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Patients with hypothyroidism who are treated with the antitumor drug imatinib need more thyroxine
The background of the study. Imatinib mesylate
(Gleevec) is a drug used to treat patients with leukemia and other
tumors, and it is being given experimentally to patients with medullary
thyroid carcinoma. In this study, patients with hypothyroidism were
found to need higher doses of thyroxine (T4) when treated with imatinib.
How the study was done. Serum thyrotropin (TSH) and free thyroxine were measured repeatedly in 10 patients with medullary thyroid carcinoma and in 1 patient with a gastrointestinal stromal-cell tumor during treatment with imatinib. Eight of the patients had hypothyroidism after thyroid surgery and were taking thyroxine (T4) and 3 had normal thyroid function. The dose of T4 was raised if needed to maintain normal serum TSH values.
The results of the study. Before imatinib therapy, the patients with hypothyroidism had low or normal serum TSH and normal serum free T4 concentrations while taking 100 to 225 µg of T4 daily. During imatinib therapy, these eight patients had symptoms of hypothyroidism, higher serum TSH concentrations, and lower serum free T4 concentrations. Their dose of T4 was increased by 33 percent after 12 to 16 weeks and 47 percent after 26 to 32 weeks. The three patients who had normal thyroid function had no change in serum TSH or free T4 concentrations during imatinib therapy.
The conclusions of the study. The anticancer drug imatinib increases the need for T4 in patients with hypothyroidism, probably because the drug increases T4 clearance.
The original article. De Groot JW, Zonnenberg
BA, Plukker JT, van Der Graaf WT, Links TP. Imatinib induces hypothyroidism
in patients receiving levothyroxine. Clin Pharmacol Ther 2005:78:433-
8.
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| Thyroid Digest Index | | | November 2005 Thyroid Digest |
