Unusual malabsorption of levothyroxine.

We report a 50-year-old woman, with overt hypothyroidism undergoing thyrotropin (TSH)-stimulating hormone suppressive levothyroxine (LT4) treatment after subtotal thyroidectomy. At her first visit to our department, the laboratory results revealed a borderline low free thyroxine (FT4) level accompanied by a clearly elevated TSH level. Both parameters did not significantly change during therapy with an oral dose of 500 microg of LT4. Investigations revealed malabsorption of oral administrated LT4. Thyroid serum hormone levels only became normal during parenteral therapy with LT4.