Influence of coadministration on the pharmacokinetics of mezlocillin and cefotaxime in healthy volunteers and in patients with renal failure.

The pharmacokinetic disposition of cefotaxime, desacetyl cefotaxime, and mezlocillin after the administration of each drug singly and in combination was examined in eight healthy volunteers and in five anuric patients with end-stage renal disease (ESRD). In the presence of ESRD, the total body clearance of cefotaxime decreased from 256.7 +/- 41.5 to 65.4 +/- 42.0 ml/min, and its elimination half-life (t1/2) increased from 1.1 to 3.6 hours as compared with healthy volunteers. Concomitant administration of mezlocillin in healthy volunteers decreased the total body clearance of cefotaxime by 42% and increased its steady-state volume of distribution. This reduction in clearance was reflected by a decrease in both renal and nonrenal clearances. In the presence of ESRD, coadministration of mezlocillin increased the t1/2 of cefotaxime to 5.8 hours. Desacetyl cefotaxime accumulated in ESRD with a prolongation of its elimination t1/2 to 18.7 hours from 1.7 hours in healthy volunteers. Desacetyl cefotaxime peak plasma concentrations occurred later with the combination regimen in the presence of ESRD. The clearance of mezlocillin was reduced and t1/2 prolonged in ESRD from 194.6 +/- 31.9 to 76.4 +/- 38.8 ml/min and 1.4 to 2.3 hours, respectively. Concomitant administration of cefotaxime did not alter the pharmacokinetics of mezlocillin. These data suggest that in the presence of normal renal function, lower doses of cefotaxime may be adequate to maintain similar cefotaxime plasma concentrations when mezlocillin is coadministered compared to when cefotaxime is given alone. Additional pharmacodynamic and clinical studies with this combination are warranted to further elucidate the clinical impact of this pharmacokinetic interaction.