Retrospective evaluation of tiagabine overdose

Insight into the Structure of the Neutral Amino Acid Transporter B0AT2 Enabled the Discovery of Tiagabine as an Inhibitor

The sodium-dependent membrane transporter SLC6A15 (B0AT2) belongs to the SLC6 family, which comprises carriers of amino acids and monoamines. B0AT2 is expressed in the central nervous system (CNS), including the glutaminergic and GABAergic system. SLC6A15 supplies neurons with neutral amino acids. Its main substrates, branched-chain amino acids, and proline serve for glutamate biosynthesis, whereas silencing of B0AT2 leads to lower levels of neuronal glutamate. Recent research revealed that polymorphisms in the vicinity of slc6a15 are associated with major depressive disorder and anxiety. Mouse B0AT2 knockouts, by contrast, showed an antianxiety feature. Applying computational tools, we constructed models of B0AT2. Their structure was discussed extensively, enabling insight into the determinants of transport mechanism and substrate selectivity. Understanding the molecular basis of the B0AT2 inhibition by loratadine led to the discovery of a new inhibitor that is tiagabine, an anticonvulsant drug prescribed off-label in the treatment of anxiety and possessing antidepressant features. The results showed that tiagabine appears to have a higher affinity to the transporter than loratadine, which is the most potent inhibitor to date. Our findings support the development of new B0AT2 inhibitors that could be useful for investigating their therapeutic relevance, while the identification of tiagabine as a novel SLC6A15 inhibitor adds a new dimension to the pharmacological complexity of this drug.

Antiepileptic Drug Tiagabine Does Not Directly Target Key Cardiac Ion Channels Kv11.1, Nav1.5 and Cav1.2

Tiagabine is an antiepileptic drug used for the treatment of partial seizures in humans. Recently, this drug has been found useful in several non-epileptic conditions, including anxiety, chronic pain and sleep disorders. Since tachycardia-an impairment of cardiac rhythm due to cardiac ion channel dysfunction-is one of the most commonly reported non-neurological adverse effects of this drug, in the present paper we have undertaken pharmacological and numerical studies to assess a potential cardiovascular risk associated with the use of tiagabine. A chemical interaction of tiagabine with a model of human voltage-gated ion channels (VGICs) is described using the molecular docking method. The obtained in silico results imply that the adverse effects reported so far in the clinical cardiological of tiagabine could not be directly attributed to its interactions with VGICs. This is also confirmed by the results from the isolated organ studies (i.e., calcium entry blocking properties test) and in vivo (electrocardiogram study) assays of the present research. It was found that tachycardia and other tiagabine-induced cardiac complications are not due to a direct effect of this drug on ventricular depolarization and repolarization.

Non-health care facility anticonvulsant medication errors in the United States

INTRODUCTION

This study provides an epidemiological description of non-health care facility medication errors involving anticonvulsant drugs.

METHODS

A retrospective analysis of National Poison Data System data was conducted on non-health care facility medication errors involving anticonvulsant drugs reported to US Poison Control Centers from 2000 through 2012.

RESULTS

During the study period, 108,446 non-health care facility medication errors involving anticonvulsant pharmaceuticals were reported to US Poison Control Centers, averaging 8342 exposures annually. The annual frequency and rate of errors increased significantly over the study period, by 96.6 and 76.7%, respectively. The rate of exposures resulting in health care facility use increased by 83.3% and the rate of exposures resulting in serious medical outcomes increased by 62.3%. In 2012, newer anticonvulsants, including felbamate, gabapentin, lamotrigine, levetiracetam, other anticonvulsants (excluding barbiturates), other types of gamma aminobutyric acid, oxcarbazepine, topiramate, and zonisamide, accounted for 67.1% of all exposures.

CONCLUSIONS

The rate of non-health care facility anticonvulsant medication errors reported to Poison Control Centers increased during 2000-2012, resulting in more frequent health care facility use and serious medical outcomes. Newer anticonvulsants, although often considered safer and more easily tolerated, were responsible for much of this trend and should still be administered with caution.

The Influence of Solid Microneedles on the Transdermal Delivery of Selected Antiepileptic Drugs

The aim of this project was to examine the effect of microneedle rollers on the percutaneous penetration of tiagabine hydrochloride and carbamazepine across porcine skin in vitro. Liquid chromatography-mass spectrometric analysis was carried out using an Agilent 1200 Series HPLC system coupled to an Agilent G1969A TOF-MS system. Transdermal flux values of the drugs were determined from the steady-state portion of the cumulative amount versus time curves. Following twelve hours of microneedle roller application, there was a 6.74-fold increase in the percutaneous penetration of tiagabine hydrochloride (86.42 ± 25.66 µg/cm²/h) compared to passive delivery (12.83 ± 6.30 µg/cm²/h). For carbamazepine in 20% ethanol, passive transdermal flux of 7.85 ± 0.60 µg/cm²/h was observed compared to 10.85 ± 0.11 µg/cm²/h after microneedle treatment. Carbamazepine reconstituted in 30% ethanol resulted in only a 1.19-fold increase in drug permeation across porcine skin (36.73 ± 1.83 µg/cm²/h versus 30.74 ± 1.32 µg/cm²/h). Differences in flux values of untreated and microneedle-treated porcine skin using solid microneedles for the transdermal delivery of tiagabine were statistically significant. Although there were 1.38- and 1.19-fold increases in transdermal flux values of carbamazepine when applied as 20% and 30% ethanol solutions across microneedle-treated porcine skin, respectively, the increases were not statistically significant.

Review of toxicity and trends in the use of tiagabine as reported to US poison centers from 2000 to 2012

BACKGROUND

Tiagabine is a novel antiepileptic that acts by increasing synaptic and extracellular gamma-aminobutyric acid concentrations. Information concerning overdose of tiagabine is limited. After introduction, an increasing number of off-label uses suggested that tiagabine use would increase. However in 2005 and 2008, warnings from the Food and Drug Administration (FDA) were issued on the risk of seizures in non-epileptic and increased suicide ideation. We evaluated the temporal trends associated with these two warnings as well as clinical outcomes from tiagabine overdose.

METHOD

A retrospective review of all single substance tiagabine exposures in National Poison Data System (NPDS) from 2000 to 2012.

RESULTS

A total of 2147 patients had ingested tiagabine, with a mean of 165 year(-1). This was disproportionally distributed, with a steep rise leading up to 2004 (max 559 year(-1)) and then a significant decline (p < 0.05) between 2005 and 2006. The number of cases reported to NPDS mirrored the sales of tiagabine. Clinical effects were predominantly neurological, with the most commonly reported effects being drowsiness (27%), agitation (19%), confusion (12%), seizures (11%), and tachycardia (10%). In all, 758 patients (35%) showed a major or moderate medical outcome, with no deaths reported. A disproportionate share of the major outcomes was in the suicide attempt group (73%). The majority of patients (75%) were treated in a health-care facility (HCF).

CONCLUSIONS

The HCF usage is likely due to high rate of symptomatic patients (59%) and the large proportion of suicide attempt cases. The frequency of tiagabine cases in NPDS mirrored pharmaceutical sales, with steep declines temporally related to the 2005 FDA warning.

Tiagabine in clinical practice: effects on seizure control and behavior

OBJECTIVE

Preapproval randomized controlled trials of antiepileptic drugs provide data in limited patient groups. We assessed the side effect and seizure reduction profile of tiagabine (TGB) in typical clinical practice.

METHODS

Investigators recorded adverse effect (AE), seizure, and assessment-of-benefit data prospectively in sequential patients treated open label with TGB.

RESULTS

Two hundred ninety-two patients (39 children) were enrolled to be treated long term with TGB. Seizure types were focal-onset (86%), generalized-onset (12%), both focal- and generalized-onset (0.3%), and multiple associated with Lennox-Gastaut Syndrome (2%). Two hundred thirty-one received at least one dose of TGB (median = 28 mg/day) and had follow-up seizure or AE data reported. Common AEs were fatigue, dizziness, psychomotor slowing, ataxia, gastrointestinal upset, weight change, insomnia, and "others" (mostly behavioral). Serious AEs occurred in 19 patients: behavioral effects (n = 12), status epilepticus (n = 3), others (n = 3), and sudden unexplained death (n = 1). No patients experienced suicidal ideation/behavior, rash, nephrolithiasis, or organ failure. Seizure outcomes were seizure freedom (5%), ≥75% reduction (12%), ≥50% reduction (23%), and increased number of seizures (17%), or new seizure type (1%).

CONCLUSIONS

Behavioral AEs occurred in a larger proportion of patients compared to those reported in TGB preapproval randomized controlled trials. A moderate percentage of patients had a meaningful reduction in seizure frequency. In clinical practice, TGB remains a useful antiepileptic drug.

Antiepileptic drugs: the old and the new

During the past decade several new antiepileptic drugs (AEDs) have become available, including new formulations of some of the older medications. Understanding the pharmacokinetics of the new AEDs is important because they are primarily used for adjunctive therapy and interactions with other medications can result in significant toxicities. The new-generation AEDs do not cause serious morbidity in overdose, and treatment is primarily supportive. Specific medications should be chosen based on the patient's history and presentation.

Increase in tiagabine serum concentration with coadministration of gemfibrozil

OBJECTIVE

To report a case of possible acute tiagabine toxicity secondary to administration of gemfibrozil.

CASE SUMMARY

A 39-year-old male was taking tiagabine 16 mg orally 3 times per day and carbamazepine 500 mg orally twice per day for complex partial seizures secondary to mesial temporal sclerosis. He was found to have type IV hypertriglyceridemia and was prescribed gemfibrozil. Because he reported severe confusion and altered consciousness shortly after a single 600-mg dose of gemfibrozil, he was admitted for controlled challenge with that drug. A single 300-mg dose of gemfibrozil resulted in lightheadedness and led to a 59% and 75% increase in total tiagabine serum concentrations at 2 and 5 hours, respectively, without significant change in baseline carbamazepine concentrations.

DISCUSSION

This is the first report of an interaction between the widely used antihyperlipidemic drug gemfibrozil and tiagabine. Since tiagabine, which was originally developed as an antiepileptic medication, is now being used widely for a variety of other indications such as anxiety and depression, there is an increased risk for clinically significant interactions with gemfibrozil.

CONCLUSIONS

Increased total and unbound tiagabine concentrations following a single 300-mg dose of gemfibrozil and reproduction of clinical symptoms with gemfibrozil rechallenge suggests the toxicity our patient experienced was due to a pharmacokinetic drug interaction. Use of the Horn Drug Interaction Probability Scale showed a probable interaction between gemfibrozil and tiagabine.

Tiagabine: efficacy and safety in partial seizures - current status

Tiagabine hydrochloride (TGB) is a selective gamma-aminobutyric acid (GABA) reuptake inhibitor. TGB is effective as an add-on medication in adults and children 12 years and older in the treatment of partial seizures. Results of nonrandomized add-on trials with TGB show treatment success with seizure reduction of at least 50% in 33% to 46% of patients. In newly diagnosed patients with partial epilepsy, TGB monotherapy was as effective as carbamazepine. Comedication with TGB elevates the risk of nonconvulsive status (7.8% vs 2.7% without TGB). The most common side effects include dizziness/lightheadedness, asthenia/lack of energy and somnolence. TGB has no negative effects on cognition; it does not increase the risk of fractures or rash. TGB may interfere with color perception. TGB presents an intermediate risk for depression in patients with epilepsy (approximately 4%). Regarding the risk of overdose, 96-680 mg TGB (mean 224 mg) caused seizures or coma. TGB is an antiepileptic drug exhibiting a specific anticonvulsive mechanism of action, the efficacy of which is relatively low when used in comedication. Critical side effects, such as the induction of nonconvulsive status epilepticus, further limit its use.