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Angiotensin-converting-enzyme (ACE) inhibitors approved in Canada are indicated for the treatment of mild to moderate essential hypertension. Some ACE inhibitors are also indicated for congestive heart failure or diabetic nephropathy or for use after myocardial infarction. Those available in Canada are benazepril hydrochloride, captopril, cilazapril, enalapril maleate, enalaprilat, fosinopril sodium, lisinopril, perindopril erbumine, quinapril hydrochloride and ramipril. A dry, tickly, persistent and often bothersome cough is one of the most common adverse effects of ACE inhibitors that has emerged as a class effect and seems to be independent of the dose. This symptom may occur shortly after therapy is started but also months or even a year later. The cough will usually resolve within a few days after withdrawal of the ACE inhibitor.(f.1) The relationship between ACE inhibitors and bronchial hyperresponsiveness, however, has not been as clearly established.(f.2) It has been proposed that ACE inhibitor-induced bronchospasm may be caused by potent bronchoconstrictors such as bradykinin and substance P, which are degraded by ACE and may accumulate in the lungs of patients receiving ACE inhibitors.(f.2) It has also been postulated that an ACE inhibitor-induced cough may be due to an irritant inflammatory state in the airways of susceptible patients and that this symptom may have pathophysiological features in common with the cough seen as an early symptom of asthma.(f.3) However, other mechanisms of ACE inhibitor-induced cough and bronchospasm have been proposed, and the exact mechanism involved still remains unknown.(f.1,4) Although ACE inhibitors are safe for use in most patients with obstructive airway disease, there have been occasional reports of asthmatic symptoms, exacerbation of asthma or a rise in bronchial reactivity; however, these findings have not been universal.(f.1,2) Two large retrospective studies have evaluated reported adverse respiratory reactions associated with ACE inhibitors. One, a controlled cohort study in New Zealand, found a significantly higher occurrence of new-onset bronchospasm and a relapse of previous bronchospasm in the cohort treated with an ACE inhibitor than...