Major
Allopurinol × Captopril
Xanthine oxidase inhibitors×ACE inhibitor
Mechanism
The combination raises risk of hypersensitivity reactions and severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema). The mechanism is not fully established; presumed to be an immune reaction to metabolites of both drugs in chronic kidney disease.
Symptoms
Rash, fever, eosinophilia, lymphadenopathy (DRESS syndrome). Severe cases: bullous rash with skin sloughing (Stevens-Johnson syndrome), angioedema of face and tongue. Symptoms appear 1–8 weeks into the combination.
Management
Avoid the combination, especially in chronic kidney disease (higher risk). Alternative to ACE-I: an ARB (losartan) for antihypertensive needs. If rash or fever emerges, stop both drugs immediately.
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.