Ezogabine: An Evaluation of Its Efficacy and Safety as Adjunctive Therapy for Partial-Onset Seizures in Adults

Pharmacokinetics of XEN496, a Novel Pediatric Formulation of Ezogabine, Under Fed and Fasted Conditions: A Phase 1 Trial

INTRODUCTION

XEN496 is a novel, granular, immediate-release formulation of ezogabine intended for pediatric use. The objective of this study was to assess the effect of food on the pharmacokinetics (PK) of XEN496 and its N-acetyl metabolite (NAMR) in healthy volunteers.

METHODS

Twenty-four adult subjects were enrolled in this phase 1, single center, open-label, randomized, single-dose, two-way crossover study. Subjects received 400 mg XEN496 as an oral suspension in both fed and fasted states separated by a 6-day washout period. Serial blood samples were collected up to 48 h post-administration. PK parameters evaluated included maximum observed plasma concentration (C_max), time of maximum observed plasma concentration (T_max), and area under the concentration-time curve (AUC_(0-t) and AUC_inf). Safety was assessed by laboratory evaluations, physical exam, and adverse event monitoring.

RESULTS

For XEN496, median T_max was 3 and 2 h in the fed and fasted states, respectively. AUC parameters in the fed and fasted states were equivalent, whereas food decreased C_max of XEN496 by 32% compared to the fasted state. The ratio of geometric means [90% CI] for C_max was 72% [64-82%]. For NAMR, food delayed T_max by 1 h, while C_max and AUC parameters were equivalent in the fed and fasted states. The safety profile of XEN496 in this study appeared comparable to that previously reported for ezogabine tablets.

CONCLUSION

The biopharmaceutical performance of XEN496 in this study was as expected for an immediate-release, granular dosage formulation, and generally comparable to that reported for ezogabine tablets. Future studies are needed to characterize the efficacy, safety, and PK of XEN496 in a pediatric population.

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.

The Modulation of Potassium Channels in the Smooth Muscle as a Therapeutic Strategy for Disorders of the Gastrointestinal Tract

Alterations of smooth muscle contractility contribute to the pathophysiology of important functional gastrointestinal disorders (FGIDs) such as functional dyspepsia and irritable bowel syndrome. Consequently, drugs that decrease smooth muscle contractility are effective treatments for these diseases. Smooth muscle contraction is mainly triggered by Ca(2+) influx through voltage-dependent channels located in the plasma membrane. Thus, the modulation of the membrane potential results in the regulation of Ca(2+) influx and cytosolic levels. K(+) channels play fundamental roles in these processes. The open probability of K(+) channels increases in response to various stimuli, including membrane depolarization (voltage-gated K(+) [K(V)] channels) and the increase in cytosolic Ca(2+) levels (Ca(2+)-dependent K(+) [K(Ca)] channels). K(+) channel activation is mostly associated with outward K(+) currents that hyperpolarize the membrane and reduce cell excitability and contractility. In addition, some K(+) channels are open at the resting membrane potential values of the smooth muscle cells in some gut segments and contribute to set the resting membrane potential itself. The closure of these channels induces membrane depolarization and smooth muscle contraction. K(V)1.2, 1.5, 2.2, 4.3, 7.4 and 11.1, K(Ca)1.1 and 2.3, and inwardly rectifying type 6K(+) (K(ir)6) channels play the most important functional roles in the gastrointestinal smooth muscle. Activators of all these channels may theoretically relax the gastrointestinal smooth muscle and could therefore be promising new therapeutic options for FGID. The challenge of future drug research and development in this area will be to synthesize molecules selective for the channel assemblies expressed in the gastrointestinal smooth muscle.

Advances in anti-epileptic drug testing

In the past twenty-one years, 17 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are clobazam, ezogabine (retigabine), eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. Therapeutic drug monitoring is often used in the clinical dosing of the newer anti-epileptic drugs. The drugs with the best justifications for drug monitoring are lamotrigine, levetiracetam, oxcarbazepine, stiripentol, and zonisamide. Perampanel, stiripentol and tiagabine are strongly bound to serum proteins and are candidates for monitoring of the free drug fractions. Alternative specimens for therapeutic drug monitoring are saliva and dried blood spots. Therapeutic drug monitoring of the new antiepileptic drugs is discussed here for managing patients with epilepsy.

Activation of peripheral KCNQ channels attenuates inflammatory pain

Background

Refractory chronic pain dramatically reduces the quality of life of patients. Existing drugs cannot fully achieve effective chronic pain control because of their lower efficacy and/or accompanying side effects. Voltage-gated potassium channels (KCNQ) openers have demonstrated their analgesic effect in preclinical and clinical studies, and are thus considered to be a potential therapeutic target as analgesics. However, these drugs exhibit a narrow therapeutic window due to their imposed central nerve system (CNS) side effects. To clarify the analgesic effect by peripheral KCNQ channel activation, we investigated whether the analgesic effect of the KCNQ channel opener, retigabine, is inhibited by intracerebroventricular (i.c.v.) administration of the KCNQ channel blocker, 10, 10-bis (4-Pyridinylmethyl)-9(10H) -anthracenone dihydrochloride (XE-991) in rats.

Results

Oral administration (p.o.) of retigabine showed an anticonvulsant effect on maximal electronic seizures and an analgesic effect on complete Freund’s adjuvant-induced thermal hyperalgesia. However, impaired motor coordination and reduced exploratory behavior were also observed at the analgesic doses of retigabine. Administration (i.c.v.) of XE-991 reversed the retigabine-induced anticonvulsant effect, impaired motor coordination and reduced exploratory behavior but not the analgesic effect. Moreover, intraplantar administration of retigabine or an additional KCNQ channel opener, N-(6-Chloro-pyridin-3-yl)-3,4-difluoro-benzamide (ICA-27243), inhibited formalin-induced nociceptive behavior.

Conclusions

Our findings suggest that the peripheral sensory neuron is the main target for KCNQ channel openers to induce analgesia. Therefore, peripheral KCNQ channel openers that do not penetrate the CNS may be suitable analgesic drugs as they would prevent CNS side effects.

Phosphatidylinositol 4,5-bisphosphate alters pharmacological selectivity for epilepsy-causing KCNQ potassium channels

Pharmacological augmentation of neuronal KCNQ muscarinic (M) currents by drugs such as retigabine (RTG) represents a first-in-class therapeutic to treat certain hyperexcitatory diseases by dampening neuronal firing. Whereas all five potassium channel subtypes (KCNQ1-KCNQ5) are found in the nervous system, KCNQ2 and KCNQ3 are the primary players that mediate M currents. We investigated the plasticity of subtype selectivity by two M current effective drugs, retigabine and zinc pyrithione (ZnPy). Retigabine is more effective on KCNQ3 than KCNQ2, whereas ZnPy is more effective on KCNQ2 with no detectable effect on KCNQ3. In neurons, activation of muscarinic receptor signaling desensitizes effects by retigabine but not ZnPy. Importantly, reduction of phosphatidylinositol 4,5-bisphosphate (PIP2) causes KCNQ3 to become sensitive to ZnPy but lose sensitivity to retigabine. The dynamic shift of pharmacological selectivity caused by PIP2 may be induced orthogonally by voltage-sensitive phosphatase, or conversely, abolished by mutating a PIP2 site within the S4-S5 linker of KCNQ3. Therefore, whereas drug-channel binding is a prerequisite, the drug selectivity on M current is dynamic and may be regulated by receptor signaling pathways via PIP2.