nafcillin

Nafcillin is a beta-lactam antibiotic in the penicillin class, specifically a penicillinase-resistant penicillin. It was developed to resist degradation by penicillinase enzymes produced by certain Staphylococcus aureus strains, enabling it to treat penicillinase-positive staphylococcal infections. Its antibacterial effect is bactericidal and results from inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins.

Nafcillin has activity primarily against penicillinase-producing Staphylococcus aureus and some streptococci. It has limited activity against most Gram-negative bacteria and Enterococcus species and is not effective against methicillin-resistant Staphylococcus aureus (MRSA). Clinically, it is used for serious staphylococcal infections such as skin and soft tissue infections, osteomyelitis, septic arthritis, endocarditis, and pneumonia caused by penicillinase-producing S. aureus. It is not appropriate for MRSA infections.

Administration is parenteral only; nafcillin is given intravenously or intramuscularly and is not effective when taken orally due to poor absorption. Typical adult dosing is around 2 g IV every 4 hours, with adjustments based on severity and clinical response. Nafcillin is predominantly eliminated by hepatic metabolism with biliary excretion, and routine renal dose adjustments are not typically required, though hepatic impairment may necessitate modification.

Adverse effects include hypersensitivity reactions, rash, and fever. A characteristic adverse effect is cholestatic liver injury with elevations in liver enzymes and jaundice; neutropenia and eosinophilia can also occur. Phlebitis can accompany IV administration. Cautions include potential cross-reactivity in penicillin-allergic individuals and possible interactions with anticoagulants such as warfarin.