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Nitrate tolerance — GPhC CRA MCQ

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HardCardiovascular TherapeuticsNitrate toleranceGPhC CRA

A 63-year-old man with stable angina is prescribed isosorbide mononitrate 20 mg modified-release once daily. He takes it at 8am. He experiences angina episodes most evenings. What is the most likely explanation for the evening symptoms?

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

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Correct answer: C — Nitrate tolerance has developed due to continuous nitrate exposure

Continuous nitrate exposure leads to tolerance, reducing therapeutic efficacy. Standard practice is to ensure a nitrate-free interval of at least 8-12 hours, typically overnight. A once-daily modified-release preparation taken in the morning provides cover during the day with a drug-free period overnight. However, if symptoms occur in the evening, the timing or regimen may need adjustment. The GP should review to ensure the nitrate-free period aligns with the patient's symptom pattern.

Reference: BNF Nitrates; NICE CKS Angina