Combination of ceftizoxime with azlocillin, mezlocillin, piperacillin and ticarcillin

Combination of two β -lactam agents has been used to enlarge the antibacterial spectrum of both the penicillin and cephalosporin components of the combination. However, some β-lactamase-stable cephalosporins by virtue of their induction of β-lactamases, cause destruction of the penicillins. Combination of ceftizoxime with azlocillin, meziocillin, piperacillin and ticarcillin showed synergy for 6.5–12%, an additive action for 9.8–25% and antagonism for only 1–3% of the 92 Enterobacteriaceae and Pseudomonas isolates tested. In contrast, combination of cefoxitin with the penicillins showed antagonism against 4–18% of isolates. Combination of ceftizoxime and oral antipseudomonas penicillins did not render strains resistant to the antipseudomonas penicillins susceptible. In no instance did the combination of ceftizoxime with an antipseudomonas penicillin cause an increase in minimal inhibitory concentration that would make the antagonism clinically significant.