Effects of thyroid dysfunction on propranolol kinetics

Propranolol kinetics was studied in six hyperthyroid and six hypothyroid patients who received single oral and intravenous doses of propranolol when they had thyroid dysfunction and again when they had become euthyroid. Change in thyroid status from hyperthyroid to euthyroid produced no change in the elimination half-life (t 1/2) of oral propranolol (3.2 +/- 0.5 to 4.1 +/- 0.7 hr), the oral clearance (38.4 +/- 7.3 to 27.4 +/- 2.4 ml/min/kg), the elimination t 1/2 of intravenous propranolol (2.5 +/- 0.3 to 3.5 +/- 0.7 hr), and the apparent volume of distribution (4.8 +/- 0.4 to 3.8 +/- 0.5 l/kg). The systemic clearance of propranolol, however, was greater when the patients were hyperthyroid (20.8 +/- 2.5 ml/min/kg) than when they had become euthyroid (11.7 +/- 1.7 ml/min/kg). The elimination t 1/2 after oral propranolol was longer in the hypothyroid (3.7 +/- 0.5 hr) than in the euthyroid state (2.0 +/- 0.1 hr). No other changes were observed in the kinetic parameters measured when these hypothyroid patients had become euthyroid. Adequate beta-adrenoceptor blockade in hyperthyroid patients may require higher propranolol dosage than expected.