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DTG-Metformin Dose Cap — SCE Infectious Diseases MCQ

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ModerateAntimicrobial StewardshipDTG-Metformin Dose CapSCE Infectious Diseases

A 40-year-old man with HIV develops new-onset diabetes mellitus. He is on DTG/TAF/FTC. His HbA1c is 62 mmol/mol. His GP prescribes Metformin 500 mg TDS. Knowing the DTG-Metformin interaction, what dose adjustment is needed?

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Correct answer: D — Limit Metformin to a maximum of 1000 mg daily (e.g. 500 mg BD) when co-administered with DTG — DTG inhibits renal OCT2/MATE1, increasing Metformin levels by ~80%

DTG inhibits OCT2 and MATE1 (renal organic cation transporters), reducing Metformin renal secretion and increasing plasma levels by ~80%. BHIVA and BNF recommend capping Metformin at 1000 mg daily with DTG (rather than the usual maximum of 2000–3000 mg). This also applies to BIC (which similarly inhibits OCT2). Monitor renal function closely. Alternative glucose-lowering agents (GLP-1 agonists, SGLT2 inhibitors, DPP-4 inhibitors) can be used without DTG dose concerns.

Reference: BHIVA 2025 – ART guidelines; BNF 2024 – DTG-Metformin; Liverpool Drug Interactions