Propranolol dynamics in thyrotoxicosis.

Twenty-five thyrotoxic patients were treated with propranolol (160 mg/day) for 1 to 2 wk. Although the response to therapy varied there was a reduction (p less than 0.001) in supine and exercise heart rates and in sitting pulse rate. Serum triiodothyronine (T3) fell (p less than 0.001) and serum thyroxine did not change during propranolol therapy. Plasma propranolol levels before assessment varied from 5 to 121 ng/ml, and there were positive correlations between them and percentage reduction in exercise (r = 0.78, p less than 0.001) and resting (r = 0.61, n = 14, p less than 0.05) heart rates, percentage reduction in sitting pulse rate (r = 0.73, p less than 0.001), and the percentage reduction in serum T3 (r = 0.59, n = 23, p less than 0.01). Although weight loss ceased in the group as a whole the degree of continued weight loss or weight gain in individual patients was also related to plasma propranolol concentration (r = 0.61, p less than 0.01). The plasma propranolol level correlated (r = 0.62, p less than 0.01) with thyrotoxicosis therapeutic index. There was no correlation between degress of subjective improvement and plasma propranolol level.