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1 The mode of action of hypotensive drugs is not necessarily the same early and late in a course of treatment. 2 It was aimed to study this possible difference of effects for the drugs debrisoquine and propranolol, using a clinical trial design and measuring as many cardiovascular functions as possible by noninvasive methods in out‐ patients. 3 Several well known effects of these drugs were noted; in addition it was found that in some subjects there was a small but progressive salt retention during propranolol treatment, that the displacements of the slopes in baroceptor function tests were different for the two drugs tested, and that venous distensibility was reduced at first with propranolol but soon increased again. 4 It is useful to combine longitudinal measures of body functions with a clinical trial when studying mechanisms of drug action.

1The interaction between phenylephrine and debrisoquine was studied using normal and hypertensive human volunteers, measuring blood pressure, pulse rate and pupil diameter. Single doses of phenylephrine were given before, during and after a short course of debrisoquine treatment.2 The circulatory effects of phenylephrine are potentiated by debrisoquine; in a few subjects this potentiation was marked and a potential hazard. 3 Limited deductions could be made about the effects of debrisoquine on baroceptor responses and adrenergic mechanisms.

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