Role of colestipol in the treatment of hyperthyroidism

The enterohepatic circulation of thyroxine (T₄) and triiodothyronine (T₃) is higher in thyrotoxicosis. Bile-salt sequestrants bind iodothyronines and thereby increase their fecal excretion. We, therefore, evaluated the effect of colestipol-hydrochloride administration on clinical and biochemical indices of patients with hyperthyroidism. In a prospective, controlled trial, ninety-two adult volunteers with Graves' disease, toxic autonomous nodule or toxic multinodular goiter were randomly assigned into the following treatment protocols: Group 1, 30 mg of methimazole (MMI) and 20 g of colestipol-hydrochloride (COL) daily; Group 2, 30 mg of MMI daily; and Group 3, 15 mg of MMI 20 g of COL daily. The patients were further classified into Group A, severe hyperthyroidism (baseline levels of total T₃ (TT₃) ≥ 5 nmol/l) and Group B, mild to moderate thyrotoxicosis (baseline levels of TT₃ < 5 nmol/l). Crook's clinical index, serum free T₄ (FT₄), TT₃ and thyroid stimulating hormone (TSH) levels were determined before (W0), following one week (W1) and two weeks (W2) of treatment. Serum TT₃ level decreased (mean ± SE) at W1 by 40.8 ± 2.6% of W0 in Group 1 and by 29.2 ± 2.4% in Group 2 (p < 0.001), and down further to 47.8 ± 3.0% at W2 in Group 1, and 40.6 ± 2.8% in Group 2 (p = 0.01). Serum FT₄ level decreased (mean ± SE) from W0 to W1 by 31.7 ± 2.7% in Group 1 and by 16.2 ± 3.1% in Group 2 (p = 0.005), and down to 49.1 ± 2.8% of W0 at W2 in Group 1 and to 38.7 ± 3.5% in Group 2 (p = 0.07). In sub groups B COL was not effective in reducing thyroid hormone levels nor in ameliorating the clinical status of the patients. However, in Group A3 COL lowered FT₄ (p = 0.001) and TT₃ (p = 0.05) levels as compared to group A2. At W2 the clinical hyperthyroidism score improved faster in Group A1 (p < 0.001) and Group A3 (p = 0.012) as compared to the control Group A2. In conclusion, COL is an effective and well tolerated adjunctive agent in the treatment of hyperthyroidism. Its main effect is in severe cases of thyrotoxicosis, and in the first phase of treatment. As adjunctive COL treatment in hyperthyroidism allows reducing MMI dosage it may decrease the rate of dose dependent MMI side effects.