Pharmacotherapeutic group: antiepileptics, other antiepileptics; ATC code: N03AX26
Mechanism of action
Fenfluramine is a serotonin releasing agent, and thereby stimulates multiple 5‑HT receptor sub-types through the release of serotonin. Fenfluramine may reduce seizures by acting as an agonist at specific serotonin receptors in the brain, including the 5‑HT1D, 5‑HT2A, and 5‑HT2C receptors, and also by acting on the sigma‑1 receptor. The precise mode of action of fenfluramine in Dravet syndrome and Lennox-Gastaut syndrome is not known.
Clinical efficacy
Dravet syndrome
Children and young adults with Dravet syndrome
The effectiveness of fenfluramine in children and young adults with Dravet syndrome was evaluated in three randomised, multicentre, placebo-controlled studies (1501, 1502, 1504).
Study 1 (n=119) and Study 3 (n=143) are the prospective, merged analyses of the first 119 patients enrolled (Study 1) and the remaining subsequent total of 143 enrolled patients (Study 3) from 2 identical double-blind, placebo-controlled studies, ZX008-1501 and ZX008-1502. Study 1501 and Study 1502 were conducted in parallel and the design was identical: 3-arm, multicentre, randomised, double-blind, parallel group, placebo-controlled studies consisting of a 6-week baseline period followed by a 2-week titration period and a 12-week maintenance period for a total of 14-weeks treatment. Patients taking concomitant stiripentol were not enrolled in these studies. Eligible patients were randomised 1:1:1 to one of two doses of fenfluramine (0.7 mg/kg/day or 0.2 mg/kg/day, maximum 26 mg/day) or placebo. The mean (standard deviation) age of patients enrolled was 9.0 (4.7) years in Study 1 and was 9.3 (4.7) years in Study 3, with a range of 2 to 18 years. The majority of patients were ≥6 years of age (73.9% in Study 1 and 74.6% in Study 3). All enrolled patients were inadequately controlled on at least one anti-epileptic medicine, with or without vagal nerve stimulation and/or ketogenic diet, the most frequently used concomitant anti-epileptic medicines (≥25% overall) being valproate, clobazam, topiramate and levetiracetam.
Table 4. Dravet syndrome: Study 1 and Study 3 results of primary and selected secondary efficacy endpoints during maintenance period
| | Study 1 | Study 3 |
| | Placebo | Fenfluramine 0.2 mg/kg/day | Fenfluramine 0.7 mg/kg/day | Placebo | Fenfluramine 0.2 mg/kg/day | Fenfluramine 0.7 mg/kg/day |
| Convulsive Seizure Frequency during Maintenance period |
| CSF at Baseline, N, Median (per 28 days) (min, max) | 40 31.4 (3.3, 147.3) | 39 17.5 (4.8, 623.5) | 40 21.2 (4.9, 127.0) | 48 12.7 (4.0, 229.3) | 46 18.0 (4.0, 1464.0) | 48* 13.0 (2.7, 2700.7) |
| CSF at end of maintenance period. N, Median (min, max) | 39 25.7 (3.6, 204.7) | 39 17.1 (0.0, 194.3) | 40 4.9 (0, 105.5) | 48 10.6 (1.0, 139.0) | 46 7.6 (0.0, 2006.8) | 48 3.2 (0.0, 3651.7) |
| Reduction in mean monthly baseline-adjusted CSF compared to Placebo | - | 36.7% p=0.016 | 67.3% p<0.001 | - | 49.3% p< 0.0001 | 65.7% p< 0.0001 |
| % Reduction in convulsive seizures during Maintenance period |
| Number (%) of patients with ≥50% reduction in monthly convulsive seizures - change from baseline | 4 (10.3%) | 17 (43.6%) ES=33.3% RR: 4.25 | 29 (72.5%) ES=62.2% RR: 7.07 | 4 (8.3%) | 21 (45.7%) ES=37.3% RR: 5.48 | 33 (68.8%) ES=60.4% RR: 8.25 |
| Number (%) of patients with ≥75% reduction in monthly convulsive seizures - change from baseline | 2 (5.1%) | 10 (25.6%) ES=20.5% RR: 5.00 | 21 (52.5%) ES=47.4% RR: 10.24 | 2 (4.2%) | 9 (19.6%) ES=15.4% RR: 4.70 | 23 (47.9%) ES=43.7% RR: 11.50 |
| Number (%) of patients with ≥100% reduction in monthly convulsive seizures - change from baseline | 0 (0%) | 6 (15.4%) ES=15.4% | 6 (15.0%) ES=15.0% | 0 (0%) | 1 (2.2%) | 10 (20.8%) |
| Longest seizure-free interval during Titration + Maintenance period |
| Longest seizure-free interval (median) | 9.5 days | 15.0 days p=0.035 | 25.0 days p<0.001 | 10.0 days | 18.5 days p=0.0002 | 30 days p<0.0001 |
1 Effect size (ES) (Risk difference) calculated as proportion of Active-Placebo; RR: Relative Risk
*49 patients were enrolled and only 48 were administered with the treatment
Study 2 (previously known as 1504) (N=87) was a 2‑arm, multicentre, randomised, double-blind, parallel group, placebo-controlled study consisting of a 6‑week baseline period followed by a 3‑week titration period and a 12‑week maintenance period for a total of 15 weeks treatment. Eligible patients were randomised 1:1 to fenfluramine 0.4 mg/kg/day (maximum 17 mg/day) or placebo added to their stable standard of care regimen of stiripentol (plus clobazam and/or valproate) and possibly other anti‑epileptic medicines. The mean (standard deviation) age of patients enrolled in Study 2 was 9.1 (4.80) years, with a range of 2 to 19 years. The majority of patients were ≥6 years of age (72.4%) and the minority <6 years (27.6%), male (57.5%) and, where reported, white (59.8%). All enrolled subjects were inadequately controlled on at least one anti-epileptic medicine, which included stiripentol, with or without vagal nerve stimulation and/or ketogenic diet. The median baseline convulsive seizure frequency per 28 days was 10.7 and 14.0 in the placebo and fenfluramine 0.4 mg/kg/day groups, respectively.
Table 5. Dravet syndrome: Study 2 (previously known as Study ZX008-1504) results of primary and selected secondary efficacy endpoints during maintenance period
| | Study 2 |
| Placebo + stiripentol | Fenfluramine 0.4 mg/kg/day + stiripentol |
| Convulsive Seizure Frequency during Maintenance period |
| N Baseline. Median (min, max) | 44 10.7 (2.7, 162.7) | 43 14.3 (2.7, 213.3) |
| N At end of maintenance period. Median (min, max) | 44 11.4 (0.7, 169.3) | 42 3.9 (0.0, 518.0) |
| Reduction in mean monthly baseline-adjusted Convulsive Seizure Frequency compared to Placebo | - | 54.9 % p<0.001 |
| % reduction in convulsive seizures during Maintenance period |
| Number (%) of patients with ≥50% reduction in monthly convulsive seizures - change from baseline | 4 (9.1%) | 23 (54.8%) ES1=45.7 RR2: 6.02 |
| Number (%) of patients with ≥75% reduction in monthly convulsive seizures - change from baseline | 2 (4.5%) | 17 (40.5%) ES=36.0% RR: 8.90 |
| Number (%) of patients with ≥100% reduction in monthly convulsive seizures - change from baseline | 0 (0%) | 2 (4.8%) ES=4.8% |
| Longest seizure-free interval during Titration + maintenance period |
| Longest seizure-free interval (median) | 13.0 days | 22.0 days p=0.004 |
1 Effect size (ES) (Risk difference) calculated as proportion of Active-Placebo; 2 RR: Relative Risk
Adults
The Dravet syndrome population in Study 1, Study 2 and Study 3 was predominantly paediatric patients, with only 11 adult patients who were 18-19 years old (3.2%), and therefore limited efficacy and safety data were obtained in the adult Dravet syndrome population.
Open-label data
Dravet syndrome patients who participated in Study 1, Study 2 and Study 3 could participate in an open-label extension study (Study 5). The primary objective of the open-label extension (OLE) study was long-term safety of fenfluramine at doses of 0.2 to 0.7 mg/kg/day, whereby the dose of fenfluramine could be titrated to optimize treatment. Data are reported for 374 patients who participated in the open-label study and received fenfluramine for up to 3 years (median treatment period: 824 days; range: 7-1280). A median percentage change from Baseline in convulsive seizure frequency (CSF) during the overall OLE Treatment Period of -66.81% (p <0.001) was observed. Of 375 study participants, 12.8% discontinued the study due to lack of efficacy, 2.9% due to adverse events, 5.3% due to physician or family request.
Lennox-Gastaut syndrome
Children and adults with Lennox-Gastaut syndrome
The effectiveness of fenfluramine for the treatment of seizures associated with Lennox-Gastaut syndrome in patients 2 to 35 years of age was evaluated in a randomized, double-blind, placebo-controlled study (Study 4 Part 1). Part 1 includes 2 independently analyzed cohorts, Cohort A and Cohort B. Cohort A is the primary analysis cohort and includes subjects from North America, Europe, and Australia, and Cohort B includes subjects from Japan.
Study 4 Part 1 Cohort A
Study 4 Part 1 Cohort A compared a 0.7 mg/kg/day (N=87) and a 0.2 mg/kg/day (N=89) dose (up to a maximum dose per day of 26 mg) of fenfluramine with placebo (N=87). Patients had a diagnosis of Lennox-Gastaut syndrome and were inadequately controlled on at least one anti-epileptic medicine, with or without vagal nerve stimulation and/or ketogenic diet. The study had a 4-week baseline period, during which patients were required to have a minimum of 8 drop seizures while on stable anti-epileptic medicine therapy. Drop seizures included: generalized tonic-clonic, secondarily generalized tonic-clonic, tonic, atonic, or tonic-atonic seizures that were confirmed to result in drops. The baseline period was followed by randomization into a 2-week titration period and a subsequent 12-week maintenance period, where the dose of fenfluramine remained stable.
In Study 4 Part 1, 99% of patients were taking between 1 and 4 concomitant anti-epileptic medicines. The most frequently used concomitant anti-epileptic medicines (in at least 25% of patients) were clobazam (45.2%), lamotrigine (33.5%), and valproate (55.9%).
The primary efficacy endpoint in Study 4 Part 1 was percent change from baseline in the frequency of drop seizures per 28 days during the combined 14-week titration and maintenance periods (i.e., treatment period) in the fenfluramine 0.7 mg/kg/day group compared to the placebo group. Key secondary endpoints included the proportion of patients who achieve a ≥50% reduction from baseline in drop seizure frequency per 28 days for the fenfluramine 0.7 mg/kg/day group compared to the placebo group and proportion of patients who achieve improvement (minimally, much, or very much improved) in the Clinical Global Impression - Improvement (CGI-I) as assessed by the Principal Investigator for the fenfluramine 0.7 mg/kg/day group compared to the placebo group.
In Study 4 Part 1, the median percent change from baseline (reduction) in the frequency of drop seizures per 28 days was significantly greater for the fenfluramine 0.7 mg/kg/day group compared with the placebo group (Table 6). A reduction in drop seizures was observed within 2 weeks of initiating treatment with fenfluramine, and the effect remained consistent over the 14-week treatment period.
Among subjects with ≥124 drop seizures per 28 days during Baseline, the reduction in DSF were -19.98%, -7.37%, -11.21% for subjects in the fenfluramine 0.7 mg/kg/day group, 0.2 mg/kg/day group, and placebo group respectively.
Table 6 Lennox-Gastaut syndrome: Study 4 Part 1 Cohort A of primary and selected secondary efficacy endpoints during maintenance period
| | Study 4 Part 1 Cohort A |
| | Placebo (N = 87) | Fenfluramine 0.7 mg/kg/day (N = 87) |
| Percentage Change from BL in DSF During M |
| DSF Summary Statistics a |
| Median at BL | 53.00 | 82.00 |
| Median during M | 47.33 | 55.73 |
| Median Percentage Change from BL During M | ‑7.28 | ‑27.16 |
| Nonparametric Model b | | |
| p‑value for comparison with placebo | — | 0.0018 |
| HL Estimate for Median Difference (A-P) | | |
| Estimate (Std Err) | — | ‑20 (5.795) |
| 95% CI | — | -31.61, -8.89 |
| Percentage of Patients with ≥ 50% Reduction from BL in DSF (50% Responder Rate) During M |
| ≥ 50% reduction in DSF, n (%) | 11 (12.6) | 27 (31.4) |
| p‑value for comparison with placebo c | | 0.0044 |
| Percentage of Patients with Improvement d on the CGI-I Investigator Rating at End of M |
| Subjects with score 1, 2, or 3, n (%) | 27 (33.8) | 39 (48.8) |
| p-value vs placebo e | | 0.0567 |
ANCOVA = analysis of covariance; A-P = active group–placebo group; BL = Baseline Period; CGI I = Clinical Global Impression – Improvement; CI = confidence interval; DSF = drop seizure frequency per 28 days; HL = Hodges-Lehmann; Std Err = standard error; T+M = Titration and Maintenance Periods
a BL, T+M, and percentage change from BL in M values for seizure frequency per 28 days are presented in original scale.
b Results are based on a nonparametric ANCOVA model with treatment group (3 levels) and weight strata (< 37.5 kg, ≥ 37.5 kg) as factors, rank of BL seizure frequency as a covariate, and rank of percentage change from BL in seizure frequency during treatment (M) as response
c Based on a logistic regression model that included a categorical response variable (achieved percentage point reduction, yes or no), weight group strata (< 37.5 kg, ≥ 37.5 kg), and Baseline DSF as a covariate.
d Minimally, much, or very much improved
e Based on a Cochran-Mantel-Haenszel test comparing active treatment with placebo, after adjusting for weight strata
The median percent reduction from baseline in drop seizure frequency per 28 days for the lower dose of fenfluramine (0.2 mg/kg/day) during the Maintenance Period did not reach statistical significance compared to placebo (Median change between 0.2 group of patients and placebo in % change from baseline during Maintenance Period -11.48 [95% CI -26.61, 3.31]).
The seizure type with the greatest median percentage change from Baseline in the fenfluramine 0.7 mg/kg/day group relative to the placebo group was generalised tonic-clonic seizures (-45.7% fenfluramine 0.7 mg/kg/day [n=38] versus 3.7% placebo [n=38]).
Study 4 Part 1 Cohort B
This study compared a 0.7 mg/kg/day (N=11) and a 0.2 mg/kg/day (N=11) dose (up to a maximum dose per day of 26 mg) of fenfluramine with placebo (N=11).
The primary study endpoint was assessed from Part 1 Cohort A data only, due to the small size of Cohort B.
The results from Cohort B support the clinical benefit of fenfluramine reported for Cohort A for the adjunctive treatment of drop seizures associated with LGS in Japanese subjects.
Table 7: Lennox-Gastaut syndrome: Study 4 Part 1 Cohort B of primary and selected secondary efficacy endpoints during maintenance period
| | Study 4 Part 1 Cohort B |
| | Placebo (N = 11) | Fenfluramine 0.7 mg/kg/day (N = 11) |
| Primary Endpoint: Percentage Change from BL in DSF During M |
| DSF Summary Statistics a |
| Median at BL | 53.00 | 58.00 |
| Median during M | 51.90 | 31.86 |
| Median Percentage Change from BL During M | ‑18.18 | ‑45.07 |
| HL Estimate for Median Difference (A-P) |
| Estimate (Std Err) | | ‑25.54 (17.000) |
| 95% CI | | (-57.57, 9.07) |
| Key Secondary Endpoint: Percentage of Patients with ≥ 50% Reduction from BL in DSF (50% Responder Rate) During M |
| ≥ 50% reduction in DSF, n (%) | 1 (9.1%) | 4 (36.4%) |
ANCOVA = analysis of covariance; A-P = active group–placebo group; BL = Baseline Period; CI = confidence interval; DSF = drop seizure frequency per 28 days; HL = Hodges-Lehmann; Std Err = standard error; M = Maintenance Period
a BL, M, and percentage change from BL in M values for seizure frequency per 28 days are presented in original scale.
Open-label data
Lennox-Gastaut patients who completed Study 4 Part 1 (ZX008-1601) could participate in Part 2, an open-label, 52-week, flexible-dose extension study. The primary objective of Study 4 Part 2 was to assess the long-term safety and tolerability of fenfluramine at doses of 0.2 mg/kg/day to 0.7 mg/kg/day. 279 patients were enrolled in the open label extension study received fenfluramine 0.2 mg/kg/day for 1 month, then the dose was titrated to optimize treatment. The safety data from open-label phase of Study 4 are consistent with known safety profile of fenfluramine.
Among the 177 LGS subjects treated with fenfluramine for ≥ 12 months, 24.3% received a fenfluramine mean daily dose of >0 to <0.4 mg/kg/day, 45.2% had received a fenfluramine mean daily dose of 0.4 to <0.6 mg/kg/day, and 30.5% received a fenfluramine mean daily dose ≥ 0.6 mg/kg/day.
The most common reason for discontinuation during the open label extension study was lack of efficacy (58 [20.8%]), adverse event (15 [5.4%]), and withdrawal by subject (17 [6.1%]).
Paediatric population
The European Medicines Agency has deferred the obligation to submit the results of studies with Fintepla in one or more subsets of the paediatric population in Dravet syndrome (see section 4.2 for information on paediatric use).