MajorSulfonamide-trimethoprim combination×Angiotensin-converting enzyme inhibitors (ACEi)
Updated · Methodology
Mechanism
Trimethoprim blocks collecting duct sodium channels (amiloride-like mechanism) and reduces potassium secretion. Enalapril (ACE-I) additionally retains potassium through aldosterone suppression.
Symptoms
Muscle weakness, paraesthesia in the limbs, slowed pulse, arrhythmias. ECG shows peaked T waves and widened QRS. Severe cases progress to cardiac arrest. Symptoms typically appear within 1–2 weeks of starting the combination.
Management
During co-trimoxazole therapy, check potassium 3–5 days after start. In older patients and chronic kidney disease, prefer alternative antibiotics: nitrofurantoin or fosfomycin.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- PubMed: Trimethoprim-sulfamethoxazole and risk of sudden death among patients taking spironolactone or ACE inhibitors (2014)
- AEMPS: Ficha técnica: Enalapril (nº registro 63355), sección 4.5 (2025)– AEMPS, CIMA, nº registro 63355, revisión 08/2025, sección 4.5