Cardiac sodium channel inhibition by lamotrigine: in vitro characterization and clinical implications

An overview of drug-induced sodium channel blockade and changes in cardiac conduction: Implications for drug safety

The human voltage-gated sodium channel Nav1.5 (hNav1.5/SCN5A) plays a critical role in the initiation and propagation of action potentials in cardiac myocytes, and its modulation by various drugs has significant implications for cardiac safety. Drug-dependent block of Nav1.5 current (INa) can lead to significant alterations in cardiac electrophysiology, potentially resulting in conduction slowing and an increased risk of proarrhythmic events. This review aims to provide a comprehensive overview of the mechanisms by which various pharmacological agents interact with Nav1.5, focusing on the molecular determinants of drug binding and the resultant electrophysiological effects. We discuss the structural features of Nav1.5 that influence drug affinity and specificity. Special attention is given to the concept of state-dependent block, where drug binding is influenced by the conformational state of the channel, and its relevance to therapeutic efficacy and safety. The review also examines the clinical implications of INa block, highlighting case studies of drugs that have been associated with adverse cardiac events, and how the Vaughan-Williams Classification system has been employed to qualify "unsafe" sodium channel block. Furthermore, we explore the methodologies currently used to assess INa block in nonclinical and clinical settings, with the hope of providing a weight of evidence approach including in silico modeling, in vitro electrophysiological assays and in vivo cardiac safety studies for mitigating proarrhythmic risk early in drug discovery. This review underscores the importance of understanding Nav1.5 pharmacology in the context of drug development and cardiac risk assessment.

Deconvoluting and derisking QRS complex widening to improve cardiac safety profile of novel plasmepsin X antimalarials

Quinoline-related antimalarial drugs have been associated with cardiotoxicity risk, in particular QT prolongation and QRS complex widening. In collaboration with Medicines for Malaria Venture, we discovered novel plasmepsin X (PMX) inhibitors for malaria treatment. The first lead compounds tested in anesthetized guinea pigs (GPs) induced profound QRS widening, although exhibiting weak inhibition of NaV1.5-mediated currents in standard patch clamp assays. To understand the mechanism(s) underlying QRS widening to identify further compounds devoid of such liability, we established a set of in vitro models including CaV1.2, NaV1.5 rate-dependence, and NaV1.8 patch clamp assays, human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM), and Langendorff-perfused isolated GP hearts. Six compounds were tested in all models including anesthetized GP, and 8 additional compounds were tested in vitro only. All compounds tested in anesthetized GP and isolated hearts showed a similar cardiovascular profile, consisting of QRS widening, bradycardia, negative inotropy, hypotension, and for some, QT prolongation. However, a left shift of the concentration-response curves was noted from in vitro to in vivo GP data. When comparing in vitro models, there was a good consistency between decrease in sodium spike amplitude in hiPSC-CM and QRS widening in isolated hearts. Patch clamp assay results showed that the QRS widening observed with PMX inhibitors is likely multifactorial, primarily due to NaV1.8 and NaV1.5 rate-dependent sodium blockade and/or calcium channel-mediated mechanisms. In conclusion, early de-risking of QRS widening using a set of different in vitro assays allowed to identify novel PMX inhibitors with improved cardiac safety profile.

Optimizing β-lactam-containing antibiotic combination therapy for the treatment of Buruli ulcer

AIMS

The current treatment for Buruli ulcer is based on empirical evidence of efficacy. However, there is an opportunity for shortening its duration and improving response rates. Evolving understanding of the pharmacokinetic-pharmacodynamic relationships provides the basis for a stronger dose rationale for antibiotics. In conjunction with modelling and simulation, it is possible to identify dosing regimens with the highest probability of target attainment (PTA). This investigation aims to: (i) assess the dose rationale for a new combination therapy including amoxicillin/clavulanic acid (AMX/CLV) currently in clinical trials; and (ii) compare its performance with alternative dosing regimens including rifampicin, clarithromycin and AMX/CLV.

METHODS

In vitro estimates of the minimum inhibitory (MIC) concentration were selected as a measure of the antibacterial activity of different drug combinations. Clinical trial simulations were used to characterize the concentration vs. time profiles of rifampicin, clarithromycin and amoxicillin in a virtual cohort of adult and paediatric patients, considering the effect of baseline covariates on disposition parameters and interindividual variability in exposure. The PTA of each regimen was then assessed using different thresholds of the time above MIC.

RESULTS

A weight-banded dosing regimen including 150-600 mg rifampicin once daily, 250-1000 mg clarithromycin and AMX/CLV 22.5 mg/kg /1000 mg twice daily ensures higher PTA than the standard of care with AMX/CLV 45 mg/kg/2000 mg once daily.

CONCLUSION

The higher PTA values support the proposed 4-drug combination (rifampicin, clarithromycin, AMX/CLV) currently under clinical investigation. Our findings also suggest that higher rifampicin doses might contribute to enhanced treatment efficacy.

The Roller Coaster of Lamotrigine Levels: Successful Treatment of Massive Lamotrigine Overdose With Continuous Veno-Venous Hemodiafiltration and Rifampin

Lamotrigine is a commonly used anticonvulsant in treating seizures and bipolar disorder, but there is very limited literature on the management of its toxicity. Case reports have been published suggesting the potential role of hemodialysis in lowering serum lamotrigine levels, as well as sodium bicarbonate and lipid emulsion in treating dysrhythmia. After previously reported therapies failed to stabilize the patient's condition, the case presents our successful treatment experience using continuous veno-venous hemodiafiltration (CVVHDF) to stabilize lamotrigine levels, as well as intravenous rifampin as adjunctive therapy to facilitate lamotrigine metabolism. This is a 66-year-old male who was found unresponsive after a lamotrigine overdose. His first lamotrigine level was 42.3 ug/mL. Hemodialysis was started on hospital day 1. Despite hemodialysis sessions, his lamotrigine level rebounded with worsening neurological and cardiac symptoms. On hospital day 3, he developed wide-QRS complex tachyarrhythmia and hemodynamic instability with a lamotrigine level of 66.9 ug/mL. Sodium bicarbonate was given without effect. Lipid emulsion was administered which terminated the arrhythmia. CVVHDF and rifampin were started and lamotrigine levels have continuously downtrended since. He was successfully extubated on day 7. Lamotrigine level became undetectable on day 9. The patient was discharged to a psychiatric facility without any neurological or mobility impairment on day 10. The continuous drug clearance provided by CVVHDF over intermittent hemodialysis may have provided additional benefit in lamotrigine level stabilization, while rifampin use in this case may have further accelerated lamotrigine metabolism. As the first case reporting CVVHDF and rifampin use, our experience suggests their potential roles in managing severe lamotrigine toxicity.

Lamotrigine use and potential for adverse cardiac effects: A retrospective evaluation in a Veteran population

OBJECTIVE

To identify the impact of lamotrigine (LTG) on cardiac rhythm and conduction abnormalities for Veterans, an especially vulnerable population.

BACKGROUND

In October 2020 the US Food and Drug Administration (FDA) added a new warning to the label of lamotrigine (Lamictal™) regarding its potential to cause cardiac rhythm and conduction abnormalities [1]. This warning came following in vitro data which suggested Class IB antiarrhythmic effects occurring at clinically achievable concentrations of lamotrigine [2]. However, it is unclear whether the in vitro findings will result in adverse clinical outcomes. Our objective was to assess for evidence for adverse clinical outcomes in a vulnerable population and examine for subtler signs of an association between lamotrigine and cardiac rhythm disturbances.

METHODS

A retrospective chart review was conducted using records between 10-01-2017 and 07-06-2021, identifying patients at the William S. Middleton Memorial Veterans Hospital who were prescribed lamotrigine. Data collected included: dates of lamotrigine initiation or discontinuation, lamotrigine dosing over the time of the prescription and maximum lamotrigine dose, any cardiac-related ICD-10-CM codes or a history of a cardiology appointment, EKGs with any abnormalities or changes, any concomitantly prescribed medications with known potential to cause cardiac abnormalities, any cardiac deaths. This retrospective chart review was approved by the University of Wisconsin-Madison Institutional Review Board.

RESULTS

Two hundred and thirty-three (189 male) patients with a lamotrigine prescription and 41.2 % (n = 96) of these patients had an EKG performed while prescribed lamotrigine. The average age of patients was 64.3 ± 13.0 (range 29 to 90) years and mean maximum lamotrigine daily dose was 250.8 ± 148.2 mg (range 25 to 800 mg). Nearly half (47.9 %, 46/96) of the patients were prescribed a concomitant sodium channel blocking medication in addition to lamotrigine. Eighty-four of the patients (87.5 %, 84/96) had a cardiac diagnosis, while 12 (12.5 %, 12/96) did not. A total of 12 deaths occurred within the review period, with two cardiac deaths from congestive heart failure. Four cases did not have information on cause of death. No LTG-associated cardiac adverse effects were noted as part of clinical care, though rash was noted in 5 cases. A total of 7 (7.3 %, 7/96) patients were found to have EKG abnormalities potentially related to lamotrigine, including 7.1 % (6/84) of those with a cardiac diagnosis and 8.3 % (1/12) of those without a cardiac diagnosis.

CONCLUSIONS

While recent FDA warnings have suggested caution regarding cardiac complications associated with lamotrigine based on in vitro studies, the clinical implications are uncertain. Despite selecting a particularly vulnerable population, this retrospective chart review did not identify any deaths due to cardiac rhythm or conduction causes, nor demonstrate unambiguous cardiac complications related to lamotrigine. Even using permissive criteria (including any prolonged PR or QTc) to examine for subtle effects, only a low incidence (<10 %) of potential complications was found. Broader implications of this study are limited by the number of patients included and the retrospective nature of the study. Therefore, further studies are warranted to evaluate a link between cardiac complications and the use of lamotrigine, including the role of concomitant medications such as other sodium channel blocking agents and psychotropic medications.

Mexiletine: Antiarrhythmic mechanisms, emerging clinical applications and mortality

Mexiletine, a class Ib antiarrhythmic drug, exhibits its major antiarrhythmic effect via inhibition of the fast and late Na+ currents in myocardial tissues that are dependent on the opening of Na+ channels for their excitation. Through a comprehensive examination of mexiletine's therapeutic benefits and potential risks, we aim to provide valuable insights that reinforce its role as a vital therapeutic option for patients with ventricular arrhythmias, long QT syndrome, and other heart rhythm disorders. This review will highlight the current understandings of the antiarrhythmic effects and rationales for recent off-label use and address the mortality and proarrhythmic effects of mexiletine utilizing published basic and clinical studies over the past five decades.

Investigation of cardiac arrhythmia events in patients treated with lamotrigine: FDA adverse event reporing system analysis

OBJECTIVES

In October 2020 and March 2021, the U.S. Food and Drug Administration (FDA) classified lamotrigine as a class IB antiarrhythmic, announcing an increased risk of heart rhythm problems. We sought to investigate the nature of the arrhythmia signal with lamotrigine use compared to anticonvulsants with sodium-blocking and non-sodium-blocking mechanisms.

METHODS

This retrospective pharmacovigilance case-non-case study used disproportionality analysis to detect signals of adverse reaction of interest reported with lamotrigine to the FDA Adverse Event Reporting System (FAERS) between 1998 and 2022. Our regression model adjusted for interacting concomitant medications. Sensitivity analyses included stratifying by indication and publication date.

RESULTS

Overall, 2917 cases of heart rhythm problems with anticonvulsants were analyzed (1557 female [58.4%] and 1109 male [41.6%]). The mean age ± standard deviation (SD) was 43 ± 19, the groups did not differ significantly by age. Forty cases (7.91%) in the epileptic indication included more than one concomitant medication that influences cardiac conduction. The disproportionality signal for cardiac arrest did not differ for lamotrigine compared with other anticonvulsants, adjusted reporting odds ratio (adj.ROR, .88; 95% CI, .59-1.29) in the epileptic indication. A significantly lower reporting risk for bradyarrhythmia was identified with lamotrigine users in the epileptic population, (adj.ROR, .45; 95% confidence interval [CI], .29-.68). The psychiatric indication demonstrated a sixfold reporting risk for cardiac arrest compared to the epileptic indication. Concomitant medications that affect cardiac conduction, as well as reports on overdose and suicide attempts, were significant variables in psychiatric patients (ROR, 2.45; 95% CI, 2.21-2.71) and (ROR, 1.44; 95% CI, 1.34-1.55), respectively.

SIGNIFICANCE

Our results do not support a significant difference in the reporting risk for cardiac arrest, syncope, tachyarrhythmia, and bradyarrhythmia with lamotrigine in the epileptic indication. Signals of cardiac arrest in lamotrigine could be explained by confounding factors in the psychiatric indication, such as greater concomitant use of medications with cardiac adverse events, and greater reports on overdose and suicide attempts. We recommend that patients with polypharmacy undergo clinical and electrocardiographic monitoring. We illustrate the importance of examining signals for separate indications.

"Appraisal of state-of-the-art" The 2021 Distinguished Service Award of the Safety Pharmacology Society: Reflecting on the past to tackle challenges ahead

This appraisal of state-of-the-art manuscript highlights and expands upon the thoughts conveyed in the lecture of Dr. Jean-Pierre Valentin, recipient of the 2021 Distinguished Service Award of the Safety Pharmacology Society, given on the 2nd December 2021. The article reflects on the strengths, weaknesses, opportunities, and threats that surrounded the evolution of safety and secondary pharmacology over the last 3 decades with a particular emphasis on pharmaceutical drug development delivery, scientific and technological innovation, complexities of regulatory framework and people leadership and development. The article further built on learnings from past experiences to tackle constantly emerging issues and evolving landscape whilst being cognizant of the challenges facing these disciplines in the broader drug development and societal context.

A novel approach for pharmacological substantiation of safety signals using plasma concentrations of medication and administrative/healthcare databases: a case study using Danish registries for an FDA warning on lamotrigine

PHARMACOM-EPI is a novel framework to predict plasma concentrations of drugs at the time of occurrence of clinical outcomes. In early 2021, the U.S. Food and Drug Administration (FDA) issued a warning on the antiseizure drug lamotrigine claiming that it has the potential to increase the risk of arrhythmias and related sudden cardiac death due to a pharmacological sodium channel-blocking effect. We hypothesized that the risk of arrhythmias and related death is due to toxicity. We used the PHARMACOM-EPI framework to investigate the relationship between lamotrigine's plasma concentrations and the risk of death in older patients using real-world data. Danish nationwide administrative and healthcare registers were used as data sources and individuals aged 65 years or older during the period 1996 - 2018 were included in the study. According to the PHARMACOM-EPI framework, plasma concentrations of lamotrigine were predicted at the time of death and patients were categorized into non-toxic and toxic groups based on the therapeutic range of lamotrigine (3-15mg/L). Over 1 year of treatment, the incidence rate ratio (IRR) of all-cause mortality was calculated between the propensities score matched toxic and non-toxic groups. In total, 7286 individuals were diagnosed with epilepsy and were exposed to lamotrigine, 432 of which had at least one plasma concentration measurement The pharmacometric model by Chavez et al. was used to predict lamotrigine's plasma concentrations considering the lowest absolute percentage error among identified models (14.25%, 95% CI: 11.68-16.23). The majority of lamotrigine associated deaths were cardiovascular-related and occurred among individuals with plasma concentrations in the toxic range. The IRR of mortality between the toxic group and non-toxic group was 3.37 [95% CI: 1.44-8.32] and the cumulative incidence of all-cause mortality exponentially increased in the toxic range. Application of our novel framework PHARMACOM-EPI provided strong evidence to support our hypothesis that the increased risk of all-cause and cardiovascular death was associated with a toxic plasma concentration level of lamotrigine among older lamotrigine users.

The Anti-Epileptic Drugs Lamotrigine and Valproic Acid Reduce the Cardiac Sodium Current

Anti-epileptic drugs (AEDs) are associated with increased risk of sudden cardiac death. To establish whether gabapentin, lamotrigine, levetiracetam, pregabalin, and valproic acid reduce the Na_v1.5 current, we conducted whole-cell patch-clamp studies to study the effects of the five AEDs on currents of human cardiac Na_v1.5 channels stably expressed in HEK293 cells, and on action potential (AP) properties of freshly isolated rabbit ventricular cardiomyocytes. Lamotrigine and valproic acid exhibited inhibitory effects on the Na_v1.5 current in a concentration-dependent manner with an IC₅₀ of 142 ± 36 and 2022 ± 25 µM for lamotrigine and valproic acid, respectively. In addition, these drugs caused a hyperpolarizing shift of steady-state inactivation and a delay in recovery from inactivation. The changes on the Na_v1.5 properties were reflected by a reduction in AP upstroke velocity (43.0 ± 6.8% (lamotrigine) and 23.7 ± 10.6% (valproic acid) at 1 Hz) and AP amplitude; in contrast, AP duration was not changed. Gabapentin, levetiracetam, and pregabalin had no effect on the Na_v1.5 current. Lamotrigine and valproic acid reduce the Na_v1.5 current density and affect its gating properties, resulting in a decrease of the AP upstroke velocity. Gabapentin, levetiracetam, and pregabalin have no effects on the Na_v1.5 current.

Unmasking of Brugada syndrome by lamotrigine in a patient with pre-existing epilepsy: A case report with review of the literature

Brugada syndrome is an inherited cardiac channelopathy arising from mutations in voltage-gated cardiac sodium channels. Idiopathic epilepsy portrays a coalescent underlying pathophysiological mechanism pertaining to the premature excitation of neuronal voltage-gated ion channels resulting in the disruption of presynaptic neurons and the unregulated release of excitatory neurotransmitters. The coexistence of epilepsy and Brugada syndrome may be explained by mutations in voltage-gated ion channels, which are coexpressed in cardiac and neural tissue. Moreover, the incidence of sudden unexpected death in epilepsy has been associated with malignant cardiac arrhythmias in the presence of mutations in voltage-gated ion channels. Lamotrigine is an antiepileptic drug that inhibits neuronal voltage-gated sodium channels, thus stabilizing neural impulse propagation and controlling seizure activity in the brain. However, lamotrigine has been shown to inhibit cardiac voltage-gated sodium channels resulting in a potential arrhythmogenic effect and the ability to unmask Brugada syndrome in genetically susceptible individuals. We are reporting a case of a 27-year-old male patient with a background of presumed idiopathic epilepsy who was initiated on lamotrigine therapy resulting in the unmasking of Brugada syndrome and the onset of syncopal episodes. This case provides further evidence for the arrhythmogenic capacity of lamotrigine and highlights the relationship between epilepsy and Brugada syndrome. In this report, we aim to review the current literature regarding the associations between epilepsy and Brugada syndrome and the impact of lamotrigine therapy on such patients.