Moxalactam and piperacillin: a study of in vitro characteristics and pharmacokinetics in cancer patients.

We evaluated the microbiologic characteristics including MIC determinations, synergy plate assays and serum bactericidal activity for two regimens being examined as empiric antibiotic therapy for febrile granulocytopenic cancer patients. The regimens consisted of moxalactam (4 g.i.v. q12h) plus piperacillin (75 mg/kg i.v. q6h) or moxalactam (as above) plus amikacin (levels adjusted to one hour post-infusion levels of 25 mg/l and troughs of 6-8 mg/l). Detailed pharmacokinetics were ascertained for the beta lactams. All drugs were active against a panel of 11 strains each of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. The pharmacokinetic profile showed serum levels sufficient to provide good antimicrobial activity throughout the dosing interval. Both regimens displayed synergistic or partially synergistic activity in the main for the test organisms; moxalactam plus piperacillin produced good results against S. aureus and P. aeruginosa. In the serum bactericidal assays, the moxalactam-piperacillin combination produced significantly higher mean titers at both peak and trough when compared to the moxalactam-amikacin regimen. This may be because moxalactam acts as a beta lactamase inhibitor for both staphylococcal beta lactamase, as well as the Sabath-Abraham Id type beta lactamase carried by P. aeruginosa (among others). Moxalactam-piperacillin deserves extensive evaluation as empiric therapy for the febrile neutropenic cancer patients.