Thirty one children with asthma were given 40 micrograms of ipratropium bromide and identical placebo by inhalation three times a day in a double blind, randomised crossover study to test the ability of an anticholinergic drug to modify the diurnal variation in airway calibre and bronchial reactivity. Subjects measured peak expiratory flow rate approximately eight hourly, before and after inhaled salbutamol, for four week periods. Paired t tests and cosinor analysis were used to assess the diurnal variation in airway calibre from the peak expiratory flow rate recorded before salbutamol and to assess the diurnal variation in bronchodilator responsiveness from the increase in peak expiratory flow rate after salbutamol. Maintenance treatment with ipratropium bromide 40 micrograms three times daily reduced the provocative dose of histamine which caused a 20% fall in FEV1 (geometric mean PD20 = 0.78 v 0.49 mg/ml, p less than 0.05), despite an eight to 12 hour gap between the last dose of ipratropium and histamine challenge. It did not, however, diminish the diurnal variation in airway calibre (mean amplitude = 12.7 v 10.1) or in bronchodilator responsiveness (mean amplitude = 62.4 v 63.5). There was no improvement in the clinical state of subjects while they were taking ipratropium bromide.
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