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Clarithromycin statin — GPhC CRA MCQ

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HardInfection ManagementClarithromycin statinGPhC CRA

A prescription requires magnesium sulfate 4 g intravenously before dilution. Stock is magnesium sulfate 50% w/v solution for injection. What volume of stock solution contains the prescribed dose?

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Correct answer: A — 8 mL

A 50% w/v solution contains 50 g in 100 mL, equivalent to 500 mg/mL. A 4 g dose is 4,000 mg, and 4,000 ÷ 500 = 8 mL, making Option A correct. Option C assumes 2 g/mL. Option E treats 50% as 1 g/mL. Option D uses an incorrect 667 mg/mL. Option B interprets the stock as 40% w/v. The calculated stock volume still requires appropriate IV dilution.

Reference: Magnesium sulfate 50% SmPC: https://www.medicines.org.uk/emc/product/3539/smpc; GPhC framework: https://assets.pharmacyregulation.org/files/2025-09/Common-Registration-Assessment-framework-for-sittings-in-2026.pdf