The effect of trifluoperazine on bronchial responsiveness in asthma.

1. The protective effects of oral trifluoperazine (TFP) (7 mg) against standardized methacholine and histamine inhalation tests (MIT and HIT) were examined 2 and 22 h post-treatment in eight stable asthmatics using a randomized double-blind protocol. 2. A preliminary study tested whether a preceding MIT influenced the result of a subsequent HIT. 3. The mean baseline forced expiratory volumes in 1 s (FEV1) were similar prior to placebo and TFP. The mean FEV1 values 2 h after ingestion of placebo or TFP were not different from the baseline values. 4. TFP did not alter bronchial responsiveness to inhaled methacholine or histamine 2 h post-ingestion, but at 22 h the PC20 methacholine was greater than placebo, while PC20 histamine did not change. This change in methacholine responsiveness was not clinically significant. 5. There was a correlation between geometric mean provocative concentration of histamine to cause 20% fall in FEV (PC20H) for HIT performed in isolation ('separate day') and for HIT performed after MIT ('same day'). 6. The effect of inhaled TFP (10 mg/ml, nebulized for 5 min) was examined single-blind and placebo-controlled in a separate group of six stable asthmatics. 7. Inhaled TFP had a bronchoconstrictor effect in all six asthmatics. The mean fall in FEV1 was 36.4% after inhaled TFP and 2.1% after saline. 8. In the asthmatics studied, ingested TFP exhibited a weak anticholinergic effect 22 h post-treatment, but a brisk spontaneously self reverting bronchoconstrictor response was invariably seen when TFP was inhaled.