Prazosin once or twice daily?

In 20 patients with long-standing essential hypertension, a comparison was made in a randomized cross-over study of the effect of once and twice daily prazosin administration on blood pressure levels. Concurrent medication (beta-blocker and/or saluretic once daily) remained constant throughout the study. Blood pressure measurements were carried out by a nurse using a Hawksley random zero sphygmomanometer, both in the clinic and at home, and using a Roche Kontron Arteriosonde SR-2 at home. Observations made in the morning and in the evening showed no significant difference in blood pressure between the once and twice daily treatments. Eight patients complained of dizziness and faintness half an hour after taking the once daily dose. However, they felt quite well on the twice daily regimen. The mean daily dose in these 8 patients was prazosin 8.4 mg, range 6-12 mg. No indication was found that the subjective adverse side effects were correlated with the serum prazosin level. The complaints noted may possibly be overcome by taking the once daily dose late in the evening, just before retiring. Better still, the development of a slow-release formulation for daily dosages of 6 mg and over is suggested.