Nifedipine GITS (Gastro-Intestinal Therapeutic System) is a recently launched long-acting formulation of nifedipine. The aim of the Italian Nifedipine GITS Study was to determine the duration of the antihypertensive effect of once-daily nifedipine GITS in outpatients with essential hypertension. After a 2-week placebo run-in period, 126 patients with mild to moderate essential hypertension (diastolic BP95 to 114mm Hg) were randomised to receive nifedipine GITS 30mg (n = 42), nifedipine GITS 60mg (n = 42) or placebo (n = 42), once daily in a double-blind fashion for 4 weeks. At the end of the run-in and treatment periods, ambulatory BP monitoring was performed (Spacelabs 90202 or 90207 device) to provide regular 15-minute BP readings for 24 to 36 hours.
In the 81 patients with at least 24 hours of valid ambulatory BP data, the average systolic and diastolic BP changes after treatment with nifedipine GITS 30mg (n = 25), nifedipine GITS 60mg (n = 28) and placebo (n = 28) were - 16.5/-10.8. -16.3/-10.0 and +0.4/+0.9mm Hg, respectively. BP changes with nifedipine GITS differed significantly (p < 0.01) from those with placebo. Heart rate was not significantly altered by nifedipine GITS. The effects of nifedipine GITS and placebo on ambulatory BP 24 hours and 36 hours after the last dose were evaluated in 56 patients with complete 36-hour ambulatory BP profiles. After 24 hours, both doses of nifedipine GITS caused significant (p < 0.01) reductions in systolic and diastolic BP. After 36 hours, the reduction in ambulatory BP induced by nifedipine GITS was less pronounced than after 24 hours; the changes in systolic BP produced by both nifedipine GITS doses were still significant (p < 0.01), whereas the change in diastolic BP was significant only after the 60mg dose (p < 0.05).
Trough : peak ratios of the antihypertensive effect of nifedipine GITS were calculated by comparing the highest average hourly BP reduction between 2 and 6 hours postdose (peak reduction) and the BP change at 24 hours postdose (trough reduction) in the 81 patients with valid 24-hour ambulatory BP data. Trough : peak ratios were 90.5% (systolic BP) and 76.3% (diastolic BP) for nifedipine GITS 30mg, and 109.3% (systolic BP) and 98.6% (diastolic BP) for nifedipine GITS 60mg. The ratios were further increased if placebo-induced BP changes were taken into account.
In conclusion, the antihypertensive effect of nifedipine GITS is maintained for more than 24 hours postdose, and is uniform over this period, without any undue imbalance between the peak BP effect and that observed immediately before the subsequent dose.