The efficacy and safety of retigabine and other adjunctive treatments for refractory partial epilepsy: A systematic review and indirect comparison

Efficacy, tolerability and safety of add-on third-generation antiseizure medications in treating focal seizures worldwide: a network meta-analysis of randomised, placebo-controlled trials

Background

Adjunctive newer antiseizure medications (ASMs) are being used in patients with treatment-resistant focal-onset seizures (FOS). An updated network meta-analysis (NMA) was necessary to compile evidence in this critical area.

Methods

We systematically searched PubMed, Embase, Cochrane Library, Web of Science, and Scopus from their inception until 17 January 2024, evaluating the efficacy, tolerability, and safety of rufinamide (RUF), brivaracetam (BRV), cenobamate (CNB), eslicarbazepine (ESL), lacosamide (LCM), retigabine (RTG), and perampanel (PER) as adjunctive treatments for FOS. Efficacy outcomes included seizure response and seizure freedom. Tolerability was assessed by discontinuation due to adverse events (AEs). Safety outcomes were evaluated based on the number of patients experiencing at least one AE and serious adverse events (SAEs). This review is registered with PROSPERO (CRD42023485130).

Findings

A total of 29 studies involving 11,750 participants were included. For seizure response, all ASMs were significantly superior to placebo, with RTG ranking highest, followed by CNB. Considering dosage, CNB 400 mg/d was top-ranked, followed by RTG 1200 mg/d. For seizure freedom, BRV was highest-ranked, followed by CNB, with BRV 100 mg/d leading, followed by CNB 400 mg/d. Regarding tolerability, LCM 600 mg/d had the lowest ranking, followed by CNB 400 mg/d. For the safety outcome of AEs, ESL 1200 mg/d was ranked lowest, followed by CNB 400 mg/d. Regarding SAEs, LCM 400 mg/d was ranked lowest, followed by RTG 1200 mg/d.

Interpretation

ASMs at different dosages have varying efficacy and tolerability profiles. We have provided hierarchical rankings of ASMs for efficacy and safety outcomes. Our findings offer the most comprehensive evidence available to inform patients, families, physicians, guideline developers, and policymakers about the choice of ASMs in patients with treatment-resistant FOS.

Funding

None.

Recent Progress in the Development of New Antiepileptic Drugs with Novel Targets

Background

Epilepsy is a chronic neurological disorder that affects approximately 50-70 million people worldwide. Epilepsy has a significant economic and social burden on patients as well as on the country. The recurrent, spontaneous seizure activity caused by abnormal neuronal firing in the brain is a hallmark of epilepsy. The current antiepileptic drugs provide symptomatic relief by restoring the balance of excitatory and inhibitory neurotransmitters. Besides, about 30% of epileptic patients do not achieve seizure control. The prevalence of adverse drug reactions, including aggression, agitation, irritability, and associated comorbidities, is also prevalent. Therefore, researchers should focus on developing more effective, safe, and disease-modifying agents based on new molecular targets and signaling cascades.

Summary

This review overviews several clinical trials that help identify promising new targets like lactate dehydrogenase inhibitors, c-jun n-terminal kinases, high mobility group box-1 antibodies, astrocyte reactivity inhibitors, cholesterol 24-hydroxylase inhibitors, glycogen synthase kinase-3 beta inhibitors, and glycolytic inhibitors to develop a new antiepileptic drug.

Key messages

Approximately 30% of epileptic patients do not achieve seizure control. The current anti-seizure drugs are not disease modifying, cure or prevent epilepsy. Lactate dehydrogenase inhibitor, cholesterol 24-hydroxylase inhibitor, glycogen synthase kinase-3 beta inhibitors, and mTOR inhibitors have a promising antiepileptogenic effect.

Modifications of the Triaminoaryl Metabophore of Flupirtine and Retigabine Aimed at Avoiding Quinone Diimine Formation

The potassium channel opening drugs flupirtine and retigabine have been withdrawn from the market due to occasional drug-induced liver injury (DILI) and tissue discoloration, respectively. While the mechanism underlying DILI after prolonged flupirtine use is not entirely understood, evidence indicates that both drugs are metabolized in an initial step to reactive ortho- and/or para-azaquinone diimines or ortho- and/or para-quinone diimines, respectively. Aiming to develop safer alternatives for the treatment of pain and epilepsy, we have attempted to separate activity from toxicity by employing a drug design strategy of avoiding the detrimental oxidation of the central aromatic ring by shifting oxidation toward the formation of benign metabolites. In the present investigation, an alternative retrometabolic design strategy was followed. The nitrogen atom, which could be involved in the formation of both ortho- or para-quinone diimines of the lead structures, was shifted away from the central ring, yielding a substitution pattern with nitrogen substituents in the meta position only. Evaluation of K_V7.2/3 opening activity of the 11 new specially designed derivatives revealed surprisingly steep structure-activity relationship data with inactive compounds and an activity cliff that led to the identification of an apparent "magic methyl" effect in the case of N-(4-fluorobenzyl)-6-[(4-fluorobenzyl)amino]-2-methoxy-4-methylnicotinamide. This flupirtine analogue showed potent K_V7.2/3 opening activity, being six times as active as flupirtine itself, and by design is devoid of the potential for azaquinone diimine formation.

Understanding the challenge of comparative effectiveness research in focal epilepsy: A review of network meta-analyses and real-world evidence on antiepileptic drugs

OBJECTIVE

Head-to-head randomized controlled trials (RCTs) are the gold standard for assessing comparative treatment effects. In the absence of direct comparisons between all possible antiepileptic drugs (AEDs), however, clinical decision-making in focal (partial onset) epilepsy relies on alternative evidence borne from indirect comparisons including network meta-analyses (NMAs) and from real-world evidence (RWE) studies. We review NMAs and observational RWE studies comparing AEDs in the adjunctive setting to compare the robustness of these methods and to formulate recommendations for future evidence development.

METHODS

A literature review identified NMAs and RWE studies comparing AEDs for the adjunctive treatment of focal seizures published between January 2008 and October 2018. NMAs were evaluated for robustness using a framework based on guidelines from the National Institute for Health and Care Excellence Decision Support Unit and the International Society for Pharmacoeconomics and Outcomes Research. RWE studies were evaluated using the GRACE checklist.

RESULTS

From a total of 1993 records, 11 NMAs and six RWE studies were eligible. Key limitations identified in the NMAs include nonsystematic selection of RCTs, unexplored heterogeneity between included RCTs in terms of study and patient characteristics, and selection of AEDs and AED doses or dosing strategies that are not reflective of clinical practice. The main limitations of RWE studies concern sample size, design, and analysis methods. Approximately 90% of comparisons between individual AEDs were nonsignificant in the NMAs. None of the RWE studies adjusted for baseline differences between comparator groups; therefore, they lack the validity to make comparative conclusions.

SIGNIFICANCE

Current NMAs and RWE studies provide only nominal comparative evidence for AED treatments in focal epilepsy, and should be used with caution for decision-making due to their methodological limitations. To overcome these hurdles, adherence to methodological guidelines and concerted efforts to collect relevant outcome data in the real world are needed.

Relative performance of brivaracetam as adjunctive treatment of focal seizures in adults: a network meta-analysis

Objective: To estimate the relative efficacy, safety and tolerability of adjunctive brivaracetam and other antiepileptic drugs (AEDs) using a Bayesian network meta-analysis (NMA) approach. Methods: A systematic literature review (SLR) identified randomized controlled trials of AEDs treating focal (partial-onset) seizures for ≥8 weeks and assessed them for inclusion in the NMA. Bayesian random-effects NMA was performed for several outcomes. All interventions within the licensed dose range were included in the network of evidence. Results: The SLR identified 82 studies; 65 were included in the NMA. These studies had baseline mean age 33.1-38.0 years, mean duration of epilepsy 18.7-23.0 years and median seizure frequency/28 days 8.1-11.8. All AEDs had significantly higher odds than placebo of achieving ≥50% responder rates (odds ratios 1.83-3.58) and all AEDs had a trend of higher odds than placebo of achieving seizure freedom (odds ratios 1.36-5.73), most being statistically significant. Tolerability outcomes were comparable between AEDs; most AEDs had higher odds than placebo of treatment-emergent adverse events leading to discontinuation, serious AEs, nausea, fatigue, dizziness and somnolence. Conclusions: This NMA would appear to show relative equivalence in efficacy, safety and tolerability outcomes of the included AEDs. However, patient heterogeneity within trials and in clinical practice should be considered when interpreting these results. While NMAs are based on the best available evidence the authors suggest that, due to the inability of NMAs to capture unmeasured confounding factors and population heterogeneity, NMAs must not be the sole basis for comparative treatment recommendations.

Efficacy of antiepileptic drugs in the adjunctive treatment of refractory partial-onset seizures: Meta-analysis of pivotal trials

OBJECTIVE

In the absence of randomized clinical trials (RCTs) assessing the relative efficacy of antiepileptic drugs (AEDs), meta-analyses are useful resources for informing treatment choices. This meta-analysis assesses the relative efficacy and tolerability of AEDs for adjunctive treatment of refractory partial onset seizures (POS).

METHODS

A systematic literature review was conducted to identify pivotal AED trials serving as the basis for US Food and Drug Administration (FDA) approval.

INCLUSION CRITERIA

1) double-blind, placebo-controlled, parallel-group design, with 8- to 14-week maintenance period; 2) enrolled patients ≥16years with refractory POS, including complex partial seizures; 3) study was conducted between 1993 and 2013; and; 4) patients received FDA-approved dosage. Outcomes analyzed: 1) 50% responder rate (≥50% reduction from baseline in seizure frequency); 2) seizure freedom (proportion of seizure-free patients); and 3) discontinuation due to adverse events (AEs). DerSimonian and Laird random-effects model was used to derive odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

A total of 29 publications for 11 AEDs (eslicarbazepine, ezogabine, gabapentin, lacosamide, levetiracetam, perampanel, pregabalin, tiagabine, topiramate, vigabatrin, and zonisamide) were included in the meta-analysis. Tiagabine 56mg/day (OR 8.82, 95% CI: 2.77-28.11), pregabalin 600mg/day (OR 8.08, 95% CI: 5.45-11.98), and vigabatrin 3000mg/day (OR 6.23, 95% CI: 1.46-26.20) had the highest OR versus placebo of 50% response. The odds of seizure freedom were ≥7 times greater than placebo for levetiracetam 3000mg/day (OR 11.00, 95% CI: 2.08-58.06), vigabatrin 3000mg/day (OR 7.41, 95% CI: 1.31-41.84), and ezogabine 1200mg/day (OR 7.09, 95% CI: 0.36-58.06). Patients were more likely to discontinue any AED (except low-dose pregabalin) than placebo.

CONCLUSION

In this meta-analysis of >9000 patients, those treated with AEDs were more likely than placebo to achieve seizure response or freedom. Patients receiving pregabalin, tiagabine, and vigabatrin had the highest odds of ≥50% reduction in seizures, and patients receiving ezogabine, levetiracetam, and vigabatrin had the highest odds of seizure freedom.

Pore- and voltage sensor-targeted KCNQ openers have distinct state-dependent actions

Ion channels encoded by KCNQ2-5 generate a prominent K⁺ conductance in the central nervous system, referred to as the M current, which is controlled by membrane voltage and PIP2. The KCNQ2-5 voltage-gated potassium channels are targeted by a variety of activating compounds that cause negative shifts in the voltage dependence of activation. The underlying pharmacology of these effects is of growing interest because of possible clinical applications. Recent studies have revealed multiple binding sites and mechanisms of action of KCNQ activators. For example, retigabine targets the pore domain, but several compounds have been shown to influence the voltage-sensing domain. An important unexplored feature of these compounds is the influence of channel gating on drug binding or effects. In the present study, we compare the state-dependent actions of retigabine and ICA-069673 (ICA73, a voltage sensor-targeted activator). We assess drug binding to preopen states by applying drugs to homomeric KCNQ2 channels at different holding voltages, demonstrating little or no association of ICA73 with resting states. Using rapid solution switching, we also demonstrate that the rate of onset of ICA73 correlates with the voltage dependence of channel activation. Retigabine actions differ significantly, with prominent drug effects seen at very negative holding voltages and distinct voltage dependences of drug binding versus channel activation. Using similar approaches, we investigate the mechanistic basis for attenuation of ICA73 actions by the voltage-sensing domain mutation KCNQ2[A181P]. Our findings demonstrate different state-dependent actions of pore- versus voltage sensor-targeted KCNQ channel activators, which highlight that subtypes of this drug class operate with distinct mechanisms.

Efficacy and safety of antiepileptic drugs for refractory partial-onset epilepsy: a network meta-analysis

The optimal combination of antiepileptic drugs (AEDs) for the treatment of refractory partial-onset epilepsy is a perpetual point of debate. While several network meta-analyses (NMAs) have been published, conclusions remain controversial, especially since newer AEDs have been introduced. In our review, we included the newer AEDs to evaluate the comparative efficacy and safety of AEDs for the treatment of refractory partial-onset epilepsy. We searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials (Cochrane Library 2017, Issue 1) from their inception to February 18, 2017. The risk of bias in the included randomized controlled trials (RCTs) was evaluated according to the Cochrane Collaboration's risk of bias tool. An NMA was performed with a Bayesian random-effects model, and we used the surface under the cumulative ranking curve to detect the optimal AEDs. Seventy-six RCTs with 17 AEDs and 20,711 patients were included in the NMAs, which showed that Brivaracetam (BRV), Levetiracetam (LEV), Oxcarbazepine (OXC), Topiramate, Vigabatrin (VGB), and Valproate (VPA) had a greater likelihood of allowing patients to achieve seizure freedom. We also found that LEV was associated with a lower withdrawal rate due to adverse effects than Lacosamide, Eslicarbazepine acetate, OXC, Pregabalin, and Retigabine. LEV, VGB, VPA, and BRV emerged as the agents with the best combination of properties when considering the efficacy and safety outcomes based on the full double-blind treatment period. However, it is critical to perform RCTs and to obtain prospective data from representative cohort studies.

Real life pharmaceutical treatment patterns for adult patients with focal epilepsy in Germany: a longitudinal and cross-sectional analysis of recently approved anti-epileptic drugs

Objectives: The aim of this study was to investigate the antiepileptic drug (AED) treatment of adults suffering from focal epilepsies (FE) in Germany. Of special interest was the number and percentage of the patients 16 years and older receiving no treatment with an AED, treatment with one AED (monotherapy), treatment with more than one AED, and treatment with a novel AED. The definition for “novel” was newly approved at the time of market entry since 2006 (last 10 years): eslicarbazepine (ESL), lacosamide (LCM), perampanel (PER), and retigabine (RTG).

Methods: The analysis was based on a claims data set covering the years 2007 to 2014, provided by AOK PLUS, a German statutory health insurance. Two patient samples were defined: (1) prevalent patients suffering from FE (at least one in- or outpatient diagnosis of FE and at least one prescription of an AED), and (2) incident FE patients (first in- or outpatient diagnosis of FE without any previous diagnoses/AED prescriptions in the preceding 6 months). Patient observation started at date of first observed inpatient or outpatient focal epilepsy diagnosis within the analyzed period.

Each patient was classified as a “no AED therapy”, “AED monotherapy” or “more than one AED therapy”. Patients were analyzed by number and type of concomitantly prescribed AEDs in yearly tranches (no, one, two, three, four, more than four AEDs; novel versus non-novel AEDs).

Results: A total of 34,422 patients diagnosed with FE aged 16 year or older (mean age 59.6 years, 48.7% female) were identified. The mean follow-up period was 1,891 days (5.2 years) since first confirmed diagnosis.

The percentage of prevalent patients diagnosed with FE who received one AED (monotherapy) was stable overall and ranged between a minimum of 66.2% (2007) and a maximum of 68.9% (2010). The percentage of patients who received two AEDs ranged from 23.6% (2012) to 25.8% (2007). The remaining patients received therapies with three (6.0% in 2010 to 6.7% in 2007), four (1.0% in 2010 to 1.2% in 2009) or more than four AEDs (0.1% in 2014 to 0.3% in 2013). Between 8.1%–16.6% (2007; 2014) of the patients received no AED therapy in the observed period.

In the first year after the diagnosis of FE (incident patients), 9.7% of patients didn’t receive any AED therapy. Of those treated with at least one AED, 80.0% received one AED (monotherapy) only, 17.0% received therapy with two AEDs, 2.6% with three AEDs, 0.3% with four AEDs, and 0.1% with >4 AEDs during the respective observation time window and remained stable throughout the four-year follow-up period.

Of prevalent patients with a diagnosis of FE, 1,889 (5.5%) received at least one prescription of a novel AED during the observation period; 98.6% of these patients received the novel AED in combination with at least one other AED. Of those patients, 269 (14.2%) received >1 novel AED. The analysis of the patients receiving novel AEDs by the time from the first confirmed diagnosis of FE until the prescription of a novel AED resulted in a mean duration of 4.0 years (SD 2.0) for ESL, 3.6 years (SD 2.2) for LCM, 5.7 years (SD 1.2) for PER, and 4.6 years (SD 0.8 years) for RTG. The mean number of AEDs prescribed before the novel AEDs were 3.2 for ESL, 2.4 for LCM, 5.0 for PER and 5.2 for RTG.

Conclusions: Most patients aged 16 years or older, suffering from focal seizures, received AED monotherapy. Novel AEDs were prescribed in a small proportion of patients (<6%) and relatively late in the treatment course. These results are consistent with the recommendations of the German Society for Epileptology (Deutsche Gesellschaft für Epileptologie, DGfE) which suggests a number of monotherapy options – these options do not include the novel AEDs described in this study.

Efficacy and tolerability of brivaracetam compared to lacosamide, eslicarbazepine acetate, and perampanel as adjunctive treatments in uncontrolled focal epilepsy: Results of an indirect comparison meta-analysis of RCTs

BACKGROUND

Brivaracetam (BRV), eslicarbazepine acetate (ESL), lacosamide (LCM), and perampanel (PER) have been recently marketed as adjunctive treatments for focal onset seizures. To date, no randomized controlled trial (RCT) has directly compared BRV with ESL, LCM, or PER.

PURPOSE

To compare BRV with the other add-on AEDs in patients with uncontrolled focal epilepsy, estimating their efficacy and tolerability through an adjusted, common-reference based indirect comparison meta-analysis.

METHODS

We systematically searched RCTs in which add-on treatment with ESL or LCM in patients with focal onset seizures have been compared with placebo. Efficacy and tolerability outcomes were considered. Random-effects Mantel-Haenszel meta-analyses were performed to obtain odds ratios (ORs) for the efficacy of BRV, LCM, ESL, or PER versus placebo. Adjusted indirect comparisons were then made between BRV and the other three AEDs using the obtained results, comparing the minimum and the highest effective recommended daily dose of each drug.

RESULTS

Seventeen RCTs, with a total of 4971 patients were included. After adjusting for dose-effects, indirect comparisons showed no difference between BRV and LCM, ESL, or PER for responder rate and seizure freedom. Lower adverse events were observed with high dose BRV compared to high dose ESL or PER, but no difference was found in withdrawing because of adverse events.

CONCLUSIONS

Indirect comparisons do not demonstrate a significant difference in efficacy between add-on BRV and LCM, ESL, or PER in focal epilepsy, and might suggest a better tolerability of BRV than ESL, and possibly also PER, at the highest effective recommended dose.

Sequence determinants of subtype-specific actions of KCNQ channel openers

KEY POINTS

Retigabine is a KCNQ voltage-gated potassium channel opener that was recently approved as an add-on therapeutic for patients with drug-resistant epilepsy. Retigabine exhibits very little specificity between most KCNQ channel subtypes, and there is interest in generating more potent and specific KCNQ channel openers. The present study describes the marked specificity of ICA069673 for KCNQ2 vs. KCNQ3, and exploits this property to investigate determinants of KCNQ subtype specificity. ICA069673 acts on a binding site in the voltage-sensing domain that is distinct from the putative retigabine site in the channel pore. ICA069673 has two separable effects on KCNQ channel activity. We identify two channel residues required for subtype specificity of KCNQ channel openers and show that these are sufficient to generate ICA069673 sensitivity in KCNQ3.

ABSTRACT

Retigabine (RTG) is the first approved anti-epileptic drug that acts via activation of voltage-gated potassium channels, targeting KCNQ channels that underlie the neuronal M-current. RTG exhibits little specificity between KCNQ2-5 as a result of conservation of a Trp residue in the pore domain that binds to the drug. The RTG analogue ICA-069673 ('ICA73') exhibits much stronger effects on KCNQ2 channels, including a large hyperpolarizing shift of the voltage-dependence of activation, an ∼2-fold enhancement of peak current and pronounced subtype specificity for KCNQ2 over KCNQ3. Based on ICA73 sensitivity of chimeric constructs of the transmembrane segments of KCNQ2 and KCNQ3, this drug appears to interact with the KCNQ2 voltage sensor (S1-S4) rather than the pore region targeted by RTG. KCNQ2 point mutants in the voltage sensor were generated based on KCNQ2/KCNQ3 sequence differences, and screened for ICA73 sensitivity. These experiments reveal that KCNQ2 residues F168 and A181 in the S3 segment are essential determinants of ICA73 subtype specificity. Mutations at either position in KCNQ2 abolish the ICA73-mediated gating shift, but preserve RTG sensitivity. Interestingly, A181P mutant channels show little ICA73-mediated gating shift but retain current potentiation by the drug. Mutations (L198F and P211A), which introduce these critical KCNQ2 residues at corresponding positions in KCNQ3, transplant partial ICA73 sensitivity. These findings demonstrate that RTG and ICA73 act via distinct mechanisms, and also reveal specific residues that underlie subtype specificity of KCNQ channel openers.

Two-year real-world experience with perampanel in patients with refractory focal epilepsy: Austrian data

BACKGROUND

The aim of this study was to analyse registry data of seizure outcome and adverse events (AEs) for perampanel as add-on therapy in patients with focal epilepsy since its approval in 2012 for adjunctive treatment of focal epilepsy in patients ⩾12 years.

METHOD

A retrospective 2-year chart review of all patients receiving perampanel was carried out.

RESULTS

A total of 122 patients received perampanel [median treatment length: 20.1 (range: 3.4-26.8) months]; 71 (58%) remained on treatment at last follow up. Overall, 33 patients (27%) were seizure-free for ⩾3 months at last follow up; of these, eight were seizure free for ⩾3 times the longest interictal interval before perampanel therapy; 18 (15%) had reduced seizure frequency ⩾50%. A total of 58 (47%) had an AE and 34 (28%) withdrew from treatment because of AEs. AEs included dizziness (33%), fatigue (12%), psychiatric symptoms (8%), cognitive deficits (7%), speech problems (5%), nausea (4%) and gait problems (4%). AEs subsided in 17/18 patients (94%) following a 2 mg dose reduction. A total of 43 (35%) took a concomitant enzyme inducer. Patients not taking enzyme inducers were more likely to be seizure free (p = 0.002); there were no other between-group differences.

CONCLUSIONS

Perampanel was well tolerated and improved seizure control in 42% of patients (50- 100% reduction), with higher rates in those not receiving a concomitant enzyme inducer. AEs, particularly dizziness, were common but often disappeared with a slight dose reduction. The results are consistent with those from randomized controlled trials.

[Impact of early benefit assessment on patients with epilepsy in Germany: Current healthcare provision and therapeutic needs]

Epilepsy is one of the most common chronic neurological diseases and represents a significant burden for patients, their families and society. In more than 75 % of patients anticonvulsant therapy consists of valproate, carbamazepine, lamotrigine or levetiracetam. There is a need for polytherapy in drug-refractory patients and they suffer from negative effects on quality of life and employment that is associated with high indirect costs. To allow a comprehensive treatment in this patient group, access to new anticonvulsants with novel modes of action is needed; however, all applications for new antiepileptic drugs failed to prove added benefits during the Pharmaceutical Market Restructuring Act (AMNOG) in Germany. One of the main reasons is the mandatory definition of a standard comparative therapy. It remains unclear whether there will be studies in the future which will fulfill the requirements of the current version of AMNOG. Observational studies after approval and marketing of new antiepileptic drugs could be better alternatives to prove added benefits for individual patients in the current German healthcare system.

Atomic basis for therapeutic activation of neuronal potassium channels

Retigabine is a recently approved anticonvulsant that acts by potentiating neuronal M-current generated by KCNQ2–5 channels, interacting with a conserved Trp residue in the channel pore domain. Using unnatural amino-acid mutagenesis, we subtly altered the properties of this Trp to reveal specific chemical interactions required for retigabine action. Introduction of a non-natural isosteric H-bond-deficient Trp analogue abolishes channel potentiation, indicating that retigabine effects rely strongly on formation of a H-bond with the conserved pore Trp. Supporting this model, substitution with fluorinated Trp analogues, with increased H-bonding propensity, strengthens retigabine potency. In addition, potency of numerous retigabine analogues correlates with the negative electrostatic surface potential of a carbonyl/carbamate oxygen atom present in most KCNQ activators. These findings functionally pinpoint an atomic-scale interaction essential for effects of retigabine and provide stringent constraints that may guide rational improvement of the emerging drug class of KCNQ channel activators.

The antiepileptic drug retigabine potentiates neuronal KCNQ potassium channels. Here, the authors use a combination of unnatural amino acid mutagenesis and electrophysiology to show that retigabine acts by hydrogen bonding with a tryptophan indole nitrogen in the channel pore.

Discovery of a novel Kv7 channel opener as a treatment for epilepsy

Facilitating activation, or delaying inactivation, of the native Kv7 channel reduces neuronal excitability, which may be beneficial in controlling spontaneous electrical activity during epileptic seizures. In an effort to identify a compound with such properties, the structure-activity relationship (SAR) and in vitro ADME for a series of heterocyclic Kv7.2-7.5 channel openers was explored. PF-05020182 (2) demonstrated suitable properties for further testing in vivo where it dose-dependently decreased the number of animals exhibiting full tonic extension convulsions in response to corneal stimulation in the maximal electroshock (MES) assay. In addition, PF-05020182 (2) significantly inhibited convulsions in the MES assay at doses tested, consistent with in vitro activity measure. The physiochemical properties, in vitro and in vivo activities of PF-05020182 (2) support further development as an adjunctive treatment of refractory epilepsy.

Cardiovascular responses to retigabine in conscious rats--under normotensive and hypertensive conditions

BACKGROUND AND PURPOSE

Retigabine is a recently approved antiepileptic agent which activates Kv7.2-7.5 potassium channels. It is emerging that these channels have an important role in vascular regulation, but the vascular effects of retigabine in the conscious state are unknown. Hence, in the present study we assessed the regional haemodynamic responses to retigabine in conscious rats.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were chronically instrumented with pulsed Doppler flow probes to measure regional haemodynamic responses to retigabine under control conditions and during acute hypertension induced by infusion of angiotensin II and arginine vasopressin. Further experiments were performed, using the β-adrenoceptor antagonists CGP 20712A, ICI 118551 and propranolol, to elucidate the roles of β-adrenoceptors in the responses to retigabine in vivo and in vitro.

KEY RESULTS

Under normotensive conditions, retigabine induced dose-dependent hypotension and hindquarters vasodilatation, with small, transient renal and mesenteric vasodilatations. In the acutely hypertensive state, the renal and mesenteric, but not hindquarters, vasodilatations were enhanced. The response of the hindquarters vascular bed to retigabine was mediated, in part, by β₂-adrenoceptors. However, in vitro experiments confirmed that retigabine did not act as a β-adrenoceptor agonist.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that retigabine causes regionally specific vasodilatations, which are different under normotensive and hypertensive conditions, and are, in part, mediated by β₂-adrenoceptors in some vascular beds but not in others. These results broadly support previous findings and further indicate that Kv7 channels are a potential therapeutic target for the treatment of vascular diseases associated with inappropriate vasoconstriction.

Network meta-analyses of antiepileptic drug efficacy and tolerability in drug-resistant focal epilepsies: a clinical perspective

PURPOSE

Network meta-analysis (NMA) is a new technique that allows multiple treatment comparisons and provides estimates of effect sizes for all possible pair-wise comparisons. Several NMAs of antiepileptic drug (AED) efficacy and tolerability in individuals with refractory focal epilepsy, however, came to non-specific and, in some cases, divergent conclusions. We review some clinical factors that may be responsible for these inconsistent findings.

RESULTS

A major issue is the small number of individuals included in the meta-analyses with consequent wide confidence intervals and lack of ability to achieve significant results. Further issues are lack of robustness of the measured efficacy outcome-the responder ratio (the percentage of individuals with a >50 % improvement in seizure frequency); the selection of randomized studies (RCTs) included, i.e., the inclusion of studies with heterogeneous populations (children and adults); and inclusion of people treated with different doses of the experimental drug. Some methods of analysing data from RCTs, such as the last observation carried forward (LOCF) analysis, the choice of different phases of the study to compare to baseline, and the year in which the trial was conducted, selectively affect measurement of efficacy outcomes. Titration speed and other methodological aspects selectively affect tolerability.

CONCLUSION

Several factors restrict the analysis of clinically useful estimates of the comparative efficacy of AEDs, while analysis of tolerability may be easier to accomplish.

The efficacy and tolerability of perampanel and other recently approved anti-epileptic drugs for the treatment of refractory partial onset seizure: a systematic review and Bayesian network meta-analysis

OBJECTIVES

This paper compares the efficacy and tolerability of perampanel (PER) relative to other recently approved anti-epileptic drug (AEDs) - lacosamide (LCS), retigabine (RTG), and eslicarbazepine (ESL) for the adjunctive treatment of partial onset seizures with or without secondary generalization and specifically in the secondary generalization subgroup.

MATERIALS AND METHODS

A systematic literature review of all RCTs of PER and selected AEDs in EMBASE, Medline, and the Cochrane Central from 1998 to January 2011 with an update in PubMed in March 2013 was performed. A network meta-analysis was conducted for 50% responder rate for overall seizures; withdrawal due to adverse events; seizure freedom; and 50% responder rate for secondary generalized seizures.

RESULTS

Twelve RCTs (three PER, three LCS, three RTG and three ESL) were included. PER performed significantly better than placebo for 'responder rate' (OR 2.151, 95% CrI 1.348-3.472) and 'seizure freedom' (OR 2.507, 95% CrI 1.067-7.429). When compared to other agents, PER was found to be equally effective. For 'withdrawal due to adverse events', PER had the lowest odds ratio vs. placebo compared with other AEDs. In the analysis for the subgroup of patients with secondary generalization, only four RCTs (three PER and one LCS) met the inclusion criteria for one outcome (responder rate) for LCS. In this subgroup, PER was statistically significantly better than placebo (OR 2.448, 95% CrI 1.088-5.828).

CONCLUSION

PER was statistically significantly superior to placebo in responder rate, seizure freedom, and responder rate in the secondary generalization population. Though PER had statistically significant greater withdrawal compared to placebo, it had the lowest ORs vs. placebo, suggesting a superior safety profile among the comparators included in this analysis. In patients with partial onset seizure with secondary generalization, PER had a statistically significant effect on responder rate compared to placebo.

Retigabine as add-on treatment of refractory epilepsy--a cost-utility study in a Swedish setting

OBJECTIVES

To calculate comparative incremental cost-effectiveness ratios (cost per quality-adjusted life year, QALY) and net marginal benefits for retigabine as add-on treatment for patients with uncontrolled focal seizures as compared to add-on lacosamide treatment and no add-on treatment, respectively.

MATERIALS & METHODS

Calculations were performed using a validated decision-tree model. The study population consisted of adult patients with focal-onset epilepsy in published randomized placebo-controlled add-on trials of retigabine or lacosamide. Healthcare utilization and QALY for each treatment alternative were calculated. Probabilistic sensitivity analysis was performed using the specification of this model as a basis for Monte Carlo simulations. 2009 prices were used for all costs.

RESULTS

Results were reported for a 2-year follow-up period. Retigabine add-on treatment was both more effective and less costly than lacosamide add-on treatment, and the cost per additional QALY for the retigabine no add-on (standard) therapy comparison was estimated at 2009€ 15,753. Using a willingness-to-pay threshold for a QALY of € 50,000, the net marginal values were estimated at 2009€ 605,874 for retigabine vs lacosamide and 2009€ 2,114,203 for retigabine vs no add-on, per 1,000 patients. The probabilistic analyses showed that the likelihood that retigabine treatment is cost-effective is at least 70%.

CONCLUSIONS

The estimated cost per additional QALY, for the retigabine vs no add-on treatment comparison, is well within the range of newly published estimates of willingness to pay for an additional QALY. Thus, add-on retigabine treatment for people with focal-onset epilepsy with no/limited response to standard antiepileptic treatment appears to be cost-effective.

Neurological adverse events of new generation sodium blocker antiepileptic drugs. Meta-analysis of randomized, double-blinded studies with eslicarbazepine acetate, lacosamide and oxcarbazepine

PURPOSE

Analysis of overall tolerability and neurological adverse effects (AEs) of eslicarbazepine acetate (ESL), lacosamide (LCM) and oxcarbazepine (OXC) from double-blind, placebo-controlled trials. Indirect comparisons of patients withdrawing because of AEs, and the incidence of some vestibulocerebellar AEs between these three antiepileptic dugs (AEDs).

METHODS

We searched MEDLINE for all randomized, double-blind, placebo-controlled trials investigating therapeutic effects of fixed oral doses of ESL, LCM and OXC in patients with drug resistant epilepsy. Withdrawal rate due to AEs, percentages of patients with serious AEs, and the proportion of patients experiencing any neurological AE, nausea and vomiting were assessed for their association with the experimental drug. Analyses were performed between recommended daily doses of each AED according to the approved summary of product characteristics (SPC). Risk differences were used to evaluate the association of any AE [99% confidence intervals (CIs)] or study withdrawals because of AEs (95% CIs) with the experimental drug. Indirect comparisons between withdrawal rate and AEs dizziness, coordination abnormal/ataxia and diplopia were estimated according to network meta-analysis (Net-MA).

RESULTS

Eight randomized, placebo-controlled, double-blind trials (4 with ESL, 3 with LCM, and 1 with OXC) were included in our analysis. At high doses (OXC 1200mg, ESL 1200mg and LCM 400mg) there was an increased risk of AE-related study withdrawals compared to placebo for all drugs. Several AEs were associated with the experimental drug. Both number and frequency of AEs were dose-related. At high recommended doses, patients treated with OXC withdrew from the experimental treatment significantly more frequently than patients treated with ESL and LCM. Furthermore, the AEs coordination abnormal/ataxia and diplopia were significantly more frequently observed in patients treated with OXC compared to patients treated with LCM and ESL.

CONCLUSIONS

The overall tolerability of AEDs and the incidence of several neurological AEs were clearly dose-dependent. Indirect comparisons between these AEDs, taking into account dose-effect, showed that OXC may be associated with more frequent neurological AEs than LCM and ESL.

Systematic review and meta-analysis of the efficacy and safety of perampanel in the treatment of partial-onset epilepsy

INTRODUCTION

Perampanel is a first-in-class antiepileptic drug approved for adjunctive treatment of partial-onset seizure in patients aged 12 years or older. Published randomised controlled trials (RCTs) had small sample sizes, and meta-analyses have included too few studies to draw conclusive results for the assessment of tolerability, efficacy and safety of perampanel. There is a need to conduct a meta-analysis with a larger dataset and an appropriate study design.

OBJECTIVE

The aim of this study was to systematically review the efficacy and safety of perampanel in the treatment of partial-onset epilepsy.

METHODS

Electronic and clinical trials databases were searched for RCTs of perampanel published up to March 2013. Outcomes of interest were 50 % responder rates, seizure freedom, treatment-emergent adverse events (TEAEs) and incidence of withdrawal. Meta-analysis was performed to investigate the outcomes of interest.

RESULTS

Five RCTs with a total of 1,678 subjects were included. The 50 % responder rates were significantly greater in patients receiving 4, 8 and 12 mg perampanel versus placebo, with risk ratios of 1.54 (95 % CI 1.11-2.13), 1.80 (95 % CI 1.38-2.35) and 1.72 (95 % CI 1.17-2.52), respectively. There was no statistical evidence of a difference in seizure freedom between 8 or 12 mg perampanel and placebo. Of the five commonly reported TEAEs included, both dizziness and somnolence were statistically associated with 8 mg perampanel, whilst dizziness was statistically associated with 12 mg perampanel. Incidences of withdrawal due to adverse events were significantly higher in the 8 mg and 12 mg perampanel groups versus placebo.

CONCLUSION

The use of perampanel resulted in a statistically significant reduction of seizure frequency with respect to the 50 % responder rate in patients with partial-onset epilepsy. Perampanel is well tolerated at 4 mg and reasonably tolerated at 8 and 12 mg. Further clinical and pharmacovigilance studies are required to investigate the long-term efficacy and safety of perampanel in the management of other types of epilepsy.