Pharmacotherapeutic group: Antiepileptics, carboxamide derivatives, ATC code: N03AF04
Mechanism of action
The precise mechanisms of action of eslicarbazepine acetate are unknown. However, in vitro electrophysiological studies indicate that both eslicarbazepine acetate and its metabolites stabilise the inactivated state of voltage-gated sodium channels, precluding their return to the activated state and thereby preventing repetitive neuronal firing.
Pharmacodynamic effect
Eslicarbazepine acetate and its active metabolites prevented the development of seizures in nonclinical models predictive of anticonvulsant efficacy in man. In humans, the pharmacological activity of eslicarbazepine acetate is primarily exerted through the active metabolite eslicarbazepine.
Clinical efficacy
Adult population
The efficacy of eslicarbazepine acetate as adjunctive therapy has been demonstrated in four phase III double- blind placebo-controlled studies in 1703 randomized adult patients with partial epilepsy refractory to treatment with one to three concomitant antiepileptic medicinal products. Oxcarbazepine and felbamate were not allowed as concomitant medicinal products in these studies. Eslicarbazepine acetate was tested at doses of 400 mg (in -301 and -302 studies only), 800 mg and 1200 mg, once daily. Eslicarbazepine acetate 800 mg once daily and 1200 mg once daily were significantly more effective than placebo in reducing seizure frequency over a 12-week maintenance period. The percentage of subjects with ≥50% reduction (1581 analyzed) in seizure frequency in the phase III studies was 19.3% for placebo, 20.8% for eslicarbazepine acetate 400 mg, 30.5% for eslicarbazepine acetate 800 mg and 35.3% for eslicarbazepine acetate 1200 mg daily.
The efficacy of eslicarbazepine acetate as monotherapy has been demonstrated in a double-blind, active controlled (carbamazepine controlled release) study, involving 815 randomized adult patients with newly diagnosed partial-onset seizures. Eslicarbazepine acetate was tested at once-daily doses of 800 mg, 1200 mg and 1600 mg. The doses of the active comparator, carbamazepine controlled release, were 200 mg, 400 mg and 600 mg, twice-daily. All subjects were randomized to the lowest dose level and only if a seizure occurred subjects were to be escalated to the next dose level. From the 815 randomized patients, 401 patients were treated with eslicarbazepine acetate once-daily [271 patients (67.6%) remained at dose of 800 mg, 70 patients (17.5%) remained at dose of 1,200 mg and 60 patients (15.0%) were treated with 1600 mg]. In the primary efficacy analysis, in which drop-outs were considered as non-responders, 71.1% subjects were classified as seizure free in the eslicarbazepine acetate group and 75.6% in the carbamazepine controlled release group during the 26 week evaluation period (average risk difference -4.28%, 95% confidence interval: [-10, 30; 1,74]. The treatment effect observed during the 26-week evaluation period was maintained over 1 year of treatment with 64.7 % eslicarbazepine acetate subjects and 70.3 % carbamazepine controlled release subjects classified as seizure free (average risk difference -5.46%, 95% confidence interval: [-11.88; 0.97]. In the analysis of treatment failure (seizure risk) based on time to event analysis (Kaplan-Meier analysis and Cox regression), the Kaplan-Meier estimates of seizure risk at the end of the evaluation period was 0.06 with carbamazepine and 0.12 with eslicarbazepine acetate and by the end of 1 year with an additional increased risk to 0.11 with carbamazepine and 0.19 with eslicarbazepine acetate (p=0.0002).
At 1 year, the probability for subjects to withdraw due to either adverse reactions or lack of efficacy was 0.26 for eslicarbazepine acetate and 0.21 for carbamazepine controlled release.
The efficacy of eslicarbazepine acetate as conversion to monotherapy was evaluated in 2 double-blind, randomized controlled studies in 365 adult patients with partial-onset seizures. Eslicarbazepine acetate was tested at doses of 1,200 mg and 1,600 mg once-daily. Seizure-free rates during the entire 10-week monotherapy period were 7.6% (1,600 mg) and 8.3 % (1,200 mg) in one study and 10.0% (1600 mg) and 7.4 % (1200 mg) in the other study, respectively.
Elderly population
The safety and efficacy of eslicarbazepine acetate as adjunctive therapy for partial seizures in elderly patients were evaluated in one non-controlled study, with a duration of 26 weeks, in 72 elderly (aged ≥ 65 years). The data shows that the incidence of adverse reactions in this population (65.3 %) is similar to the general population enrolled in the double-blind epilepsy studies (66.8%).The most frequent individual adverse reactions were dizziness (12.5% of subjects), somnolence (9.7%), fatigue, convulsion and hyponatraemia (8.3%, each), nasopharyngitis (6.9%) and upper respiratory tract infection (5.6%). A total of 50 of the 72 subjects starting the study completed the 26-week treatment period that corresponds to a retention rate of 69.4% (see section 4.2 for information on elderly use). There is limited data on monotherapy regimen available in the elderly population. Only a few subjects (N=27) aged above 65 years were treated with eslicarbazepine acetate in monotherapy study.
Paediatric population
The efficacy and safety of eslicarbazepine acetate as adjunctive therapy for partial-onset seizures in children was evaluated in one phase II study in children aged from 6 to 16 years (N=123) and one phase III study in children aged from 2 to 18 years (N=304). Both studies were double-blind and placebo controlled with a duration of maintenance of 8 weeks (study 208) and 12 weeks (study 305), respectively. Study 208 included 2 additional subsequent long-term, open-label extensions (1 year in part II and 2 years in part III) and Study 305 included 4 subsequent long-term, open-label extension periods (1 year in Parts II, III and IV and 2 years in Part V). Eslicarbazepine acetate was tested at doses of 20 and 30 mg/kg/day, up to a maximum of 1200 mg/day. The target dose was 30 mg/kg/day in study 208 and 20 mg/kg/day in study 305. Doses could be adjusted based on tolerability and treatment response.
In the double-blind period of the phase II study, evaluation of efficacy was a secondary objective. The least square mean reduction in standardised seizure frequency from baseline to maintenance period was significantly (p<0.001) higher with eslicarbazepine acetate (-34.8%) compared to placebo (-13.8%). Forty-two patients (50.6%) in the eslicarbazepine acetate group compared to 10 patients (25.0%) in the placebo group were responders (≥50% reduction of standardised seizure frequency), resulting in a significant difference (p=0.009).
In the double-blind period of the phase III study, the least square mean reduction in standardised seizure frequency with eslicarbazepine acetate (-18.1% versus baseline) was different to placebo (-8.6% versus baseline) but not statistically significant (p=0.2490). Forty-one patients (30.6%) in the eslicarbazepine acetate group compared to 40 patients (31.0%) in the placebo group were responders (≥50% reduction of standardised seizure frequency), resulting in a non-significant difference (p=0.9017). Post-hoc subgroup analyses for the phase III study were conducted by age strata and above 6 years, as well as by dose.. In children above 6 years, 36 patients (35.0%) in the eslicarbazepine acetate group compared to 29 patients (30.2%) in the placebo group were responders (p=0.4759) and the least square mean reduction in standardised seizure frequency was higher in the eslicarbazepine acetate group compared to placebo (-24.4% versus -10.5%); however, the difference of 13.9% was not statistically significant (p=0.1040). A total of 39% patients in study 305 were up titrated to the maximum possible dose (30 mg/kg/day). Amongst these, when excluding patients aged 6 years and younger, 14 (48.3%) and 11 (30.6%) of patients in the eslicarbazepine acetate and placebo group, respectively, were responders (p=0.1514). Although the robustness of these post-hoc subgroup analyses is limited, the data suggest an age and dose dependent increase in effect size.
In the subsequent 1-year open-label extension (Part II) of the phase III study (ITT set N=225) the total responder rate was 46.7% (steadily increasing from 44.9% (weeks 1-4) to 57.5% (weeks > 40)). The total median standardised seizure frequency was 6.1 (decreasing from 7.0 (weeks 1-4) to 4.0 (weeks > 40), resulting in a median relative change compared to the baseline period of -46.7%). The median relative change was larger in the previous placebo group (-51.4%) than in the previous ESL group (- 40.4%). The proportion of patients with exacerbation (increase of ≥25%) compared to the baseline period was 14.2%.
In the subsequent 3 open-label extensions (ITT set N=148), the overall responder rate was 26.6% when compared to baseline Parts III–V (i.e. the last 4 weeks in part II). The total median standardised seizure frequency was 2.4 (resulting in a median relative change from Baseline Part III–V of -22.9%). The overall median relative decrease in Part I was greater in patients treated with ESL (-25.8%) than in patients treated with placebo (-16.4%). The overall proportion of patients with exacerbation (increase of ≥25%) compared to Baseline Parts III–V was 25.7%.
Of the 183 patients who completed parts I and II of the study, 152 patients were enrolled into part III. Of these, 65 patients had received ESL and 87 patients had received placebo during the double-blind part of the study. 14 patients (9.2%) completed open-label treatment with ESL through Part V. The most common reason for withdrawal during any part of the study was sponsor request (30 patients in part III [19.7% of the patients who entered part III], 9 in part IV [9.6% of the patients who entered part IV], and 43 in part V [64.2% of the patients who entered Part V]).
Taking into consideration the limitations of open label uncontrolled data, the long-term response to eslicarbazepine acetate in the open-label parts of the study was overall maintained.
The European Medicines Agency has deferred the obligation to submit the results of studies with eslicarbazepine acetate in one or more subsets of the paediatric population in the treatment of epilepsy with partial onset seizures (see section 4.2 for information on paediatric use).