Antihypertensive Effect of a New Formulation of Slow Release Oxprenolol in Essential Hypertension

To test whether a new formulation of a slow release oxprenolol (SLOx) can produce a steady 24-h antihypertensive effect, we recorded 24-h intraarterial blood pressure (Oxford technique) in eight ambulant in-patients (age 44.5 ± 3.0 years, mean ± SE) with a mild or moderate hypertension who were untreated since three weeks. The study was started seven days after hospitalization and was conducted according to a randomized doubleblind cross-over design. Blood pressure recordings were made after (a) a 7-day administration of SLOx in a single evening dose, and (b) a 7-day administration of placebo. This design allowed to determine the effect of SLOx without interference from nonspecific blood pressure lowering factors. Blood pressure effects of handgrip, submaximal cyclette exercise, and cold pressor test 20–24 h after the administration of SLOx and placebo were also evaluated. The blood pressure tracing was analyzed beat-to-beat by a computer which provided also the analysis of the heart rate data. The 24-h mean systolic and diastolic blood pressure measured during placebo were 144.6 ± 6.4 and 81.1 ± 3.9 mm Hg, the corresponding heart rate being 76.9 ± 3.5 beats/min. SLOx reduced these values by 6.2, 10.6. and 4.8, respectively, all effects being similarly evident throughout the blood pressure recording. The pressor responses to handgrip, cyclette exercise, and cold pressor test were not affected by SLOx. By contrast, the small tachycardic response to handgrip and the large tachycardic response to submaximal cyclette exercise were significantly reduced by the drug. Due to the lower baseline values, the absolute blood pressure and heart rate observed during each test were significantly lower with SLOx than with placebo. Thus a single daily dose of SLOx can lower blood pressure and heart rate of hypertensive patients throughout the 24 h even when these variables are subjected to the excitatory effects of exercise and stress.