Antimicrobials/Cephalosporin & carbapenem (β-lactam)

Cephalosporins & carbapenems

also: cefalexin · cefuroxime · ceftriaxone · ceftazidime · meropenem · carbapenem

Overview

Broader β-lactams — cephalosporins by generation (broadening Gram-negative cover) and the very-broad carbapenems (reserve agents). C. diff risk and the neonatal ceftriaxone caution are key.

Mechanism

β-lactams — inhibit cell-wall synthesis (PBP binding), bactericidal. Carbapenems are the broadest-spectrum β-lactams, stable to most β-lactamases.

The agents

Cefalexin1st-gen

oral

UTI/SSTI alternative; pregnancy UTI.

Cefuroxime2nd-gen

Surgical prophylaxis.

Ceftriaxone3rd-gen

IV/IM

Meningitis (≥3 mo), gonorrhoea; AVOID in neonates (kernicterus) → cefotaxime.

Ceftazidime3rd-gen anti-pseudomonal

Pseudomonas.

Meropenemcarbapenem (reserve)

ESBL/severe sepsis; seizure risk; low penicillin cross-reactivity.

Adverse effects

C. difficileserious

Cephalosporins are high-risk.

Hypersensitivity (penicillin cross-reactivity, low)common

Ceftriaxone in neonates → bilirubin displacement (kernicterus)serious

Carbapenem seizures (high dose/renal impairment)common

Cautions & contraindications

Severe penicillin anaphylaxisall

Cross-reactivity (low but real).

Ceftriaxone in jaundiced neonates / with calcium-containing IVpaediatric

Kernicterus; precipitation.

Interactions

Alcohol with some (disulfiram-like, rare)

Monitoring & kinetics

Allergy; renal function

Oral (cefalexin) / IV. Carbapenems reserve — antimicrobial stewardship.

Choosing it

Spectrum: 1st-gen (cefalexin): Gram+ & some Gram−. 3rd-gen (ceftriaxone): broad Gram−, crosses BBB (meningitis, gonorrhoea); ceftazidime adds Pseudomonas. Carbapenems (meropenem): very broad incl. ESBL + Pseudomonas + anaerobes. None cover MRSA (except ceftaroline); cephalosporins miss Listeria + atypicals.

Source: BNF — Cephalosporins / carbapenems