Decrease of histamine induced bronchoconstriction by caffeine in mild asthma.

BACKGROUND While high doses of caffeine may affect pulmonary function and bronchial challenge tests in patients with mild asthma, the effects of lower doses (< or = 5 mg/kg) are less well documented. Specific recommendations exist for withholding theophylline, but not caffeine, before bronchoprovocation and pulmonary function testing. METHODS To assess the effect of a single oral dose of caffeine (5 mg/kg) on FEV1 and bronchial responsiveness to histamine a double blind, placebo controlled study was performed in eight patients with mild stable asthma. RESULTS While caffeine had no effect on FEV1, mean (95% confidence interval) log PC20 histamine was significantly higher 150 minutes [caffeine = 0.99 (0.2) mg/ml, placebo = 0.53 (0.29)] and 240 minutes [caffeine = 0.89 (0.24), placebo = 0.44 (0.26)] after administration of caffeine than after placebo. CONCLUSIONS Caffeine should be excluded from the diet for a period of more than four hours before bronchial provocation testing. The exact length of time for which it must be excluded requires further study.