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DTG Dose Reduction After Rifampicin — SCE Infectious Diseases MCQ

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ModerateTuberculosisDTG Dose Reduction After RifampicinSCE Infectious Diseases

A 35-year-old man with HIV on DTG/TAF/FTC is prescribed Rifampicin for active TB. His DTG dose is increased to 50 mg BD as per guidelines. After 2 months of TB treatment, Rifampicin is stopped (as the isolate is confirmed pan-susceptible and he enters the continuation phase with Rifampicin still included per standard 2RHZE/4RH). When should DTG be reduced back to 50 mg OD?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — 2 weeks after the LAST dose of Rifampicin — the enzyme-inducing effect of Rifampicin takes approximately 2 weeks to fully resolve after discontinuation

Rifampicin's enzyme-inducing effect (CYP3A4, UGT1A1, P-gp) persists for approximately 2 weeks after the last dose as enzyme levels gradually return to baseline. DTG should remain at the increased dose (50 mg BD) for 2 weeks after Rifampicin cessation, then be reduced to standard dose (50 mg OD). Premature dose reduction risks subtherapeutic DTG levels and viral rebound. This is a commonly tested pharmacokinetic principle.

Reference: BHIVA 2022 – TB/HIV; BNF 2024 – Rifampicin offset; Liverpool Drug Interactions