LACK OF SHORT-TERM EFFECT OF THE THROMBOXANE SYNTHETASE INHIBITOR UK-38,485 ON AIRWAY REACTIVITY TO METHACHOLINE IN ASTHMATIC SUBJECTS

Previous open studies have suggested that thromboxane receptor antagon ists or synthesis inhibitors lower airway hyperresponsiveness in human subjects. This would indicate a role of thromboxane A2 in the develop ment or maintenance of hyperresponsiveness in asthma. Ten nonsmoking a sthmatics (aged 23-64 yrs, 9 male) were included in a randomized, doub le-blind, placebo-controlled, cross-over study of the effect of one we ek of treatment with a potent selective thromboxane synthetase inhibit or (UK-38,485, 600 mg daily) on airway responsiveness. The study was p receded by a two week run-in period, and two weeks were used for wash- out between the two trial periods. Adequacy of dosage and patient comp liance was confirmed by a reduction in the ex vivo formation of thromb oxane B2 (median concentration 3.22 mug.ml-1 after placebo, 0.10 mug-m l-1 after UK-38,485, p<0.05). The mean forced expiratory volume in one second (FEV1) after UK-38,485 was 2.55 l, compared to 2.56 1 after tr eatment with placebo (p=0.74). The geometric mean provocative dose of methacholine producing a 20% fall in FEV1 (PD20) before and after UK-3 8,485 was 23.9 and 32.2 mug, respectively, compared to 25.1 and 26.3 m ug respectively, before and after placebo (p=0.31). The results of thi s study suggest that thromboxane A2 does not play an important role in the maintenance of increased airway responsiveness in moderately seve re asthmatics treated with low doses of inhaled steroids.