antibiotic drug of the penicillin family used in the treatment of certain staphylococcal infections

Methicillin (USAN) or meticillin (INN, BAN) is a narrow spectrum beta-lactam antibiotic. It was previously used to treat infections caused by susceptible Gram-positive bacteria, particularly beta-lactamase-producing organisms such as Staphylococcus aureus that would otherwise be resistant to most penicillins, but is no longer clinically used. Its role in therapy has been largely replaced by flucloxacillin and dicloxacillin, however the term methicillin-resistant Staphylococcus aureus (MRSA) continues to be used to describe Staphylococcus aureus strains resistant to all penicillins.