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Related Experiment Videos

Thyroid hormone concentrations in epileptic patients.

J G Larkin1, G J Macphee, G H Beastall

  • 1University Department of Medicine, Western Infirmary, Glasgow, Scotland, UK.

European Journal of Clinical Pharmacology
|January 1, 1989
PubMed
Summary
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Anticonvulsant drugs can lower thyroid hormone levels, particularly total and free thyroxine (T4). Enzyme-inducing anticonvulsants like carbamazepine and phenytoin show this effect, unlike non-inducing sodium valproate.

Area of Science:

  • Endocrinology
  • Neurology
  • Pharmacology

Background:

  • Anticonvulsant medications are frequently associated with altered thyroid hormone levels.
  • Epileptic patients often require long-term anticonvulsant therapy, necessitating an understanding of potential side effects.

Purpose of the Study:

  • To investigate the impact of various anticonvulsant drugs on thyroid function in epileptic patients.
  • To differentiate the effects of enzyme-inducing versus non-enzyme-inducing anticonvulsants on thyroid hormone concentrations.

Main Methods:

  • Studied thyroid function in 54 epileptic patients on carbamazepine, phenytoin, sodium valproate, or polypharmacy.
  • Included 14 untreated epileptic patients and 11 healthy volunteers as controls.
  • Measured total thyroxine (T4), free thyroxine, tri-iodothyronine, and thyrotropin levels; conducted thyrotropin-releasing hormone stimulation tests.

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Main Results:

  • Total T4 concentrations were significantly reduced in patients taking enzyme-inducing drugs (carbamazepine, phenytoin) compared to controls and sodium valproate users.
  • Free T4 levels were also decreased in patients on carbamazepine and phenytoin.
  • Nine patients with T4 below the reference range were all on enzyme-inducing anticonvulsants.
  • Tri-iodothyronine and thyrotropin levels remained unaffected; TRH stimulation indicated no true hypothyroidism.
  • Sodium valproate, a non-inducing drug, did not lower T4 concentrations.

Conclusions:

  • Enzyme induction by anticonvulsant drugs is a likely mechanism for decreased serum total and free thyroxine concentrations in epileptic patients.
  • The findings highlight the differential effects of various anticonvulsants on thyroid hormone metabolism.
  • Monitoring thyroid function may be important for epileptic patients on enzyme-inducing anticonvulsant therapy.