Thyroid hormone levels in children receiving carbamazepine or valproate

Effect of Valproate Monotherapy on Thyroid Function Tests and Magnesium Levels in Children With Epilepsy

BACKGROUND

Antiseizure drug valproate alters thyroid functions. Magnesium is implicated in the pathogenesis of epilepsy and it may affect the efficacy of valproate and thyroid functions.

OBJECTIVE

To study the effect of six months of valproate monotherapy on thyroid functions and serum magnesium levels. To study the association among these levels and the effects of clinicodemographic profile.

MATERIALS AND METHOD

Children aged three to 12 years presenting with newly diagnosed epilepsy were enrolled. A venous blood sample was collected for estimation of thyroid function test (TFT), magnesium, and valproate levels at onset and after six months of valproate monotherapy. Valproate levels and TFT were analyzed by chemiluminescence and magnesium by colorimetric method.

RESULTS

Thyroid stimulating hormone (TSH) increased significantly from 2.14±1.64 µIU/ml at enrollment to 3.64±2.15 µIU/ml at six months (p<0.001), free thyroxine (FT4) decreased significantly (p<0.001). Serum magnesium (Mg) decreased from 2.30±0.29 mg/dl to 1.94±0.28 mg/dl (p<0.001). At six months, eight out of 45 (17.77%) participants had significantly increased mean TSH levels (p=0.008). Serum valproate levels were not associated significantly with TFT and Mg (p<0.05). There was no effect of age, sex, or repeat seizures on the measured parameters.

CONCLUSION

The TFT and Mg levels are altered by six months of valproate monotherapy in children with epilepsy. Hence we suggest monitoring and supplementation if required.

Thyroid functions as a parameter in monitoring of antiepileptic drugs

INTRODUCTION

Epilepsy is a chronic neurological disorder that is treated with multiple medications that can have significant side effects. This study investigated the potential effects of antiepileptic drugs on thyroid function.

METHODS

The participants in this study were epileptic adults who had been consistently monitored in follow-up care. The effects of antiepileptic drugs on the serum levels of the thyroid stimulating hormone (TSH), free T3 (fT3), and free T4 (fT4) of these patients were investigated retrospectively by comparing laboratory recordings in three defined periods: prior to antiepileptic drug treatment, between 6 months and 1 year of treatment (early stage), and after 1 year of treatment (late stage).

RESULTS

  A total of 300 epileptic patients (F/M: 175/125) were included in the study. Significant differences in TSH and fT4 serum levels in the late stage compared to the pre-treatment stage (p = 0.006 and p = 0.0005, respectively) were found. TSH values in the late stage of treatment were abnormally high in one case and low in five cases; all six of these cases had normal pre-treatment and early-stage TSH values. Patients who received monotherapy with valproic acid, levetiracetam or carbamazepine were evaluated separately and there was no statistically significant difference in TSH and fT3 levels, while fT4 levels were significantly increased during treatment in each treatment group.

CONCLUSIONS

A significant increase in TSH levels was found in epileptic patients on polytherapy. Our results give us the opportunity to highlight the potential unique or cumulative effect of antiepileptic drugs on thyroid hormone levels.

Is the prevalence of thyroid disease higher in children receiving antiepileptic medication? A systematic review and meta-analysis

PURPOSE

Antiseizure medications (ASM) have long been examined for their potential to induce thyroid dysfunction. The aim of this systematic review and meta-analysis was to assess the prevalence of thyroid disease in children up to 16 years receiving monotherapy with valproate (VPA), carbamazepine (CBZ) and levetiracetam (LEV).

METHODS

PubMed/MEDLINE, Cochrane/CENTRAL databases and the gray literature were searched to identify observational studies providing the prevalence of thyroid dysfunction in the target population under VPA, CBZ, or LEV monotherapy schemes. The results were pooled using a random-effects model, and additional subgroup analyses were performed for the three ASM groups.

RESULTS

Fifteen and thirteen studies met inclusion criteria for the qualitative and the quantitative analysis, respectively, with a total of 945 pediatric patients with prevalence data. Only VPA and CBZ were associated with thyroid dysfunction. The overall prevalence of thyroid abnormality was higher in children receiving ASM [odds ratio (OR) 6.82, 95% confidence interval (CI) 3.96-11.75]. In the subgroup analysis, the prevalence of biochemical thyroid abnormality with increased TSH was higher in the VPA (OR 9.54, 95%CI 5.25-17.34) and the CBZ group (OR 4.08, 95%CI 1.84-9.04) compared with controls.

CONCLUSION

This study confirms the higher prevalence of biochemical thyroid abnormality in children under VPA and CBZ monotherapy, whereas no such evidence is present for LEV. In children with a predisposition for thyroid disease, LEV should be considered over VPA and CBZ, if appropriate for seizure type and epilepsy syndrome. More studies are needed to reach a consensus on monitoring and management of thyroid dysfunction in children receiving ASM therapy.

Antiseizure medications and thyroid hormone homeostasis: Literature review and practical guideline

Thyroid hormones play an essential role in central nervous system development, normal physiological brain function, and repair mechanisms. On one hand, thyroid hormone alterations influence cortical excitability, and on the other hand antiseizure medications (ASMs) are associated with alterations in thyroid hormone metabolism. Although this interaction has long been described, and epilepsy is a common and chronic neurological disease, studies describing the interplay are often small and retrospective. We performed a systematic review of the current literature on epilepsy, ASMs, and thyroid hormone metabolism. Forty-seven studies were included. Most studies were retrospective cross-sectional studies (n = 25) and investigated thyroid function alterations in patients on older ASMs such as phenobarbital, phenytoin, carbamazepine, and valproate. Overall, almost one third of patients with epilepsy had thyroid hormone alterations, especially patients on valproate (25%) and carbamazepine (10%-25%). Studies with patients receiving polytherapy are scarce, but reported a higher risk for hypothyroidism in patients with older age (p = .004), female sex (p = .014), longer duration of epilepsy (p = .001), intractable epilepsy (p = .009), and polytherapy. Studies on newer ASMs are also limited, and further studies on an interplay with thyroid hormone homeostasis are essential to improve the care for epilepsy patients. ASMs are associated with alterations in thyroid hormone metabolism. Thyroid function monitoring is indicated in patients on ASMs, especially those with refractory epilepsy and those on polytherapy. We provide a practical guideline for thyroid function monitoring for the clinician taking care of patients on ASMs.

Hypothyroidism induced by phenytoin and gabapentin: A Case Report

RATIONALE

Antiepileptic drugs (AEDs) are one of the causative drugs of drug-induced hypothyroidism. In most cases, AED-induced hypothyroidism is subclinical and indicated only by abnormalities of free thyroxine (T4) and/or thyroid-stimulating hormone (TSH) levels. Severe symptomatic hypothyroidism following AEDs is rarely reported in the literature.

PATIENT CONCERNS

A 75-year-old man experienced neurologic symptoms including memory impairment, ataxic gait, sensory polyneuropathy and myopathy, lethargy, and edema of the face and lower extremities. He had been administered phenytoin and gabapentin for the treatment of symptomatic traumatic epilepsy 8 years before.

DIAGNOSES

The patient had low free T4 (0.21 ng/dL) and high TSH (113.2 μIU/mL), which indicated hypothyroidism. Negative thyroid-related autoantibody tests and the lack of goiter excluded the possibility of Hashimoto disease. Phenytoin and/or gabapentin were strongly suspected as causing his hypothyroidism.

INTERVENTION

The patient was treated with replacement therapy (levothyroxine 25 μg/day).

OUTCOMES

His symptoms markedly and promptly improved alongside continued antiepileptic therapy.

LESSONS

In this case, the patient's hypothyroidism was assumed to result from different mechanisms of the 2 AEDs leading to thyroid hormone reduction. AEDs can not only cause asymptomatic thyroid hormone abnormalities but also clinically observable hypothyroidism. Therefore, clinicians should be aware of the association between anticonvulsants and symptomatic hypothyroidism.

Human relevance of follicular thyroid tumors in rodents caused by non-genotoxic substances

Chronic stimulation of the thyroid gland of rodents by TSH leads to thyroid follicular hyperplasia and subsequently to thyroid follicular adenomas and carcinomas. However, the interpretations of rodent thyroid tumors are contradictory. The U.S. Food and Drug Administration (FDA) concluded that findings with drugs that lead to increased levels of thyroid-stimulating hormone (TSH) in rats are not relevant to humans, whereas the U.S. Environmental Protection Agency (US EPA) concluded that chemicals that produce rodent thyroid tumors may pose a carcinogenic hazard for humans although the thyroid of rodents appears to be more sensitive to a carcinogenic stimulus than that of humans. Meanwhile, based on the CLP Criteria of the European Chemicals Agency (ECHA), rodent thyroid tumors caused by the induction of uridine-diphosphate-glucuronosyl transferases (UDGT) were assessed as not relevant to humans. To clarify these discrepant positions, the function and regulation of the thyroid gland are described and the types of thyroid tumors and the causes of their development in humans and animals are examined. Based on these data and the evidence that so far, except radiation, no chemical is known to increase the incidence of thyroid tumors in humans, it is concluded that rodent thyroid tumors resulting from continuous stimulation of the thyroid gland by increased TSH levels are not relevant to humans. Consequently, compounds that induce such tumors do not warrant classification as carcinogenic.

Hypothyroidism risk compared among nine common bipolar disorder therapies in a large US cohort

OBJECTIVES

Thyroid abnormalities in patients with bipolar disorder (BD) have been linked to lithium treatment for decades, yet other drugs have been less well studied. Our objective was to compare hypothyroidism risk for lithium versus the anticonvulsants and second-generation antipsychotics commonly prescribed for BD.

METHODS

Administrative claims data on 24,574 patients with BD were analyzed with competing risk survival analysis. Inclusion criteria were (i) one year of no prior hypothyroid diagnosis nor BD drug treatment, (ii) followed by at least one thyroid test during BD monotherapy on lithium carbonate, mood-stabilizing anticonvulsants (lamotrigine, valproate, oxcarbazepine, or carbamazepine) or antipsychotics (aripiprazole, olanzapine, risperidone, or quetiapine). The outcome was cumulative incidence of hypothyroidism per drug, in the presence of the competing risk of ending monotherapy, adjusted for age, sex, physician visits, and thyroid tests.

RESULTS

Adjusting for covariates, the four-year cumulative risk of hypothyroidism for lithium (8.8%) was 1.39-fold that of the lowest risk therapy, oxcarbazepine (6.3%). Lithium was non-statistically significantly different from quetiapine. While lithium conferred a higher risk when compared to all other treatments combined as a group, hypothyroidism risk error bars overlapped for all drugs. Treatment (p = 3.86e-3), age (p = 6.91e-10), sex (p = 3.93e-7), and thyroid testing (p = 2.79e-87) affected risk. Patients taking lithium were tested for hypothyroidism 2.26-3.05 times more frequently than those on other treatments.

CONCLUSIONS

Thyroid abnormalities occur frequently in patients with BD regardless of treatment. Therefore, patients should be regularly tested for clinical or subclinical thyroid abnormalities on all therapies and treated as indicated to prevent adverse effects of hormone imbalances on mood.

Effects of long-term valproic acid treatment on hematological and biochemical parameters in adolescent psychiatric inpatients: a retrospective naturalistic study

The objective of this study was to determine the long-term hematological and biochemical side effects of valproic acid (VPA) in psychiatric adolescent inpatients. A retrospective naturalistic study design was used. Participants were psychiatric inpatients treated with VPA, alone or in combination with other medications. Electronic medical files were reviewed for changes in hematological and biochemical parameters following a course of VPA treatment. One hundred and four adolescents aged 12-18 (mean 15.76±1.58) years fulfilled the study criteria. The mean blood level and duration of VPA treatment were 65.81±22.18 mcg/ml and 98.57±135.94 days, respectively. The mean levels of thyroid-stimulating hormones and triglyceride levels increased significantly from the first to the last measurement. Platelet count decreased significantly following VPA treatment. No correlation was observed between these parameters and age, duration of treatment, or VPA levels. No serious adverse events were reported. Long-term VPA treatment in adolescents with psychiatric disorders is associated with significant increases in triglyceride levels. Moreover, VPA-treated adolescent psychiatric inpatients may be at risk of developing pituitary-thyroid axis dysregulation and decreased platelet count. Therefore, baseline measurement of thyroid functions and metabolic and hematological parameters and monitoring throughout the treatment are recommended.

Evaluation of thyroid hormones in children receiving carbamazepine or valproate: a prospective study

The aim of this study was to determine the alterations in thyroid function during carbamazepine or valproate monotherapy in a prospective study. Forty patients treated with valproate, 33 patients treated with carbamazepine, and 36 control patients, all aged between 2 and 18 years, were enrolled in our study. Serum levels of thyroid hormones were measured before the beginning of the antiepileptic therapy and at 6 and 12 months of treatment. Carbamazepine-treated patients showed mean serum thyroid hormone levels significantly lower than baseline evaluation and the control group. Thyroid-stimulating hormone levels at 6 and 12 months were not significantly different in carbamazepine treated patients. Serum hormone levels did not change during valproate treatment. Thyroid-stimulating hormone levels were significantly higher at the 12th month of valproate treatment. Our data suggest that although carbamazepine causes significant alterations in thyroid hormone levels, these changes do not lead to clinical symptoms at the follow-up period of 12 months.

Adverse drug reactions induced by valproic acid

Valproic acid is a widely-used first-generation antiepileptic drug, prescribed predominantly in epilepsy and psychiatric disorders. VPA has good efficacy and pharmacoeconomic profiles, as well as a relatively favorable safety profile. However, adverse drug reactions have been reported in relation with valproic acid use, either as monotherapy or polytherapy with other antiepileptic drugs or antipsychotic drugs. This systematic review discusses valproic acid adverse drug reactions, in terms of hepatotoxicity, mitochondrial toxicity, hyperammonemic encephalopathy, hypersensitivity syndrome reactions, neurological toxicity, metabolic and endocrine adverse events, and teratogenicity.