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.