Unusual malabsorption of levothyroxine

We report a 50-year-old woman, with overt hypothyroidism undergoing thyrotr opin (TSH)-stimulating hormone suppressive levothyroxine (LT4) treatment af ter subtotal thyroidectomy. At her first visit to our department, the labor atory results revealed a borderline low free thyroxine (FT4) level accompan ied by a clearly elevated TSH level. Both parameters did not significantly change during therapy with an oral dose of 500 mu g of LT4. Investigations revealed malabsorption of oral administrated LT4. Thyroid serum hormone lev els only became normal during parenteral therapy with LT4.