Penicillin are beta-lactam antibiotics and are used to treat bacterial infection, usually gram positive bacteria.
Mechanism of action:
Bacteria constantly remodel their peptidoglycan cell walls, simultaneously building and breaking down portions of the cell wall as they grow and divide. Β-Lactam antibiotics work by inhibiting the formation of peptidoglycan cross-links in the bacterial cell wall. The β-lactam moiety (functional group) of penicillin binds to the enzyme (DD-transpeptidase) that links the peptidoglycan molecules in bacteria.
Shortly, penicillin disturbs the normal cell wall synthesis in bacteria and make them more permeable. More permeable wall allows entering more water in the bacteria and therefore they kill the bacteria.
The portion that is responsible for the antimicrobial activity is b-lactam ring. Some bacteria secrets the enzymes called beta-lactamase or penicillinase, which splits the beta-lactam ring. This structural changes allows bacteria to become resistance.
Several drugs inhibit the penicillinase, could be combined with penicillin foe effective therapy.

  • Penicillinase-resistant penicillin (antistaphylococcal drugs)
  • Oxacillin
  • cloxacillin
  • dicloxacillin
  • Broad-spectrum penicillin:
  • Amplicillin
  • Amoxicillin
  • bacampicillin
  • Extended spectrum penicillin
  • Carbenicillin
  • Pperacillin
  • Ticarcillin
  • Natural penicillins
  • Penicllins G benzathine
  • Penicillin G procaine
  • Penicillin G sodium/potassium
  • Penicillin V