Efficacy and tolerability of tiapamil in patients with mild to moderate essential hypertension

Although early experience with tiapamil, a new calcium antagonist structurally related to verapamil, showed good antihypertensive efficacy and minimal adverse effects, recent studies have shown conflicting results. This single-blind dose-titration study was designed to determine the therapeutic efficacy, duration of action, and safety profile of tiapamil in patients with essential hypertension. After a 2-week washout period, patients received placebo for 4 weeks. Patients with a sitting diastolic blood pressure (SDBP) of 95-114 mm Hg received tiapamil 300 mg twice daily with dose increments of 150 mg twice daily every 2 weeks to a maximum of 1,200 mg/day. Once blood pressure (BP) control was achieved or patients were receiving 600 mg twice daily, they were followed up for an additional 2 weeks. Twenty of the initial 31 patients completed the trial, and 17 patients were receiving the highest dose of tiapamil. Nine patients dropped out because of adverse effects. No significant decreases in BP and heart rate (HR) were either noted by the clinic or apparent by 24-h ambulatory BP readings. Random assays of drug supplies showed that patients received the required dosage. The incidence of adverse effects rose with increasing doses of tiapamil: 27.6% of patients at 300 mg twice daily, 48% at 450 mg twice daily, and 81.8% at 600 mg twice daily. Dizziness, headache, and palpitations were the most frequent adverse effects. These results show that tiapamil given at a daily dose of 600-1,200 mg exhibits very little effect in lowering BP in patients with mild to moderate essential hypertension. Moreover, the incidence of adverse effects is much higher than reported in earlier studies.