Side effects of long-term oral anti-seizure drugs on thyroid hormones in patients with epilepsy: a systematic review and network meta-analysis

Introduction Anti-seizure drugs have long been known to affect thyroid hormone levels in epilepsy patients. The current study is a network meta-analysis designed to produce a systematic review and comprehensive evaluation of thyroid hormone changes to inform future research and clinical treatment. Method A systematic search of databases, PubMed, EMBASE, Web of Science, and the Cochrane Library, was conducted and all observational studies reporting thyroid hormone levels in epilepsy patients receiving monotherapy and controls were included. Stata MP.14 was used for analysis. Results A total of 35 studies, including 4135 participants and 8 anti-seizure drugs, were analyzed. TSH levels were elevated following use of topiramate [mean = 1.86; 95%CI: 0.83 to 2.90], levetiracetam [mean = 1.08; 95%CI: 0.07 to 2.09], and valproic acid [mean = 1.54; 95%CI: 0.58 to 2.50]. FT4 levels may be lowered by oxcarbazepine [mean = - 6.13; 95%CI: - 8.25 to - 4.02] and T4 was lowered by carbamazepine [mean = - 1.55; 95%CI: - 2.05 to - 1.05] and phenytoin [mean = - 1.33; 95%CI: - 1.80 to - 0.85]. No significant changes were reported for FT3, although use of phenobarbital resulted in a nonsignificant decrease [mean = - 0.31; 95%CI: - 0.99 to 0.37]. T3 levels were lowered by carbamazepine [mean = - 0.52; 95%CI: - 0.81 to - 0.24]. Lamotrigine had no significant effect on thyroid hormone levels. Conclusion Carbamazepine and phenytoin were the drugs most strongly associated with decreases in T4 and T3 levels while topiramate had the greatest elevating effect on TSH. Oxcarbazepine may lead to decreased serum FT4 and FT3, an effect relevant to central hypothyroidism. Phenobarbital appeared to significantly lower FT3. Use of levetiracetam and valproic acid may result in subclinical hypothyroidism. The anti-seizure drug with the least disruptive effect on thyroid hormone levels was found to be lamotrigine.