Penicillins
also: amoxicillin · benzylpenicillin · flucloxacillin · co-amoxiclav · Tazocin · penicillin
Overview
The β-lactam workhorses — bactericidal cell-wall agents spanning narrow (benzylpenicillin) to very broad (piperacillin-tazobactam). Penicillin allergy and the EBV-amoxicillin rash are core.
Mechanism
Bind penicillin-binding proteins → inhibit peptidoglycan cross-linking → bacterial cell-wall lysis (bactericidal). β-lactamase inhibitors (clavulanate/tazobactam) protect against breakdown.
The agents
IV / oral
Strep throat (penV), pre-hospital meningococcal (IV benzylpen).
PO/IV
CAP, otitis media; rash with EBV (not true allergy).
PO/IV
Cellulitis, MSSA; cholestatic jaundice (delayed).
PO/IV
Bites, aspiration, intra-abdominal; C. diff risk + cholestasis.
IV
Neutropenic sepsis, HAP.
Adverse effects
True allergy (~1–10% cross-reactivity with cephalosporins/carbapenems is low).
NOT a true penicillin allergy.
Cautions & contraindications
Anaphylaxis; severe penicillin anaphylaxis → avoid cephalosporins/carbapenems too.
Interactions
- Probenecid raises levels; broad-spectrum agents ↓OCP efficacy via gut flora (counsel)
Monitoring & kinetics
Allergy status; renal function for high IV doses
Oral / IV. Time-dependent killing.
Choosing it
Spectrum: Benzyl/phenoxymethyl: Gram-positive (Strep, meningococcus, Treponema). Amoxicillin: + some Gram-negatives, Enterococcus, Listeria. Flucloxacillin: anti-staphylococcal (MSSA — NOT MRSA). Co-amoxiclav: + β-lactamase producers/anaerobes. Pip-tazobactam: very broad incl. Pseudomonas. None cover atypicals or MRSA.
Source: BNF — Penicillins · NICE CKS — Antibacterials