Comparative effects of oral and inhaled verapamil on antigen-induced bronchoconstriction

We investigated the comparative effects of oral and inhaled verapamil on specific airway conductance (SGaw) and allergic bronchial reactivity. Ten asymptomatic subjects with ragweed hypersensitivity and a history of bronchial asthma were studied on four different days, without and with pre-treatments by oral (160 mg) or inhaled (20 mg) verapamil. Bronchial reactivity was measured as the cumulative provocative dose of ragweed antigen which caused a 35 percent decrease in SGaw, ie PD35. The amount of inhaled verapamil actually deposited in the tracheobronchial tree was estimated to be 0.56 mg. Mean SGaw was not affected by either mode of administration; mean SGaw (SE) was 0.13(.02) and 0.12(.02) L/sec-1 before and .14(.02) and 0.12(.02) L/sec-1 after oral and inhaled verapamil, respectively. Mean (SE) PD35 was reproducible on two control days, ie 0.9(.4) and 0.8(.4) breath units, respectively. Inhaled verapamil increased mean PD35 to 18.8 (10.8) breath units (p less than 0.02), while oral verapamil had no significant effect on mean PD35. This study demonstrates that route of administration of calcium antagonist verapamil is an important factor in protection against antigen-induced bronchoconstriction. Inhalation of verapamil appears to be more effective than oral administration.