bètalactam

Bètalactams are a class of antibiotics defined by a four-membered β-lactam ring in their core structure. Members include penicillins, cephalosporins, monobactams and carbapenems, with side chains that modify spectrum, stability to enzymes, and pharmacokinetic properties.

Mechanism of action: They inhibit bacterial cell wall synthesis by binding penicillin-binding proteins, blocking peptidoglycan cross-linking. Most are bactericidal and require bacterial growth for maximal effect.

Spectrum and subclasses: Penicillins and some cephalosporins target many Gram-positive bacteria; later generations broaden Gram-negative activity. Carbapenems are among the broadest-spectrum β-lactams; monobactams (such as aztreonam) primarily cover Gram-negative organisms and are generally not active against Gram-positive bacteria.

Resistance: Major mechanisms include beta-lactamase enzymes that hydrolyze the β-lactam ring, altered penicillin-binding proteins, reduced outer-membrane permeability, and efflux pumps. Clinically important enzymes include ESBLs, AmpC, and carbapenemases. Some pathogens gain resistance through altered PBPs (e.g., MRSA).

Clinical use and safety: Beta-lactams are widely used for a broad range of infections. Common adverse effects are hypersensitivity reactions, rash, and gastrointestinal upset. Cross-reactivity between penicillins and some cephalosporins exists, especially with older structures; severe allergies require caution. Inhibitors of beta-lactamases (e.g., clavulanic acid) extend activity of several agents.

History: The discovery of penicillin by Alexander Fleming in 1928 led to the development of the beta-lactam class, followed by semi-synthetic penicillins, cephalosporins, and later carbapenems and monobactams.