No effect of ketoconazole on thyroid function of normals and thyrotoxic patients

To investigate a putative inhibitory effect of the antifungal agent ketoconazole on thyroid function, five patients with thyrotoxicosis and ten normal subjects were treated with ketoconazole at high doses (600 mg daily in three 200 mg oral doses) for four weeks. TSH, TT3, TT4FT3 and FT4 were measured before and after the end of treatment. In all of the normal subjects no significant modifications of circulating thyroid hormones and TSH were detected. In patients with thyrotoxicosis an increase of the levels of circulating thyroid hormones and a worsening of clinical signs were observed. However, this behaviour could not be related to an action of the drug since it not differ from the normal evolution of untreated hyperfunctional thyroid disease. These findings confirm the lack of any inhibitory effect of ketoconazole on the synthesis of thyroid hormones and thyroid function.