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 < 0.001) in supine and exercise heart rates and in sitting pulse rate. Serum triiodothyronine (T 3 ) fell (p < 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 < 0.001) and resting (r = 0.61, n = 14, p < 0.05) heart rates, percentage reduction in sitting pulse rate (r = 0.73, p < 0.001), and the percentage reduction in serum T 3 (r = 0.59, n = 23, p < 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 < 0.01). The plasma propranolol level correlated (r = 0.62, p < 0.01) with thyrotoxicosis therapeutic index. There was no correlation between degree of subjective improvement and plasma propranolol level. Clinical Pharmacology and Therapeutics (1980) 28, 40–44; doi: 10.1038/clpt.1980.128