Effect of 5,5'-diphenylhydantoin on the activities of hepatic cytosol malic enzyme and mitochondrial alpha-glycerophosphate dehydrogenase in athyreotic rats

Alteration of thyroid hormone homeostasis by antiepileptic drugs in humans: involvement of glucuronosyltransferase induction

RATIONALE

The aim of this review article is to analyse which antiepileptic drugs (AEDs) alter thyroid hormone homeostasis in humans and when this can be explained, at least partially, by the induction of the glucuronoconjugation pathways.

METHODS

Electronic databases were searched which have provided more than 300 articles. These have been integrated with fundamental books and personal information by experts in the different areas examined.

RESULTS

Alteration of thyroid hormone homeostasis by phenobarbital/primidone, phenytoin, and carbamazepine clearly occurs in humans. However, it is not associated with thyroid-stimulating hormone (TSH) increase and the clinical significance of altered serum concentrations of thyroid hormones by these antiepileptic drugs has remained unclear. The published information on the effect of the other antiepileptic drugs examined in this review article on thyroid hormones is lacking (felbamate, pregabalin, zonisamide) or limited. Oxcarbazepine appears to have some effects. Topiramate would need further investigations as well as gabapentin. Levetiracetam, tiagabine, vigabatrine, and lamotrigine do not alter at all, or only minimally, thyroid hormone homeostasis.

CONCLUSION

Concerning the antiepileptic drugs which alter thyroid hormone homeostasis, it is highly probable that the mechanism of induction of uridine diphosphate glucuronosyltransferases (UGT) is involved, at least partially, in such an alteration. However, it is not possible to estimate the relative contribution of the UGT induction by these drugs on the total alteration observed in thyroid hormone levels, as other mechanisms not investigated, or not examined in the present article, could contribute.

Furosemide, fenclofenac, diclofenac, mefenamic acid and meclofenamic acid inhibit specific T3 binding in isolated rat hepatic nuclei

Previous studies with phenytoin (DPH) show that this inhibitor of thyroid hormone binding to plasma proteins also interacts with specific nuclear T3 binding sites. In order to further define the nuclear effects of drugs that inhibit plasma protein binding of thyroid hormones, we assessed furosemide and a number of non-steroidal antiinflammatory drugs using isolated rat liver nuclei. The effects were compared with those of DPH, ipodate and amiodarone. The T3 binding site in isolated nuclei (Ka 1.2 X 10(9)M-1) showed relative affinity triac approximately equal to T3 greater than T4. Drugs were studied over the concentration range 10(-3)-10(-7)M, approximating the known therapeutic total plasma concentrations, in competition with 125I-T3 0.1 nM, expressing inhibition as the percent decrement from maximum specific binding of 125I-T3 in drug vehicle (assay buffer or thanol 1-10%). Specific T3 binding was inhibited by furosemide to 78.8 +/- 3.5% at 2 mM, by fenclofenac to 37.6 +/- 2.8% at 1 mM, by meclofenamic acid to 70.2 +/- 2.4% at 0.1 mM, by mefenamic acid to 60.6 +/- 4.6% at 0.05 mM (each p less than 0.02) and by diclofenac to 87.4 +/- 5.6% at 0.2 mM (p less than 0.05). In comparison, DPH inhibited T3 binding to only 88.1 +/- 0.6% at 0.3 mM, as did calcium ipodate (68 +/- 3.5% at 1 mM, p less than 0.02). Amiodarone (0.3 mM), sodium salicylate (1 mM) and phenylbutazone (0.1 mM) were inactive. In order to achieve a level of nuclear receptor occupancy that approaches in vivo occupancy, the concentration 125I-T3 was increased over the range 0.1-0.5 nM.2+t