Comparison of effects of two dosage regimens of phenylpropanolamine on blood pressure and plasma levels in normal subjects under steady-state conditions.

Plasma levels and blood pressure responses to two dosage regimens of phenylpropanolamine (PPA)-25-mg, immediate-release tablets three times per day and a 75-mg, controlled-release capsule once per day--were compared in 14 normal subjects. To obtain steady-state conditions, subjects were given the test materials for four-day periods, and blood pressure and plasma PPA levels were measured on day 4. The dosage forms were equally bioavailable, based on a 95-percent confidence coefficient, and neither produced hypertensive effects. The highest diastolic pressure was 96 mm Hg three hours after a 25-mg dose. Mean PPA plasma levels showed no correlation with mean blood pressure readings at any point during a 12-hour test period. These data show that, in these subjects, a daily dosage of PPA 75 mg, either in divided doses of 25 mg each or in a dependable controlled-release formula, produces no indication of pressor effects.