Tolerance to inhaled Duovent. A long-term study.

Fenoterol with ipratropium bromide (Duovent) is a recently used combination between an anticholinergic and a beta-adrenergic drug useful in obtaining a more effective bronchodilatation and/or reducing the single drug doses. It has been suggested that, as in the case of beta-agonists, its clinical efficacy may be limited by the development of tolerance. We studied the effects of inhaled Duovent in 15 asthmatic patients for 3 months, using a rigidly controlled protocol. Appropriate serial physiological measurements were made at regular intervals during the 90-day study. In all instances the day-one bronchodilator response was significant, prompt and sustained: at 1, 4, 8 and 12 weeks the response was statistically the same as on day 1. It is concluded that, when the important variables are properly controlled, no evidence of tolerance to long-term therapy with Duovent is demonstrable.