ObjectiveTo assess the pharmacodynamics and pharmacokinetics of single oral doses of a new vasodilator‐cardiotonic agent, 349U85 hydrochloride [6‐piperidino‐2(lH)‐quinolinone hydrochloride], in healthy male subjects.MethodsThis randomized, parallel, double‐blind, placebo‐controlled, dose escalation trial was conducted at a university‐based clinical research center among 27 healthy male subjects. Data measurements used in the study included cardiac index, supine and standing blood pressure, 24‐hour ambulatory electrocardiography, and 12‐lead electrocardiography.ResultsDoses from 2 mg to 250 mg were well tolerated. Cardiac index, supine heart rate, and orthostatic hypotension, indicators of inotropic, chronotropic, and vasodilator effects, respectively, correlated to plasma concentrations of 349U85 and of its metabolite, 661U88. Results suggest that 349U85 may be more responsible for inotropic effects, whereas 661U88 may be more responsible for vasodilatory and chronotropic effects. These results are consistent with the preclinical pharmacologic profile for these two compounds. Headache, orthostatic dizziness, and hypotension tended to occur more frequently at higher doses and were temporally related to drug administration. Pharmacokinetic analyses indicate nonlinearity of 349U85 and 661U88, suggestive of saturation of metabolism and large interindividual variability in maximum plasma drug concentration and area under the plasma concentration—time curve. The source of the variability is not known. The time to maximum distribution was approximately 0.7 hours for both 349U85 and 661U88; the terminal elimination half‐life was 1 hour for 349U85 and 3 hours for 661U88. Holter monitoring revealed asymptomatic increases in ventricular and supraventricular ectopic activity in some volunteers; ectopy appeared to be related to the dose of 349U85 and generally occurred at higher doses.Clinical Pharmacology and Therapeutics(1994)55,55–63;