Apalcillin (PC-904) combined with Ro 48-1220 (a penicillin sulfone β-lactamase inhibitor) exhibits broad-spectrum activity against Gram-negative aerobic and anaerobic bacteria, excluding Klebsiella acid-producing strains. This combination shows strong efficacy against β-lactamase-producing Moraxella catarrhalis, Haemophilus influenzae, and Neisseria gonorrhoeae with an effective MIC of 11 μg/mL. Additionally, it inhibits Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Acinetobacter at low MICs (0.25 to 4 μg/mL). However, it has limited efficacy against oxacillin-resistant staphylococci and some Gram-positive bacteria. Apalcillin/Ro 48-1220's effectiveness against certain extended-spectrum β-lactamase-producing Escherichia coli is comparable to piperacillin/tazobactam, though it is less effective against SHV-type β-lactamases.