Effects of labetalol and propranolol on histamine-induced bronchoconstriction in normal subjects.

1 The effects of oral propranolol (80 mg), labetalol (400 mg) and placebo on blood pressure, pulse rate and FEV1 at rest and after inhaled histamine, have been compared in six healthy male volunteers. 2 At 90 and 120 min after ingestion propranolol reduced the pulse rate and labetalol reduced the blood pressure, thus confirming absorption of each drug. 3 At 120 min propranolol reduced resting FEV1 and enhanced the fall in FEV1 after histamine, whereas the alterations in FEV1 after labetalol did not differ from placebo. 4 These findings suggest that labetalol is less likely than propranolol to cause bronchoconstriction in asthmatic patients.