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Co-amoxiclav Mechanism — MFDS Part 1 MCQ

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ModeratePharmacologyCo-amoxiclav MechanismMFDS Part 1

A bacterial isolate from an odontogenic infection is resistant to amoxicillin because it produces a clavulanate-susceptible beta-lactamase, but it remains susceptible to co-amoxiclav. Which action of clavulanic acid accounts for this finding?

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Correct answer: C — Inactivation of susceptible bacterial beta-lactamases, preventing amoxicillin hydrolysis

Explanation lettering: E = shown as A · D = shown as B · A = shown as C · C = shown as D · B = shown as E

Clavulanic acid inactivates susceptible bacterial beta-lactamases, protecting amoxicillin from enzymatic hydrolysis; therefore, A is correct. This can restore amoxicillin activity when resistance is mediated by a beta-lactamase that clavulanate inhibits. Clavulanic acid is structurally related to beta-lactams but has no clinically useful antibacterial effect when used alone, so its role is not to provide substantial additional killing through penicillin-binding proteins (B). It does not inhibit bacterial efflux pumps (C), enhance gastrointestinal absorption of amoxicillin (D), or prolong amoxicillin exposure by reducing renal clearance (E). It cannot overcome resistance caused by mechanisms such as altered penicillin-binding proteins or beta-lactamases that are not susceptible to clavulanate.

Reference: Electronic Medicines Compendium (eMC). Co-amoxiclav 500 mg/125 mg film-coated tablets, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties. Updated 2 December 2025. https://www.medicines.org.uk/emc/product/101680/smpc