Methicillin

Methicillin is a semisynthetic penicillin antibiotic designed to resist staphylococcal penicillinase. It was used against penicillinase-producing staphylococci but has largely been replaced by other drugs.

Penicillin-binding proteins: Bacterial enzymes that build and remodel peptidoglycan in the cell wall. Methicillin kills susceptible bacteria by binding these enzymes and disrupting cell-wall construction.
Alexander Fleming: Scottish bacteriologist who discovered penicillin's antibacterial action in 1928. The discovery began the antibiotic era that methicillin later addressed.
Methicillin-resistant Staphylococcus aureus: Staphylococcus aureus strains resistant to methicillin and related beta-lactam antibiotics. MRSA takes its name from resistance to this drug, though testing now relies on related agents.
Vancomycin: A glycopeptide antibiotic that inhibits bacterial cell-wall synthesis through a target distinct from beta-lactams. It became a major treatment option for serious MRSA infections when methicillin cannot work.
Beta-lactam antibiotics: Antibiotics whose beta-lactam ring disrupts bacterial cell-wall synthesis. Methicillin belongs to this broad drug family.
Penicillin: A group of beta-lactam antibiotics first derived from Penicillium fungi. Methicillin was developed as a penicillin resistant to staphylococcal penicillinase.
Oxacillin: A penicillinase-resistant penicillin used in treatment and laboratory testing for staphylococcal susceptibility. It replaced methicillin in many susceptibility tests because it is more stable and practical.
Nafcillin: A penicillinase-resistant penicillin used for susceptible staphylococcal infections, especially in the United States. It shares methicillin's antistaphylococcal purpose but remains a treatment drug.
Penicillinase: A bacterial beta-lactamase enzyme that inactivates penicillin by opening its beta-lactam ring. Methicillin's bulky side chain was designed to hinder this enzyme.
Staphylococcus aureus: A bacterial species that can cause infections ranging from skin disease to bloodstream infection. Penicillinase-producing strains prompted the development of methicillin.

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CloxacillinCompared with: Cloxacillin is a later related drug; methicillin now chiefly appears in resistance terminology and laboratory testing.