Iron dark stools — GPhC CRA MCQ

Correct answer: C — Separate iron and doxycycline using the product-specific administration interval

Separate iron and doxycycline using the product-specific administration interval: Oral iron forms poorly absorbed complexes with tetracyclines; a clear timing plan is needed rather than simultaneous administration. Take iron and doxycycline together with a full glass of milk: Milk adds another chelating cation and does not prevent the interaction. Crush iron and doxycycline together immediately before each scheduled dose: Crushing does not prevent chemical complex formation and may be unsuitable for the formulations. Increase the doxycycline dose on days when iron treatment continues: Unauthorised dose escalation is not a safe substitute for separating administration. Separate doxycycline and iron by thirty minutes at each morning dose: Thirty minutes is shorter than the product-specific administration interval and does not reliably prevent iron–doxycycline chelation.

Reference: BNF: ferrous sulfate: https://bnf.nice.org.uk/drugs/ferrous-sulfate/