Indoramin and prazosin as adjuncts to beta adrenoceptor blockade in hypertension

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Abstract
Two trials were conducted on the effects of adding alpha‐adrenoreceptor blockers to the therapy of hypertensive patients already receiving a beta‐adrenoreceptor blocking drug with or without a diuretic. The first trial was a single‐blind study in which 6 patients receiving long‐term combination therapy were crossed from prazosin, 6 to 15 mg/day, to a dose of indoramin 10 times as large. There was significant bradycardia but little change in blood pressure. The second trial was a double‐blind randomized crossover study in which 15 patients completed an 8‐wk period of treatment with each of the alpha blockers, administered in random sequence with an intervening 2‐wk washout period. Dosage was titrated for optimal antihypertensive effect. The final mean dosages were 76 mg/day for indoramin and 8.2 mg/day for prazosin; the dose ratio was 9.3:1. Both drugs reduced erect systolic blood pressure. Prazosin, but not indoramin, reduced exercise systolic and diastolic pressures. Indoramin lowered supine and exercise pulse rates. Neither drug affected peak expiratory flow rate or plasma renin activity. Analysis of individual responses in supine diastolic blood pressure showed that there were 9 prazosin and 8 indoramin responders, while 9 of the 21 subjects in the 2 trials failed to respond to either drug. Central side effects were more prominent with indoramin. The combination of one or other of these alpha‐adrenoreceptor blockers with preexisting beta‐adrenoreceptor blockade improved blood pressure control in 57% of the patients.