Pharmacokinetic interaction study between eslicarbazepine acetate and topiramate in healthy subjects

The Pharmacology and Toxicology of Third-Generation Anticonvulsant Drugs

Epilepsy is a neurologic disorder affecting approximately 50 million people worldwide, or about 0.7% of the population [1]. Thus, the use of anticonvulsant drugs in the treatment of epilepsy is common and widespread. There are three generations of anticonvulsant drugs, categorized by the year in which they were developed and released. The aim of this review is to discuss the pharmacokinetics, drug-drug interactions, and adverse events of the third generation of anticonvulsant drugs. Where available, overdose data will be included. The pharmacokinetic properties of third-generation anticonvulsant drugs include relatively fewer drug-drug interactions, as well as several unique and life-threatening adverse events. Overdose data are limited, so thorough review of adverse events and knowledge of drug mechanism will guide expectant management of future overdose cases. Reporting of these cases as they occur will be necessary to further clarify toxicity of these drugs.

Update on the role of eslicarbazepine acetate in the treatment of partial-onset epilepsy

Eslicarbazepine acetate (ESL) is a once daily new third generation antiepileptic drug that shares the basic chemical structure of carbamazepine and oxcarbazepine - a dibenzazepine nucleus with the 5-carboxamide substituent, but is structurally different at the 10,11-position. ESL is a pro-drug metabolized to its major active metabolite eslicarbazepine. Despite the fact that the exact mechanism of action has not been fully elucidated, it is thought to involve inhibition of voltage-gated sodium channels (VGSC). ESL inhibits sodium currents in a voltage-dependent way by an interaction predominantly with the inactivated state of the VGSC, thus selectively reducing the activity of rapidly firing (epileptic) neurons. ESL reduces VGSC availability through enhancement of slow inactivation. In Phase III studies, adjunctive therapy with ESL 800 or 1,200 mg/day leads to a significant decrease in the seizure frequency in adults with refractory partial onset epilepsy. Based on these results, ESL has been approved in Europe (by the European Medicines Agency) and in the United States (by the US Food and Drug Administration) as add-on therapy. Data on efficacy and safety have been confirmed by 1-year extension and real life observational studies. Recently, based on results from two randomized, double-blind, historical control Phase III trials, ESL received US Food and Drug Administration approval also as a monotherapy for patients with partial onset epilepsy. In the pediatric setting, encouraging results have been obtained suggesting its potential role in the management of epileptic children. Overall ESL was generally well tolerated. The most common adverse events were dizziness, somnolence, headache, nausea, diplopia, and vomiting. Adverse events can be minimized by appropriate titration. In conclusion, ESL seems to overcome some drawbacks of the previous antiepileptic drugs, suggesting a major role of ESL in the management of focal onset epilepsy for both new onset and refractory cases, either as monotherapy or as adjunctive treatment.

Eslicarbazepine acetate: a review of its use as adjunctive therapy in refractory partial-onset seizures

Eslicarbazepine acetate (Aptiom(®), Zebinix(®)) is approved for the adjunctive treatment of partial-onset seizures in adults aged ≥18 years. Adjunctive therapy with oral eslicarbazepine acetate 800 or 1,200 mg once daily was associated with a significantly lower standardized seizure frequency (primary endpoint) than placebo in patients aged ≥18 years with refractory partial-onset seizures in three, randomized, double-blind, multinational, phase III trials. In a fourth randomized, double-blind, multinational, phase III trial in patients aged ≥16 years with refractory partial-onset seizures, adjunctive eslicarbazepine acetate 1,200 mg once daily, but not 800 mg once daily, was associated with a significantly lower standardized seizure frequency (primary endpoint). Responder rates were significantly higher with eslicarbazepine acetate 1,200 mg once daily than with placebo in these four trials, and with eslicarbazepine acetate 800 mg once daily than with placebo in two trials. The efficacy of eslicarbazepine acetate was maintained in the longer term, according to the results of 1-year extension studies. Adjunctive therapy with oral eslicarbazepine acetate was generally well tolerated in patients with refractory partial-onset seizures, with most adverse events being of mild to moderate severity. In conclusion, eslicarbazepine acetate is a useful option for the adjunctive treatment of patients with refractory partial-onset seizures.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate

INTRODUCTION

The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults.

AREAS COVERED

For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper.

EXPERT OPINION

Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

Pharmacokinetics, drug interactions and exposure-response relationship of eslicarbazepine acetate in adult patients with partial-onset seizures: population pharmacokinetic and pharmacokinetic/pharmacodynamic analyses

BACKGROUND

Eslicarbazepine acetate (Zebenix®) is a voltage-gated sodium channel blocker approved in 2009 by the European Medicines Agency as adjunctive therapy in adults with partial-onset seizures, with or without secondary generalization.

OBJECTIVES

The objectives of the current population pharmacokinetic (PK) and PK/pharmacodynamic analyses were to characterize the population PK of eslicarbazepine (the main active metabolite of eslicarbazepine acetate), to evaluate the influence of patient factors and concomitant antiepileptic drugs (AEDs) on the PK variability of eslicarbazepine, to assess the effect of eslicarbazepine acetate on the PK of concomitant AEDs and to investigate the relationship between eslicarbazepine systemic exposure and eslicarbazepine acetate antiepileptic activity in patients with partial-onset seizures uncontrolled with one to three AEDs.

METHODS

Sparse plasma concentrations of eslicarbazepine and concomitant AEDs, along with efficacy data, were obtained from 641 patients enrolled in eslicarbazepine acetate phase III studies. Data were analysed using nonlinear mixed-effect modelling methods. Most analyses used a model using log-transformed data from trough concentration (minimum steady-state plasma concentration during a dosage interval [C(min,ss)]). The model estimated the apparent total body clearance from plasma (CL/F), which is sufficient to predict average plasma concentrations at steady state (C(av,ss)). After the final model was validated, individual concentrations at steady state were predicted, and exposure parameters (area under the plasma concentration-time curve over 24 hours, C(min,ss) and C(av,ss)) for a one-compartmental model with first-order elimination were calculated.

RESULTS

Eslicarbazepine CL/F was affected by bodyweight, dose of carbamazepine (D(CAR)) and co-administration of barbiturates or phenytoin (AED(PB)), as predicted by the equation CL/F = (2.36 + 0.00149 • D(CAR) + 1.41 • AED(PB)) • (weight/70)0.75, which means that CL/F is 2.36 L/h for a subject with a bodyweight of 70 kg and without concomitant carbamazepine and barbiturates/phenytoin. Concomitant use of lamotrigine, valproic acid, topiramate, gabapentin, clobazam and levetiracetam showed no effect on the exposure to eslicarbazepine. Inter-individual variability of eslicarbazepine CL/F was 44% and the residual error (intra-subject variability) was proportional to the log of concentrations, with a coefficient of variation of 6%. Age, ethnicity, sex and creatinine clearance did not affect eslicarbazepine CL/F. Eslicarbazepine acetate did not affect the CL/F of clobazam, gabapentin, phenytoin, phenobarbital, levetiracetam and valproic acid. Eslicarbazepine acetate slightly increased the CL/F of carbamazepine (up to 14%), lamotrigine (up to 12%) and topiramate (up to 16%). The antiepileptic effect of eslicarbazepine acetate, as assessed by a decrease in seizure frequency, increased with the increase of eslicarbazepine acetate dose and eslicarbazepine concentrations. The concomitant administration of other AEDs did not affect the eslicarbazepine acetate exposure-response relationship.

CONCLUSIONS

The magnitude of the effect of eslicarbazepine acetate on the CL/F of the concomitant AEDs assessed appears to be not clinically relevant and does not justify the need for dose adjustment in most patients. A continuous dose-response relationship was observed between eslicarbazepine concentrations and seizure frequency reduction, which was not affected by concomitant AEDs.

A review of eslicarbazepine acetate for the adjunctive treatment of partial-onset epilepsy

Eslicarbazepine acetate (ESL) is a novel antiepileptic drug indicated for the treatment of partial-onset seizures. Structurally, it belongs to the dibenzazepine family and is closely related to carbamazepine and oxcarbazepine. Its main mechanism of action is by blocking the voltage-gated sodium channel. ESL is a pro-drug that is rapidly metabolized almost exclusively into S-licarbazepine, the biologically active drug. It has a favorable pharmacokinetic and drug-drug interaction profile. However, it may induce the metabolism of oral contraceptives and should be used with caution in females of child-bearing age. In the pre-marketing placebo-controlled clinical trials ESL has proven effective as adjunctive therapy in adult patients with refractory of partial-onset seizures. Best results were observed on a single daily dose between 800 and 1200 mg. In general, ESL was well tolerated, with most common dose-related side effects including dizziness, somnolence, headache, nausea and vomiting. Hyponatremia has been observed (0.6%–1.3%), but the incidence appears to be lower than with the use of oxcarbazepine. There is very limited information on the use of ESL in children or as monotherapy.

Hepatic UDP-glucuronosyltransferase is responsible for eslicarbazepine glucuronidation

Eslicarbazepine acetate (ESL) is a once-daily novel antiepileptic drug approved in Europe for use as adjunctive therapy for refractory partial-onset seizures with or without secondary generalization. Metabolism of ESL consists primarily of hydrolysis to eslicarbazepine, which is then subject to glucuronidation followed by renal excretion. In this study, we have identified that human liver microsomes (HLM) enriched with uridine 5'-diphosphoglucuronic acid give origin to a single Escherichia coli β-glucuronidase-sensitive eslicarbazepine glucuronide (most likely the O-glucuronide). The kinetics of eslicarbazepine glucuronidation in HLM was investigated in the presence and absence of bovine serum albumin (BSA). The apparent K(m) were 412.2 ± 63.8 and 349.7 ± 74.3 μM in the presence and absence of BSA, respectively. Incubations with recombinant human UDP glucuronosyltransferases (UGTs) indicated that UGT1A4, UGT1A9, UGT2B4, UGT2B7, and UGT2B17 appear to be involved in eslicarbazepine conjugation. The UGT with the highest affinity for conjugation was UGT2B4 (K(m) = 157.0 ± 31.2 and 28.7 ± 10.1 μM, in the absence and presence of BSA, respectively). There was a significant correlation between eslicarbazepine glucuronidation and trifluoperazine glucuronidation, a typical UGT1A4 substrate; however, no correlation was found with typical substrates for UGT1A1 and UGT1A9. Diclofenac inhibited eslicarbazepine glucuronidation in HLM with an IC(50) value of 17 μM. In conclusion, glucuronidation of eslicarbazepine results from the contribution of UGT1A4, UGT1A9, UGT2B4, UGT2B7, and UGT2B17, but the high-affinity component of the UGT2B4 isozyme may play a major role at therapeutic plasma concentrations of unbound eslicarbazepine.

Pharmacotherapy of epilepsy: newly approved and developmental agents

This article discusses seven newly available antiepileptic drugs (AEDs) and agents in phase III development. Lacosamide, licensed as an adjunctive treatment for partial-onset seizures, primarily acts by enhancing sodium channel slow inactivation. At daily doses of 200-600 mg, the drug significantly reduced partial-onset seizures in adults with refractory epilepsy. The most common adverse effects are CNS related. Rufinamide, available as adjunctive treatment for seizures associated with Lennox-Gastaut syndrome, has an unclear mechanism of action, although it does block voltage-dependent sodium channels. Coadministration of valproic acid significantly increases rufinamide circulating concentrations. The drug has been shown to have efficacy for partial-onset, primary generalized tonic-clonic, tonic-atonic, absence and atypical absence seizures. Adverse effects are mainly somnolence, nausea and vomiting. Eslicarbazepine acetate, a carbamazepine analogue, was recently licensed as adjunctive treatment for partial-onset seizures. Eslicarbazepine acetate acts at voltage-gated sodium channels, although the precise mechanism of action is unclear. The drug had efficacy for partial-onset seizures in three randomized, double-blind, placebo-controlled studies, using 400, 800 or 1200 mg/day. Adverse effects include dizziness and somnolence. Retigabine (ezogabine) exerts its anticonvulsant effect through the opening of neuronal voltage-gated potassium channels. Following significant seizure reduction rates at dosages of 600, 900 and 1200 mg/day, license applications have been submitted for its use as adjunctive treatment for patients with partial-onset seizures. Dose-related adverse effects include somnolence, confusion and dizziness. Brivaracetam is the n-propyl analogue of levetiracetam. Mixed results have been obtained in phase III studies in patients with partial-onset seizures, and further trials in children, patients with photosensitive epilepsy and patients with partial-onset seizures are ongoing. Dizziness, headache and somnolence are the most common adverse effects reported. Perampanel was designed as an AMPA-type glutamate receptor antagonist. Following encouraging results from phase II studies in patients with refractory partial-onset seizures, recruitment for phase III trials is almost complete. Ganaxolone is a neurosteroid with potent antiepileptic activity that modulates GABA(A) receptors in the CNS. Ganaxolone has shown promise in a variety of seizure types. Dizziness and somnolence have been reported in some patients. The availability of new AEDs has widened the choices for clinicians treating patients with epilepsy. However, given the minimal improvement in prognosis and disappointing efficacy outcomes in double-blind, placebo-controlled, dose-ranging regulatory trials, it seems unlikely that these novel agents will have a major impact on outcomes for people with epilepsy.

Update on treatment of partial onset epilepsy: role of eslicarbazepine

Partial epilepsy comprises simple partial seizures, complex partial seizures, and secondarily generalized seizures, and covers more than 60% of patients with epilepsy. Antiepileptic drugs are generally considered to be the major therapeutic intervention for epilepsy but, despite a broad range of commonly used antiepileptic drugs, approximately 30% of adult patients and approximately 25% of children with epilepsy have inadequate seizure control. Eslicarbazepine acetate (ESL) is a novel voltage-gated sodium channel-blocking agent with presumed good safety and efficacy for adjunctive treatment of patients with drug-resistant partial epilepsy. ESL is a prodrug of eslicarbazepine (the active entity responsible for pharmacologic effects), and is rapidly and extensively hydrolyzed during first pass by liver esterases after oral administration. The half-life of eslicarbazepine at steady-state plasma concentrations is 20-24 hours, compatible with once-daily administration. ESL 800 mg and 1200 mg significantly reduces seizure frequency and shows a favorable safety profile in adult patients with drug-resistant partial-onset seizures, as demonstrated in previous Phase II and III trials. In children, ESL showed a clear dose-dependent decrease in seizure frequency with good tolerability. The most commonly reported adverse events associated with ESL are dizziness, somnolence, nausea, diplopia, headache, vomiting, blurred vision, vertigo, and fatigue. In conclusion, these characteristics suggest that ESL might be a valid and well tolerated treatment option for patients with drug-resistant partial-onset epilepsy. The convenience of once-daily dosing and a short, simple titration regimen would be of special interest for children, although conclusive published data are lacking to date. Hence, there is an urgent need to establish the therapeutic value of ESL in this special population in the near future.