penicillinclass

Penicillin class, or penicillins, are a group of beta-lactam antibiotics derived from or inspired by penicillin molds. They share a beta-lactam ring and act by inhibiting bacterial cell wall synthesis through binding to penicillin-binding proteins, which prevents peptidoglycan cross-linking and leads to bacterial lysis. Most penicillins are bactericidal, and their spectrum varies by subtype from narrow to broad.

Natural penicillins, such as penicillin G and penicillin V, are active against many streptococci and some anaerobes but are inactivated by many beta-lactamase–producing organisms. Penicillinase-resistant penicillins (nafcillin, oxacillin, dicloxacillin) target penicillinase-producing staphylococci. Aminopenicillins (amoxicillin, ampicillin) broaden activity to include some Gram-negative organisms but remain susceptible to many beta-lactamases; combinations with beta-lactamase inhibitors (for example, amoxicillin-clavulanate, ampicillin-sulbactam) extend coverage. Antipseudomonal penicillins (piperacillin, ticarcillin) target Pseudomonas and other Gram-negative bacteria and are commonly used with beta-lactamase inhibitors.

Resistance to penicillins arises from beta-lactamase enzymes, altered penicillin-binding proteins (notably in MRSA), and reduced permeability in some organisms. Pharmacokinetics vary: some penicillins are orally absorbed, others require parenteral administration; many achieve adequate CNS penetration when meninges are inflamed and are excreted renally.

Adverse effects include hypersensitivity reactions ranging from rash to anaphylaxis, as well as gastrointestinal disturbances and potential superinfections. Penicillins remain essential for a range of infections, with use guided by spectrum, pharmacokinetics, and resistance considerations, reflecting a long history of clinical impact and ongoing stewardship.