Comparison of a new beta adrenergic blocker (MK 950) and propranolol in man

The effects of oral doses of MK 950 and propranolol on heart rate in the sitting and standing positions were measured in 6 volunteers. Although the response to beta blockade is related to the initial heart rate and to the log of the dose of the drug, multiple regression analysis made it possible to separate these interactions. In a dose of 2.5 mg. orally, MK 950 reduced heart rate to the same degree as did 20 mg. of propranolol. The regression lines relating dose to response of the heart rate was steeper for MK 950 than for propranolol. There was a fall of about 20 per cent in heart rate and cardiac output after 5 mg. of MK 950, with little change in stroke volume or blood pressure. MK 950 blocked the response to isoproterenol infusion in doses up to 8 µg per minute and reduced the heart rate response to tilting and amylnitrite inhalation and the pressure overshoot in Valsalva maneuver.