The Effect of Single‐Dose Phenylpropanolamine on Blood Pressure in Patients with Hypertension Controlled by β Blockers

We studied the effect of phenylpropanolamine on blood pressures in seven patients whose hypertension was controlled with β blockers. Rapid‐release phenylpropanolamine 25 mg and placebo were given on separate days according to a double‐blind, randomized, two‐period crossover design. The crossover analyses detected significant drug effects without carryover or period effects for both systolic and diastolic pressures. The peak systolic blood pressures after phenylpropanolamine averaged 8 mm Hg higher than those measured after placebo. Similarly, the peak diastolic pressures after phenylpropanolamine averaged 4.9 mm Hg higher than those with placebo. Baseline weights, blood pressures, and pulses did not significantly differ between patient groups or change significantly across study periods. Usual single and therapeutic doses of phenylpropanolamine caused small but statistically significant increases in blood pressure. If such changes are not considered when antihypertensive therapy is altered or initiated, patients may receive excessive or unnecessary drugs. 1990 Pharmacotherapy Publications Inc.