Small molecule
PubChem CID 5904
Penicillin G
Pfizerpen
- Mechanism of action
- Beta-lactam, inhibits cell wall synthesis
- In plain language
- The original antibiotic — discovered by accident from a stray mold in 1928 — that stops bacteria from finishing their protective outer wall, causing them to burst; it's the same basic trick every related antibiotic on this site, including amoxicillin, still uses today.
- How it works
- Penicillin G (benzylpenicillin) is the original beta-lactam antibiotic, first identified in 1928 by Alexander Fleming at St. Mary's Hospital in London after he noticed that a contaminating mold — later identified as Penicillium notatum, now reclassified Penicillium rubens — had killed the Staphylococcus colonies growing near it on a culture plate he had left out. Fleming's own attempts to purify and stabilize the substance were unsuccessful; it was Howard Florey, Ernst Chain, and Norman Heatley at Oxford University who, in the early 1940s, developed the extraction and mass-production methods that turned penicillin into a usable drug, work for which Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine. Mechanistically, penicillin G binds to and inhibits penicillin-binding proteins (PBPs) — transpeptidase enzymes that catalyze the final cross-linking step of bacterial peptidoglycan synthesis. Without an intact, cross-linked cell wall, the bacterium cannot withstand its own internal osmotic pressure and lyses, an effect most pronounced during active growth and division. This is the same core mechanism, and the same target protein family, that every later beta-lactam antibiotic on this site — including amoxicillin, a semisynthetic descendant designed for oral bioavailability — still relies on.
- Therapeutic applications
- Per FDA-approved labeling, Penicillin G Potassium for Injection (Pfizerpen) is indicated for the treatment of serious infections — including septicemia, pneumonia, endocarditis, meningitis, anthrax, diphtheria, and syphilis, among others — caused by susceptible strains of designated microorganisms, with appropriate culture and susceptibility testing performed before treatment when possible.
- Class
- Small molecule
- Therapeutic area
- Antibiotic
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