h urine collection for 14 of 16 volunteers. The results show that cefmetazole remains at clinically relevant concentrations (1 to 2 μg/ml) approximately twice as long as cefoxitin, that serum cefmetazole can be maintained longer at clinically significant concentrations with preadministration of probenecid, and that cefmetazole is partially eliminated by renal tubule secretion.