Inhaled atropine sulfate: dose response characteristics.

Inhaled atropine sulfate is a bronchodilator in man, but its efficacy and optimal dosage are still unknown. In the current study, the dose-response characteristics of this agent were examined in 20 children with chronic perennial asthma, using maximal expiratory flow-volume curves. Inhaled drug was delivered in incremental doses of 0.005 to 0.1 mg per kg. A peak action of atropine on the maximal flow after exhalation of 50 per cent of the forced vital capacity was seen 1 hour after inhalation; significant bronchodilatation was observed for as long as 300 min, depending on the dose. A plateau was observed in the dose-response curve in the dose range, 0.05 to 0.1 mg per kg. Changes in the maximal expiratory flow after exhalation of 75 per cent of the forced vital capacity paralleled those in the maximal expiratory flow after exhalation of 50 per cent of the forced vital capacity. Specific conductance significantly increased, and the ratio of residual volume to total lung capacity significantly decreased in 10 patients examined. In no case could the observed increases in flows be explained by the patient's breathing at a higher lung volume. Considerable intersubject variation was found in the effects of a given dose of atropine. This may be explained by variations in baseline flows. It was concluded that atropine sulfate by inhalation is an effective bronchodilator in children with severe asthma and that reported variations in its efficacy may be related to inadequate dosage.