IS PLACEBO NECESSARY IN A STUDY OF DRUGS EFFECT ON AMBULATORY BLOOD-PRESSURE

Placebo has only a slight effect on ambulatory blood pressure (ABP). S ome authors have suggested that the use of a placebo is not necessary in a study on the drugs effect on ABP. We demonstrate that even if pla cebo effect is small, the use of a placebo group is still necessary. E ffects of one daily dose of 50 mg atenolol + 20 mg slow-released nifed ipine (AN) were investigated. Patients with office DBP 90-110 mmHg rec eived, in a double-blind protocol, either AN (group AN, n = 31) or a p lacebo (group P, n = 26). Ambulatory BP (ABP) and HR were measured (Sp acelabs or Diasys systems) for 24 h before and one month after treatme nt. The 2 groups were comparable before treatment. After 1 month under treatment, ABP was significantly lower in the AN group, compared to t he P group, and this over the whole day (p = 0.03 to p < 0.0001). The effect was the most important between 10-17 h (p < 0.0001). HR was sig nificantly lower in the AN group during daytime (6-22 h), but not duri ng the night (22-6 h). Over the whole group, placebo effect was not si gnificant. However, ABP did decrease under placebo in subjects with hi gh initial pressure. As a result, an analysis without data from the pl acebo group led to an overestimation of the effects of the drug.