II. ACE inhibitors and Allopurinol
Cases of Stevens-Johnson syndrome and hypersensitivity have been attributed to the use of captopril with allopurinol. The risk of leucopenia and serious infection may increase when these two agents are used in combination. 
- An elderly man was suffering from CHF, chronic renal failure, hypertension and multiple polyarthritis. As part of a multiple drug therapy, he was given captopril 25 mg twice daily and diuretics. He developed a fatal condition of Stevens-Johnson syndrome after 5 weeks of starting Allopurinol, 100 mg twice daily. 
- Another patient with renal failure suffered with exfoliatory facial dermatitis on taking captopril and allopurinol. 
- Another man on enalapril experienced an acute anaphylactic reaction with severe coronary spasm and myocardial infarction within 20 minutes of taking allopurinol. 
- The maker of captopril warns that neutropenia or agranulocytosis resulting in serious infections have been observed in patients taking captopril and other ACE inhibitors. Concurrent use of allopurinol may be an additional complicating factor, especially in patients with renal impairment. 
There is no established mechanism.
* The reactions appear to be rare and unpredictable and there exists no established mechanism for the interactions.
* The patients on combination therapy of these two drugs must be closely monitored for signs of hypersensitivity or low white cell count, especially if they have renal impairment. The maker of captopril recommends a differential count before combination therapy is started and must be followed every 2 weeks after commencement of therapy. 
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