INHALED ATROPINE SULFATE - DOSE-RESPONSE CHARACTERISTICS

Abstract

The dose-response characteristics of atropine sulfate were examined in 20 children with chronic perennial asthma, using maximal expiratory flow-volume curves. Inhaled drug was delivered in incremental doses of 0.005-0.1 mg/kg. A peak action of atropine on the maximal flow after exhalation of 50% of the forced vital capacity was seen 1 h 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, 0.05-0.1 mg/kg. Changes in the maximal expiratory flow after exhalation of 75% of the forced vital capacity paralleled those in the maximal expiratory flow after exhalation of 50% 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. Atropine sulfate by inhalation is an effective bronchodilator in children with severe asthma and reported variations in its efficacy may be related to inadequate dosage.