Plasma protein binding of propranolol and isoprenaline in hyperthyroidism and hypothyroidism

1. The possibility that thyroid disease might result in alterations in the plasma proteins binding of drugs has been investigated by studying the binding of propranolol and isoprenaline in patients with hyperthyroidism and hypothyroidism. 2. Plasma protein binding of propranolol and isoprenaline has been measured in seven hyperthyroid patients and ten hypothyroid patients. Plasma binding was estimated by equilibrium dialysis at 37 degree C using triatiated propranolol and isoprenaline, both when the patients had thyroid dysfunction and again when they were euthyroid. 3. In the hyperthyroid group, mean propranolol binding varied from 86 +/- 1.7% when hyperthyroid to 88.4 +/- 0.8% when euthyroid. The comparable isoprenaline figures were 65.1 +/- 3.2% and 68.1 +/- 1.4% respectively. Neither difference was significant. 4. Isoprenaline binding was significantly lower (64.3 +/- 1.6%) when patients were hypothyroid than when they became euthyroid (68.8 +/- 1.2%). Propranolol binding was not altered by hypothyroidism. 5. It is concluded that clinically important alterations in free drug concentrations of propranolol or isoprenaline do not occur in hyperthyroidism or hypothyroidism.