methicillin

Methicillin is a semisynthetic narrow-spectrum β-lactam antibiotic of the penicillin class. It was developed in the late 1950s to treat infections caused by Gram-positive bacteria—particularly penicillinase-producing organisms such as Staphylococcus aureus that are resistant to other penicillins. Methicillin is bactericidal and acts by inhibiting bacterial cell wall synthesis through binding to and inactivating penicillin-binding proteins (PBPs), which are essential for peptidoglycan cross-linking in bacterial cell walls. The drug’s bulky side chain confers resistance to hydrolysis by most staphylococcal β-lactamases (penicillinases). However, it is not effective against bacteria that have acquired the mecA gene encoding PBP2a with low affinity for β-lactams—a mechanism underlying methicillin-resistant Staphylococcus aureus (MRSA). Methicillin was administered parenterally due to its instability in gastric acid and has been discontinued from clinical use because of widespread resistance and adverse effects such as interstitial nephritis. Its role has largely been replaced by other penicillins like oxacillin and flucloxacillin[1][3][4][5][7].

Brand names

Staphcillin

Other names

(2,6-Dimethoxyphenyl)penicillin6-(2,6-dimethoxybenzamido)penicillanic acid