Ampicillin

How it works

It inhibits bacterial cell wall synthesis by binding penicillin-binding proteins, leading to bacterial lysis.

Prescribing in practice

• It is contraindicated in patients with penicillin hypersensitivity, who are at risk of anaphylaxis.
• A maculopapular rash is common if given in glandular fever (infectious mononucleosis) and it should be avoided in this setting.
• Many common organisms produce beta-lactamases conferring resistance, so therapy should be guided by susceptibility where possible.

Monitoring

Monitor for hypersensitivity reactions and clinical response, and review renal and hepatic function with prolonged or high-exposure treatment.

Counselling the patient

• Report any rash, swelling or breathing difficulty, which may indicate allergy.
• Complete the full prescribed course even if you feel better.
• Tell your prescriber if you have ever reacted to a penicillin.

Evidence & guidelines

Ampicillin and related aminopenicillins are long-established agents with well-defined roles in UK antimicrobial guidance.