Comparative pharmacokinetics of two multiple-dose mezlocillin regimens in normal volunteers

Mezlocillin was previously reported to exhibit dose-dependent pharmacokinetics. These reports suggest that it may be possible to administer a relatively large dose at a longer interval than is usual and still achieve therapeutic concentrations in serum. In a randomized, crossover study, we compared concentrations of mezlocillin in serum after a single dose and at steady state in 12 healthy volunteers who received 4 g every 6 h and 5 g every 8 h. A slight, but statistically significant, dose-dependent effect was observed upon the area under the concentration-time curve and total body clearance. No accumulation was observed with either schedule. Although concentrations in serum were higher after the 5-g dose, the more frequent administration of the 4-g dose schedule produced serum concentrations above the MIC for susceptible bacteria for a greater portion of the day. In the absence of clear guidelines from human studies which relate serum concentrations to clinical response, the available data indicate that the more frequent dosage schedule is appropriate for severe infections.