Quinacillin is semisynthetic penicillase-resistant penicillin patented by Boots Pure Drug Co. Ltd. For the treatment of bacterial infection. Quinacillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and results in the weakening of the bacterial cell wall, eventually causing cell lysis. In clinical trials Staph. aureus was eradicated from all but two patients during treatment but recurred in 4 after withdrawal. The antibiotic was especially useful in the treatment of staphylococcal respiratory infections, as it has little effect on the normal bacterial flora of the chest.