Inconsistency of Synergy Between the β -Lactamase Inhibitor CP-45,899 and β -Lactam Antibiotics Against Multiply Drug-Resistant Enterobacteriaceae and Pseudomonas Species

Synergy between CP-45,899 and ampicillin or newer beta-lactam antibiotics against multiply drug-resistant Enterobacteriaceae and Pseudomonas species was inconsistent. In contrast, synergy between CP-45,899 and ampicillin against beta-lactamase-producing strains of Haemophilus influenzae type b and Bacteroides fragilis was consistent and marked.