Protective effect of nifedipine upon specific bronchial responses to isocyanates

In order to evaluate the effect of nifedipine, a calcium channel blocker, upon specific bronchial responses to isocyanates, 5 subjects with occupational asthma due to TDI were examined. Each subject was exposed to an atmosphere containing 0.01 ppm of TDI in an inhalation chamber for 15 minutes; the test was repeated on a different day 45 minutes after administration of placebo or nifedipine (20 mg sublingually) in a random fashion. Our data show an effectiveness of nifedipine at the above mentioned dose in preventing the responses arising immediately or within one hour after the exposure (cases n. 1, 2, 3, 4, 5). For preventing late responses it was necessary to repeat the administration of nifedipine (10 mg sublingually) 2 hours after the exposure (cases n. 4 and n. 5). The mechanism by which nifedipine prevents bronchial responses to isocyanates has not been elucidated.