ABSTRACT
INTRODUCTION: The non-adherence to substitutive treatment by L-thyroxine is the main cause of the discordance between high thyrotropin values and high doses of the drug. OBSERVATION: In a 36-year-old patient with post-surgery hypothyroidism, thyrotropin values ranged between 100 and 400 mUI/L, although daily replacement therapy included 300 µg of L-thyroxine and 75 µg of L-triiodothyronine. The oral loading test with L-thyroxine was normal and thyrotropin serum level returned to normal values under weekly oral administration of 1000 µg L-thyroxine. CONCLUSION: The strategy of non-adherence treatment in hypothyroidism is well defined with oral testing of L-thyroxine, followed by oral or parenteral weekly administration of the drug. The L-thyroxine oral test is the gold standard for diagnosis after eliminating of the other conventional causes: drug interactions or digestive malabsorption. L-thyroxine treatment should be discussed on a case-by-case basis, either daily under surveillance or once weekly oral or parenteral high dose.
