Clinical Pharmacology of Mezlocillin

Mezlocillin is a new broad-spectrum semisynthetic penicillin that has shown encouraging in vitro activity against the infecting organisms most likely to cause mortality and morbidity in cancer patients receiving chemotherapy. The serum clearances and urine recoveries of mezlocillin, ampicillin, and carbenicillin were compared after the intravenous administration of single 3-g doses. The peak mean serum concentrations of mezlocillin and carbenicillin were 269 and 278 μg/ml, respectively, whereas the peak ampicillin level was lower at 167 μg/ml. The terminal half-life of mezlocillin, 66 min, was not significantly different from those of ampicillin and carbencillin (63 and 77 min, respectively). Recoveries of mezlocillin, ampicillin, and carbenicillin from urine over 6-h periods after drug dosage were 45, 61, and 80%, respectively. A further study in 11 cancer patients examined serum maintenance levels of mezlocillin when 3-g doses were given intravenously every 4 h for at least 7 consecutive days. After 3 days of therapy, the mean serum concentrations were maintained above 50 μg/ml. Although therapeutic efficacy was not an objective of this study, all of three documented bacterial infections were cured, and no serious toxicity was encountered.