Impairment of isoniazid clearance by propranolol

The effect of propranolol on isoniazid elimination kinetics have been investigated in six healthy males. Following propranolol pretreatment of 40 mg at 8-hourly intervals given for three days, isoniazid clearance (13.0 l/hour +/- s.e.m. 2.6 l/hour) was significantly lower (p less than 0.01) than that obtained during the control study (16.4 l/hour +/- s.e.m. 3.0 l/hour). However, no significant correlation was demonstrated between the magnitude of the reduction in isoniazid clearance and the depression of the exercise-induced tachycardia caused by propranolol (rs = 0.03, p greater than 0.05). The mechanism of the impairment of isoniazid clearance by propranolol is unlikely due to the change in liver blood flow.