Drug interactions
Spironolactone + Sulfamethoxazole
Severity: Major
Spironolactone and Sulfamethoxazole: major interaction.
Last updated
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
Sulfamethoxazole is usually given with trimethoprim, and trimethoprim blocks epithelial sodium channels in the distal nephron, causing potassium retention. Together with spironolactone this can produce clinically significant hyperkalemia, especially in older patients and those with renal impairment or heart failure. Cases of severe hyperkalemia and associated arrhythmia have been described.
What this interaction means in plain words
Spironolactone and Sulfamethoxazole 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
Additive potassium retention, as spironolactone blocks aldosterone receptors and trimethoprim (in co-trimoxazole) inhibits distal sodium channels.
What to do
Avoid co-trimoxazole in patients on spironolactone where alternatives exist. If it cannot be avoided, check serum potassium and creatinine within a few days and again during therapy.
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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Other interactions of Spironolactone
- Amiloride + Spironolactone Contraindicated
- Eplerenone + Spironolactone Contraindicated
- Spironolactone + Triamterene Contraindicated
- Abiraterone + Spironolactone Major
- Aceclofenac + Spironolactone Major
- Acemetacin + Spironolactone Major
Frequently asked questions
Can I take Spironolactone with Sulfamethoxazole?
MediHelp rates the interaction as major. Spironolactone and Sulfamethoxazole 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. Sulfamethoxazole is usually given with trimethoprim, and trimethoprim blocks epithelial sodium channels in the distal nephron, causing potassium retention. Together with spironolactone this can produce clinically significant hyperkalemia, especially in older patients and those with renal impairment or heart failure. Cases of severe hyperkalemia and associated arrhythmia have been described.
How serious is the interaction between Spironolactone and Sulfamethoxazole?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid co-trimoxazole in patients on spironolactone where alternatives exist. If it cannot be avoided, check serum potassium and creatinine within a few days and again during therapy.
What other medicines interact with Spironolactone?
MediHelp also lists interactions of Spironolactone with, for example, Amiloride, Eplerenone, Triamterene. The full list is on the Spironolactone page.
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