Pharmacology and therapeutic applications of thyroxine

Hippokratia 1997, 1(2):73-82

F. Harsoulis, J. Gouni


Thyroxine (L-T4) is administered as substitution therapy in primary and secondary hypothyroidism as well as suppressive therapy in thyroid disease states like cold nodules, goiter and thyroid neoplasm. Substitution therapy requires titration of the dose based mainly on the serum TSH levels that have to be within the normal range. It is very important to establish from the beginning if the hyphothyroidism is permanent or transient and if a subclinical hypothyroidism will or will not become clinical and/or permanent. Thyroxine administration is absolutely necessary in neonatal hypothyroidism, where the most critical point is starting therapy as soon as possible. The suppression of goiter is successful more often in the diffuse than in multinodular form. The complete disappearance of a thyroid nodule after thyroxine treatment is quite rare, so the treating doctor must examine the data of each individual patient before surgery is recommended, as a definitive way to obtain a tissue diagnosis. If L-T4 should be administered in order to prevent recurrences of nodular goiters after lobectomy or subtotal thyroidectomy is questionable. In thyroid cancer, postoperatively, suppression of TSH by the administration of L-T4 is mandatory. The side-effects of L-T4, when the drug is misused can be serious because of the potential cardiotoxicity and the acceleration of osteoporosis, especially in postmenopausal women. Administration of L-T4 has no place in the treatment of obese euthyroid individuals