Carbamazepine and risk of hypothyroidism: a prospective study.
OBJECTIVES - While carbamazepine (CBZ) decreases thyroid hormone concentrations it rarely causes hypothyroidism. We assessed prospectively the early effect of CBZ on thyroid status in thyroxine-supplemented hypothyroid patients, when compared with patients without a thyroid disorder. METHODS - In 29 patients, thyrotropin (TSH), total thyroxine (TT4) and free thyroxine (FT4) serum levels were assayed before starting CBZ, and then weekly for 7 weeks. Nineteen patients with no thyroid disorder (group A) were compared with 10 thyroxine-supplemented hypothyroid patients, stable before CBZ treatment (group B). RESULTS - In group A, TT4 decreased significantly by ca. 15-25%, starting from the first week (Friedman, P < 0.001). FT4 decline was smaller (ca. 10-15%) and delayed till the second week. FT4/TT4 ratio increased significantly (P < 0.001), while TSH only slightly (P = 0.073), never exceeding normal range. In group B, similar TT4 and FT4 decline was followed by significantly increasing TSH (P = 0.011), while the FT4/TT4 ratio was not significantly changed. In 3 of 10 patients TSH rose over 5 mIU/l, necessitating treatment adjustment. CONCLUSIONS - In patients with no thyroid disorder, CBZ causes hormonal changes of no clinical relevance, due to adaptive response. In T4-supplemented hypothyroid patients this adaptation is lacking, CBZ may precipitate subclinical or overt hypothyroidism, and early thyroid function monitoring seems advisable.
Simko
J
J
Department of Neurology, Charles University Prague, Facutly of Medicine and University Hospital, Hradec Kralove, Czech Republic.
Horacek
J
J
D000328:Adult; D000927:Anticonvulsants / Q000009:adverse effects; D002220:Carbamazepine / Q000009:adverse effects*; D003929:Diabetic Neuropathies / Q000188:drug therapy; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004827:Epilepsy / Q000188:drug therapy; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000139:chemically induced* / Q000503:physiopathology; D008657:Metabolic Clearance Rate / Q000187:drug effects / Q000502:physiology; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000592:standards; D011446:Prospective Studies; D012307:Risk Factors; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use; D014277:Trigeminal Neuralgia / Q000188:drug therapy
D000927:Anticonvulsants; D002220:Carbamazepine; D013972:Thyrotropin; D013974:Thyroxine