Benzylpenicillin (Penicillin G)

How it works

It inhibits bacterial cell-wall peptidoglycan synthesis by binding penicillin-binding proteins, producing a bactericidal effect against susceptible, predominantly Gram-positive and certain Gram-negative organisms.

Prescribing in practice

• Contraindicated in penicillin hypersensitivity and used with caution in those with a history of significant beta-lactam allergy, as cross-reactivity and anaphylaxis can occur.
• It is acid-labile and not effective orally, so must be given by injection or infusion.
• Most beta-lactamase-producing staphylococci are resistant, so it is not appropriate empirically for staphylococcal infection.

Monitoring

Monitor clinical response and, with high-dose or prolonged therapy or renal impairment, watch renal function, electrolytes and for neurotoxicity.

Counselling the patient

• This penicillin is given by injection in hospital or by paramedics for serious infection.
• Report any rash, swelling or breathing difficulty immediately.
• Always mention previous penicillin reactions to staff.

Evidence & guidelines

Benzylpenicillin remains a guideline-recommended agent for susceptible streptococcal and meningococcal infections and for pre-hospital treatment of suspected meningococcal disease.