Apparent increase in type I 5'-deiodinase activity induced by antiepileptic medication in mentally retarded subjects.
OBJECTIVE
Thyroid function measurements in 3 mentally retarded patients treated with antiepileptic drugs (phenytoin or carbamazepine) showed normal thyroid-stimulating hormone (TSH) responses in spite of markedly low levels of total thyroxine (T(4)), triiodothyronine (T(3)), and free thyroxine (FT(4)) concentrations; free triiodothyronine (FT(3)), as well as mean thyroxine-binding globulin (TBG) concentrations were normal. The objective of the present investigations was to determine if antiepileptic medication in these patients contributed to the disparate TSH and thyroid hormone (TH) levels.


METHODS
Thyroid tests and other laboratory parameters were measured by conventional techniques.


RESULTS
Circulating TH changes noted in retarded patients were similar to those observed in control subjects receiving carbamazepine alone. Reverse T(3) (rT(3)) levels in all patients were either undetectable or below the normal range.


CONCLUSIONS
As type I 5'-deiodinase has a higher affinity for rT(3) than T(4), an increased activity of this enzyme would enhance rT(3) deiodination and reduce serum rT(3) concentration whereas enhanced T(4) deiodination would aid in normalizing intracellular FT(3) concentration. The finding of normal serum FT(3) concentration was consistent with normal TSH response and clinical euthyroidism in both retarded and control subjects. While phenytoin-induced increase in type I 5'-deiodinase has been previously noted, the present studies demonstrate a similar effect of carbamazepine on 5'-deiodinase.
Premachandra
B N
BN
Thyroid Specialty Laboratory, St Louis, Mo 63125, USA.
Radparvar
A
A
Burman
K
K
Williams
I K
IK
D000328:Adult; D000927:Anticonvulsants / Q000009:adverse effects* / Q000627:therapeutic use; D002220:Carbamazepine / Q000009:adverse effects / Q000627:therapeutic use; D005260:Female; D006728:Hormones / Q000097:blood; D006801:Humans; D008607:Intellectual Disability / Q000150:complications*; D007453:Iodide Peroxidase / Q000097:blood*; D008297:Male; D010672:Phenytoin / Q000009:adverse effects / Q000627:therapeutic use; D012640:Seizures / Q000150:complications / Q000188:drug therapy; D013960:Thyroid Function Tests; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000097:blood; D014285:Triiodothyronine, Reverse / Q000097:blood
D000927:Anticonvulsants; D006728:Hormones; D013963:Thyroid Hormones; D002220:Carbamazepine; D014285:Triiodothyronine, Reverse; D013973:Thyrotropin-Releasing Hormone; D010672:Phenytoin; D013972:Thyrotropin; C109812:iodothyronine deiodinase type I; D007453:Iodide Peroxidase