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Penicillin Allergy Antibiotics — MFDS Part 1 MCQ

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ModeratePharmacologyPenicillin Allergy AntibioticsMFDS Part 1

A 35-year-old immunocompetent adult has an acute apical abscess associated with facial swelling and fever. The abscess is drained, there is no airway compromise, and adjunctive oral antibiotic treatment is indicated. The patient has a confirmed history of immediate anaphylaxis following penicillin. Which is the most appropriate antibiotic regimen?

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Correct answer: D — Metronidazole 400 mg three times daily for 5 days

The correct answer is D. Facial swelling and fever establish spreading and systemic infection, so an antibiotic is indicated as an adjunct to drainage. In a patient with immediate penicillin anaphylaxis, metronidazole 400 mg three times daily for up to 5 days is an appropriate UK dental regimen. Co-amoxiclav, amoxicillin and phenoxymethylpenicillin all contain penicillin and must not be prescribed after confirmed penicillin anaphylaxis. Cefalexin is a cephalosporin rather than a penicillin, but cross-allergenicity and severe reactions, including anaphylaxis, are recognised; it is not the preferred dental alternative here. Antibiotics alone do not eliminate the source of an odontogenic infection, so drainage and definitive treatment by root canal therapy or extraction remain essential.

Reference: NHS Forth Valley, Antimicrobial Prescribing: Dental abscess, penicillin-allergy regimen, current online guidance, checked August 2026. https://www.rightdecisions.scot.nhs.uk/antimicrobial-prescribing-nhs-forth-valley/acute-hospital-guidance/oral-maxillofacial/dental-abscess/