Apalcillin is a naphthydridine derivative of ampicillin. Apalcillin has a broad spectrum of antibacterial activity that is very similar to that of piperacillin, except that apalcillin is significantly more active against Pseudomonas aeruginosa and Acinetobacter spp. Against Acinetobacter spp., apalcillin is uniquely active, compared to the other penicillins and comparison drugs. Strains producing high amounts of β-lactamases do become resistant to apalcillin. PAH (p-aminohippurate) clearance was significantly decreased during apalcillin infusion. Apalcillin appeared to compete with PAH for proximal tubular secretion but induced no further renal dysfunction.