Clonidine and the vasodilating beta blocker antihypertensive drug interaction.

Because propranolol is contraindicated in some patients and since clonidine can decrease heart rate and renin release, clonidine was substituted for propranolol in 14 severely hypertensive minoxidil-treated outpatients. Clonidine induced weight loss which, since plasma concentrations were not suppressed, was not due to inhibition of release of antidiuretic hormone or renin. These endocrine interrelations were confirmed by later administration of clonidine to 4 of the subjects under controlled circumstances in our General Clinical Research Center. When substituted for propranolol, clonidine controlled blood pressure and heart rate in 8 of the 9 outpatients whose blood pressure had been previously well controlled. Clonidine and propranolol had additive antihypertensive effects in the other 5 patients. Thus, clonidine can substitute for propranolol or when added to the propranolol-vasodilator combination supply an additional blood pressure-lowering effects. This substitution or addition results in an increase in side effects. In addition, clonidine has a diuretic action under these circumstances by an unknown mechanism.