Abstract
Thirteen hypertensive patients entered a double-blind crossover trial of guanethidine and oxprenolol in combination. In nine patients who completed the trial there was an additive effect on blood pressure, but the combination had a smaller effect on heart rate than was expected from the individual effects, and side effects were not increased. During treatment with oxprenolol the plasma potassium concentration rose from 3.6 mmol (mEq)/1 to 3.9 mmol (mEq)/1. No correlation was found between the plasma oxprenolol concentration and changes in blood pressure or response to injected isoprenaline, but measurements of plasma oxprenolol concentrations were of value in determining compliance with the protocol.