Hemodynamic and humoral effects at rest and after head-up tilt tests during 24-hour infusion of a new nitrate ester, ITF 296, compared with ISDN and placebo in healthy volunteers: a double-blind, randomized, within-subject study.

A double-blind, randomized, three-way complete crossover study was carried out to compare pharmacodynamic effects and tolerability during a 24-h intravenous infusion of ITF 296, isosorbide dinitrate (ISDN), and placebo, in the supine position and during 70 degrees head-up tilt. Ten healthy men aged 21-34 years participated in the study to obtain complete data in nine. Dosing started at 1 microgram/kg/min and was titrated up during the first 30 min of infusion, to produce a 10% reduction in diastolic blood pressure (DBP). At least 6 days elapsed between consecutive treatments. Heart rate (HR) and blood pressure were measured at least half hourly throughout the infusion period and up to 2 h afterwards. Systolic time intervals were measured before and at 0.5, 1, 2, 3, and 24 h of infusion in the fasting state. Tilt tests (70 degrees head-up for 2 min) were performed at 1, 6, 12, and 24 h of infusion. From 60 min before tilt, during tilt, and up to 15 min after end of tilt, ECG was monitored and BP, HR, and b/a ratio were recorded by means of fingertip plethysmography. Plasma-renin activity and concentrations of epinephrine and norepinephrine were measured preinfusion, and before and after tilt tests. Subjects were questioned frequently about adverse events. General tolerability of ISDN in the nine subjects who completed the study was poor, with eight suffering from headache and four from symptoms suggesting postural hypotension during tilt tests. Tolerability of ITF 296 was better, with 5 of 10 subjects reporting headache and 2 of 10 symptoms of postural hypotension during the first tilt only. Both active treatments successfully reduced DBP by at least 10% in all subjects at similar dose levels (final infusion rates 2.8 and 2.3 micrograms/kg/min for ITF 296 and ISDN, respectively). Systolic blood pressure (SBP) was reduced by about 6-7 mm Hg by both treatments. HR was increased by about 5 beats/min by ISDN but not by ITF 296. Those changes in BP and HR persisted throughout the 24-h infusion and reversed when it was discontinued. Fingertip plethysmography showed a profound reduction of b/a ratio, which persisted throughout the 24-h infusion. ISDN had consistently greater effects than ITF 296, suggesting that ISDN has the greater effects on small arterial vessels. Both active treatments reduced QS2 index throughout the 24-h period. Both treatments also reduced left-ventricular ejection time (LVET) index up to 3 h of infusion, with ISDN having the greater effects on LVET index and ITF 296 being intermediate between ISDN and placebo. ISDN prolonged pre-ejection period (PEP) at 1 h, had no effect at 2 h, and shortened PEP at 3 and 24 h. ITF 296 decreased PEP consistently during the 24-h infusion. Plasma-renin activity, epinephrine, and norepinephrine were increased by ISDN substantially more than by ITF 296. These results show that both ITF 296 and ISDN had comparable effects on diastolic blood pressure at similar dose-levels. ISDN increased HR, whereas ITF 296 did not. b/a Ratio was reduced more by ISDN, suggesting a greater activity on small arterial vessels. Arterial effects were maintained throughout the 24-h infusion. ISDN had a greater effect on venous return than ITF 296. ITF 296 seemed to show more balanced effects on preload and afterload than ISDN. ISDN caused significantly greater neurohumoral counter-regulation than ITF 296. Hemodynamic response to tilt was attenuated, as judged by the fact that hypotension occurred only during the early hours of the infusion, but the variability in the response of BP to tilt does not allow any firm conclusions to be drawn about possible development of tolerance. Tolerability of ISDN was poor and that of ITF 296 was better.