Nifedipine gastrointestinal therapeutic system (GITS) for hypertensive patients in a primary care setting: results of the Extended Release Adalat Canadian Trial (EXACT).

Nifedipine gastrointestinal therapeutic system (GITS) is an extended-release dosage formulation that provides sustained blood concentrations of nifedipine over 24 hours. A 20-week, postmarketing surveillance study of the effectiveness and patient tolerability of nifedipine GITS 30 or 60 mg was conducted in the offices of 187 Canadian general practitioners from September 1992 to March 1994. A total of 1700 patients previously or newly diagnosed with mild-to-moderate essential hypertension (sitting diastolic blood pressure, 95 to 114 mm Hg) were included. The 20-week treatment period was completed by 1326 patients. Patients received nifedipine GITS 30 mg initially; the dose could be titrated upward to 60 mg after 3 and 6 weeks. Of all patients entered, 605 (35.6%) reported one or more adverse events. The three most frequently occurring adverse events were headache (12.2%), peripheral edema (8.1%), and dizziness (2.9%). The frequency of adverse events was highest in the first 3 weeks and decreased subsequently. The overall incidence of adverse events was 29.8% in patients receiving 30 mg of nifedipine GITS and 25.3% in those receiving 60 mg; adverse events were the cause of study discontinuation in 12.3% of patients. The overall health status of patients as measured by the SF-36 questionnaire was comparable to that previously reported for healthy individuals. At baseline, mean (+/- SE) systolic/diastolic blood pressure values for all patients were 160.1 +/- 0.4/97.4 +/- 0.2 mm Hg. Final blood pressure readings after 20 weeks of treatment in the 30-mg group (141.5 +/- 0.4/84.8 +/- 0.2 mm Hg) and the 60-mg group (146.6 +/- 0.8/88.8 +/- 0.4 mm Hg) were significantly decreased from baseline. At week 20, the 30-mg dose was sufficient to maintain blood pressure in 74.5% of patients; 25.5% of patients required 60 mg. Subgroup analysis revealed similar responses in patients who had received blood pressure medication before study initiation and those who had not. Response was also independent of age and type of previous antihypertensive therapy. In general medical practice, the 30-mg and 60-mg doses of nifedipine GITS were both effective and well tolerated and had minimal or no negative effects on the overall health status of treated individuals.