In vitro and in vivo action of mezlocillin and azlocillin combined with sisomicin.

Combined action in vitro and in vivo of ureidopenicillins (azlocillin and mezlocillin) with sisomicin has been studied with employment of strains of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. In vitro effects of these combinations were most spectacular with Pseudomonas aeruginosa; azlocillin and sisomicin were potently synergistic. Other tested microorganisms reacted also but less markedly. Evaluation of therapeutic efficacy of ureidopenicillins combined with sisomicin was performed on 90 rabbits, infected intravenously with heavy inocula. Synergistic action has been confirmed in vivo during treatment of infections evoked by Escherichia coli and Pseudomonas aeruginosa. Therapy of these infections may be successful with doses of azlocillin or mezlocillin combined with sisomicin diminished by half, as compared with treatment of these infections with above antibiotics applied singly. Further decrease of sisomicin dosage in combined therapy of P. aeruginosa infections with ureidopenicillin is possible.