Drug interactions
Methyclothiazide + Quinidine
Severity: Major
Methyclothiazide and Quinidine: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Thiazide diuretics cause hypokalemia and hypomagnesemia, which raise the risk of quinidine-induced QT prolongation and torsades de pointes. Thiazides may also alter urinary pH and quinidine handling, but electrolyte disturbance is the main concern.
What this interaction means in plain words
Methyclothiazide and Quinidine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Diuretic-induced hypokalemia and hypomagnesemia add to quinidine's QT-prolonging effect; competition for renal tubular secretion may also play a minor role.
What to do
Monitor serum potassium and magnesium and correct deficits before and during quinidine therapy. Obtain ECG monitoring for QTc changes.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Quinidine
- Adagrasib + Quinidine Contraindicated
- Arsenic trioxide + Quinidine Contraindicated
- Artemether / lumefantrine + Quinidine Contraindicated
- Chloroquine + Quinidine Contraindicated
- Dofetilide + Quinidine Contraindicated
- Dronedarone + Quinidine Contraindicated
Frequently asked questions
Can I take Methyclothiazide with Quinidine?
MediHelp rates the interaction as major. Methyclothiazide and Quinidine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Thiazide diuretics cause hypokalemia and hypomagnesemia, which raise the risk of quinidine-induced QT prolongation and torsades de pointes. Thiazides may also alter urinary pH and quinidine handling, but electrolyte disturbance is the main concern.
How serious is the interaction between Methyclothiazide and Quinidine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor serum potassium and magnesium and correct deficits before and during quinidine therapy. Obtain ECG monitoring for QTc changes.
What other medicines interact with Quinidine?
MediHelp also lists interactions of Quinidine with, for example, Adagrasib, Arsenic trioxide, Artemether / lumefantrine. The full list is on the Quinidine page.
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