Comparative anti-hypertensive effects of labetalol and the combination of oxprenolol and phentolamine.

1 The interaction of phentolamine with the beta-adrenoreceptor-blocking drug, oxprenolol, was studied in a controlled trial. 2 The combination was generally well tolerated. 3 Oxprenolol alone produced modest but significant reductions in supine, standing and post-exercise blood pressures. Small reductions were observed only with sustained phentolamine administration. 4 The combined effect of the two drugs seemed to be addictive only at the lower level of oxyprenolol dosage. 5 Labetalol produced significantly greater reductions in supine and standing blood pressure than combined oxprenolol-phentolamine. At a daily dose of 400 mg, postural hypotension was not observed, although transient symptoms were frequent.