Animal studies have suggested that tetracyclines may exert an antithyroid action, although reports have been contradictory.1-5 The effect of tetracycline therapy on the human thyroid has not been investigated. Because of the obvious clinical importance of documenting any antithyroid effects in man, a study of thyroid function was undertaken before and following 11 consecutive days of tetracycline hydrochloride administration.
Method and Materials
Fourteen ambulatory male patient volunteers between the ages of 36 and 67 years were given 2 gm daily of tetracycline hydrochloride (Achromycin V) orally in four divided doses for a period of 11 days. Each patient served as his own control. Those patients selected were not acutely ill or debilitated, had no evidence of thyroid, renal or hepatic disease, or congestive heart failure, and had no recent intake of diagnostic or therapeutic iodides. Prior to tetracycline treatment, blood was drawn for duplicate protein-bound iodine (PBI) and cholesterol
Becker KL, Katz S, Miale A. Tetracycline and Thyroid Function. JAMA. 1967;199(6):416–417. doi:10.1001/jama.1967.03120060114022