Pharmacodynamic studies in normal volunteers with MDL-899, a new arteriolar vasodilator.

We conducted pharmacodynamic studies with a new vasodilator, MDL-899. Following initial dose-ranging studies we studied eight male normotensive volunteers, each of whom received, orally, 10 mg MDL-899 or placebo in double-blind random order. MDL-899 significantly lowered standing blood pressure, the maximal effect occurring 3-6 h following drug administration. There was a significant increase in heart rate in both supine and standing positions, maximal 6-8 h postdose. Supine plasma noradrenaline concentrations were greater following MDL-899, with the greatest difference present 4 h after drug administration. Plasma renin concentrations were greater following MDL-899. Six of our subjects were also given 10 mg MDL-899 together with 100 mg atenolol, in an additional study. Atenolol increased the hypotensive effect and attenuated the tachycardia following MDL-899 alone. Side effects following MDL-899 administration included headache, lightheadedness, and tachycardia. These were reduced following atenolol coadministration. The haemodynamic profile of MDL-899 suggests that this drug acts as a direct arteriolar vasodilator in man. The observed increase in heart rate is likely mediated by reflex activation of the sympathetic nervous system.