The dose-response relationships of ipratropium bromide were assessed by two different techniques in two groups of 10 male patients with partially reversible airways obstruction. In a randomised double-blind fashion on four days, 10 patients were given 40 μg, 80 μg, or 120 μg of ipratropium bromide or placebo from identical containers. Baseline FEV1 and vital capacity were measured and the measurements repeated after 40 minutes, one, two, four, and six hours, and any symptoms were elicited. In the second study, each patient received cumulative doses of 40 μg, 80 μg, and 120 μg. Baseline FEV1 was obtained and repeated 35 minutes after each dose. The peak increase of the FEV1 was comparable in both studies. The FEV1 was slightly greater after 120 μg than after 40 μg. Although this reached statistical significance only in the first study, it was concluded that the cumulative dose-response technique was suitable for determining the peak response. However, this technique was unsuitable for assessing duration of effect, which could be examined only in the first study. After 120 μg of ipratropium bromide, the FEV1 was significantly greater than after 40 μg at each time interval and it was greater than 80 μg at six hours (p<0·05). No significant side effects were noted in either study. When prolonged effective bronchodilation is sought, a dose of 120 μg of ipratropium bromide may be preferable to the recommended dose of 40 μg.
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