True penicillin anaphylaxis: avoid all beta-lactams including cephalosporins and carbapenems, and use a non-beta-lactam alternative per indication. A simple non-severe rash is not an absolute contraindication (seek advice).
Before prescribing
- Indication, likely organism, severity, and the need for source control
- Take a detailed allergy history (distinguish a rash from anaphylaxis)
- Renal and hepatic function, pregnancy and breastfeeding, interactions
- Send cultures before the first dose where feasible, but do not delay in sepsis
Pregnancy and cautions
- Avoid trimethoprim in the first trimester (folate antagonist), nitrofurantoin at term
- Avoid tetracyclines and fluoroquinolones in pregnancy and children
- Fluoroquinolones: tendon, aortic and neuropsychiatric warnings; macrolides and some others prolong the QT
- Check for C. difficile risk with broad-spectrum agents
Uncomplicated infection
- Narrow-spectrum, oral, shortest course
- Follow the local guideline
- Check allergy status
Moderate / specific
- Broaden only if indicated
- Adjust for renal function
- Review at 48 to 72 h
Sepsis
- IV broad-spectrum within 1 h
- Cultures first if no delay
- De-escalate on results
Prescribing loop
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1. Follow the guideline
Use the local antimicrobial formulary first, chosen by indication and severity.
Use the local antimicrobial formulary first, chosen by indication and severity.
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2. Dose correctly
Right dose, route and frequency; adjust for renal or hepatic function and weight; give IV in severe infection or sepsis.
Right dose, route and frequency; adjust for renal or hepatic function and weight; give IV in severe infection or sepsis.
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3. Review at 48 to 72 h
Review against cultures: stop if not infection, de-escalate to a narrow agent, switch IV to oral when stable, and set a stop or review date.
Review against cultures: stop if not infection, de-escalate to a narrow agent, switch IV to oral when stable, and set a stop or review date.
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4. Document
Record the indication, route and intended duration on the chart to support review and stewardship.
Record the indication, route and intended duration on the chart to support review and stewardship.
Stewardship principles
- Narrowest effective spectrum for the shortest effective course
- IV-to-oral switch as soon as the patient allows
- Review every antibiotic at 48 to 72 h
- Protect against C. difficile and resistance
Pitfalls
- Giving a cephalosporin or carbapenem in penicillin anaphylaxis
- Trimethoprim in early pregnancy, tetracyclines in pregnancy or children
- No documented indication or review date
- Delaying antibiotics in sepsis to await cultures
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026