Treatment with Intramuscular Levothyroxine in Refractory Hypothyroidism

Abstract

Introduction: Orally and daily levothyroxine (LT4) is the treatment of choice for hypothyroidism. In the majority of cases, the lack of effectiveness by this way may be due to poor adherence; however, gastrointestinal malabsorption may explain more cases of thyroxine refractoriness than previously reputed, due to the number of occult forms of these disorders.

Case presentation: A 55-year-old white man with a diagnosis of low risk of recurrence of follicular variant of papillary thyroid carcinoma was treated with total thyroidectomy, 30 mCi iodine 131, and oral LT4. A year before he presented a gastric adenocarcinoma that required a partial gastrectomy. He evolved with multiple episodes of intestinal subocclusion that had to be treated with enterectomy in the first instance, then digestive rest and total parenteral nutrition. In spite of having made increases in oral LT4 dose (3 µg/kg), the patient persisted with a thyroid-stimulating hormone level >100 mIU/L. For this reason, we decided to administer intramuscular LT4.

Conclusion: Since there are no guidelines or consensus of intramuscular LT4 use, our experience and how we decided the dose and way of administration are presented in this article to contribute to future cases.

Keywords: Intramuscular levothyroxine; Levothyroxine therapy; Refractory hypothyroidism.

Fig. 1

FT4 and TT4 levels after administration of 200 and 400 μg of intramuscular LT4. *200 μg of intramuscular LT4. **400 μg of intramuscular LT4. FT4, free thyroxine; LT4, levothyroxine; TT4, total thyroxine.