Sodium oxybate for the treatment of narcolepsy

Randomized, crossover, open-label study of the relative bioavailability and safety of FT218, a once-nightly sodium oxybate formulation: Phase 1 study in healthy volunteers

OBJECTIVES

Treatment for narcolepsy with sodium oxybate (SXB) has required twice-nightly dosing, at bedtime and 2.5-4 h later. This study evaluated the pharmacokinetics of FT218, an investigational, extended-release, once-nightly formulation of SXB (ON-SXB), vs twice-nightly SXB.

METHODS

In this phase 1, open-label study, healthy volunteers were randomized (1:1) to ON-SXB 6 g or twice-nightly SXB (two 3-g doses administered 4 h apart); minimum 3-day washout before crossover. Doses were administered 2 h post-evening meal. Blood samples for pharmacokinetic assessments were collected predose and up to 14 h after the first dose during each treatment period.

RESULTS

Twenty-eight participants were enrolled (mean age, 39.6 years; 54% women; 93% white). Mean ± SEM area under the concentration-time curve for ON-SXB was 282.7 ± 30.2  μg·h/mL vs 273.3 ± 27.8 μg·h/mL for twice-nightly SXB. Geometric mean ratio (GMR; 90% CI) was 102.9 (98.0-108.0). Maximum γ-hydroxybutyrate (GHB) plasma concentration (C_max) was 65.8 ± 4.0 μg/mL for ON-SXB vs 77.1 ± 4.9 μg/mL for twice-nightly SXB (GMR [90% CI], 88.3 [80.5-97.0]). The GMR (90% CI) for GHB plasma concentrations 8 h post dose (C_8h) for ON-SXB vs twice-nightly SXB was 61.7 (45.8-83.0). The most frequently reported adverse events were the same for ON-SXB and twice-nightly SXB (nausea, dizziness, somnolence, vomiting).

CONCLUSIONS

GHB exposure and C_max with one 6-g dose of ON-SXB were bioequivalent to those with two 3-g doses of twice-nightly SXB, whereas C_8h was lower with ON-SXB. If approved, ON-SXB will provide a single bedtime oxybate option, with clinically relevant pharmacologic exposure during the entire sleep period.

Population and Noncompartmental Pharmacokinetics of Sodium Oxybate Support Weight-Based Dosing in Children and Adolescents With Narcolepsy With Cataplexy

The pharmacokinetics (PKs) of sodium oxybate (SXB) was evaluated in a subset of participants from a study of SXB treatment in children (aged 7–11 years; n = 11) and adolescents (aged 12–17 years; n = 18) with narcolepsy with cataplexy. PK evaluation was conducted over 2 nights during the period when participants received a stable nightly SXB dose. The SXB dose on night 1 was half of night 2 and was administered in two equally divided doses: dose 1 was administered > 2 hours after the evening meal, and dose 2 was administered ≥ 4 hours after dose 1. Noncompartmental PK analysis demonstrated higher plasma concentrations post‐dose 2 vs. post‐dose 1, higher than dose‐proportional increases in area under the concentration‐time curve from 0 to 4 hours (AUC_0–4h) after dose 1, indicating nonlinear clearance, and better correlation between exposure and mg/kg than exposure and gram dose. To confirm the noncompartmental findings, identify factors affecting SXB PK, and compare with prior results in adults, a population PK (PopPK) model was established combining PK data from the current study with prior data from adults (132 healthy volunteers and 13 with narcolepsy). A two‐compartment PopPK model with first‐order absorption and nonlinear clearance from the central compartment described the data well. PopPK identified weight as the main intrinsic factor and food as the main extrinsic factor affecting SXB PK, and predicts similar PK profiles on a mg/kg basis across ages. These results, along with previously reported efficacy and safety outcomes, support weight‐based SXB dose initiation in pediatric patients.

Formulary Forum: Sodium Oxybate for Cataplexy

Objective:

To review the pharmacology, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, precautions, dosing recommendations, and patient counseling of sodium oxybate for the treatment of cataplexy in patients with narcolepsy.

Data Sources:

OVID and PubMed databases were searched (1966–January 2006) using the key words sodium oxybate, gamma-hydroxybutyrate, narcolepsy, and cataplexy. Only English-language articles were selected.

Study Selection and Data Extraction:

All information on sodium oxybate related to narcolepsy and cataplexy was considered. Study selection included human trials evaluating safety and efficacy of sodium oxybate for the treatment of cataplexy.

Data Synthesis:

Sodium oxybate is approved by the Food and Drug Administration for the treatment of excessive daytime sleepiness and cataplexy in patients with narcolepsy. In placebo-controlled trials, sodium oxybate demonstrated efficacy in reducing the number of cataplexy attacks. The dosing regimen includes a split dose given at bedtime and 2.5–4 hours later due to its short elimination half-life. The drug is generally well tolerated, with headache, nausea, dizziness, pain, and somnolence being the most common adverse events.

Conclusions:

Sodium oxybate is safe and effective for the treatment of cataplexy. Potential disadvantages include a multiple dosing regimen, abuse potential, cost, and a closed distribution system. Potential advantages demonstrated in clinical trials include significant decreases in the number of weekly cataplexy attacks, improvement in daytime sleepiness, and improvement in the Clinical Global Impression of Change score and nighttime awakenings. Overall, sodium oxybate provides a new option for the treatment of cataplexy.

Sodium oxybate in the treatment of childhood narcolepsy-cataplexy: a retrospective study

OBJECTIVE

To evaluate the efficacy and side effect profile of sodium oxybate in the treatment for narcolepsy-cataplexy in the pediatric age group.

METHODS

A retrospective study was conducted on 15 children and adolescents with narcolepsy-cataplexy who had been treated with sodium oxybate. The mean age at diagnosis of narcolepsy was 11 years (range 3-17 years). Subjects were followed for 3-90 months (mean 33) after starting sodium oxybate. During this period of time they were also maintained on other medications for sleepiness (n=14) and cataplexy (n=6). The charts were reviewed for documentation of improvement in sleepiness or cataplexy, side effects, and functioning in daily life.

RESULTS

Subsequent to the addition of sodium oxybate, sleepiness improved in 13/15 patients. In patients who had Epworth Sleepiness Scale (ESS) assessments, the score fell from a baseline median of 18 to 12 (n=10, p=0.01). The number of cataplexy episodes estimated by parents decreased from a median of 38/week pre-treatment to <1/week post treatment (n=14, p<0.001). Cataplexy severity, measured on an arbitrary scale, fell from a median of 3 (severe) to 1 (mild) in all 15 subjects (p<0.001). Two of the 15 patients (13%) discontinued sodium oxybate, one for insurance reasons and the other due to constipation and dissociative feelings. A third patient stopped the medication temporarily due to body aches and dizziness, but then resumed treatment without recurrence of symptoms. Side effects in four others included tremor, blurring of vision, nocturnal awakenings, and increased nightmares. Overall, side effects occurred in 6/15 (40%) individuals. Improvement in social/academic spheres was noted in 11/15 (73%) subjects after starting sodium oxybate. The median BMI before and after treatment remained unchanged at 23 (n=14, p=0.99). Median values of height and weight before and after treatment also did not change significantly. The mean dose of sodium oxybate was 5 ± 2 g. Dose escalation owing to development of tolerance was not encountered.

CONCLUSIONS

Sodium oxybate is effective in alleviating sleepiness and cataplexy in childhood onset narcolepsy-cataplexy. The therapeutic response was sustained over time, and without development of tolerance. Forty percent of the subjects experienced adverse effects.

Weight loss in narcolepsy patients treated with sodium oxybate

INTRODUCTION

Narcolepsy is often associated with increased body weight. Sodium oxybate has efficacy in many narcolepsy symptoms. The purpose of this study was to evaluate the effects of sodium oxybate on weight in patients with narcolepsy.

METHODS

Charts from three centers of all patients with narcolepsy who had been using sodium oxybate for at least 3 months were reviewed. Patients in whom anti-cataplexy medications were added or withdrawn or wake-promoting medications added after the start of sodium oxybate were excluded from further analysis. In the remainder, pre-sodium oxybate and, most recently, on-sodium oxybate weights were compared using Student's t-tests. Sodium oxybate dose and duration of therapy were also noted.

RESULTS

A total of 54 patients meeting inclusion criteria were identified. Of these 54, 33 (61%) were women; the mean age was 48.3 years. The mean dose of sodium oxybate was 6.9g/night and the duration of therapy was 25 months. The mean pre-sodium oxybate weight was 78.3 (+/-15.7)kg. The most recent on-sodium oxybate weight was 74.9 (+/-15.1, p=0.003). The average weight loss was 3.4kg, whereas the maximum was 30.9kg.

CONCLUSIONS

This study suggests that treatment of patients with narcolepsy with sodium oxybate can result in weight loss.

Pediatric narcolepsy

Narcolepsy is a disabling disease with a prevalence of 0.05%. It is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis, hypnogogic hallucinations, automatic behavior, and disrupted nocturnal sleep. The presentation can be very variable, making diagnosis difficult. Loss of hypocretin containing neurons in the lateral hypothalamus has been noted in autopsy studies, and the cerebrospinal fluid level of hypocretin is reduced in patients with narcolepsy with cataplexy. New treatment options are available for the many symptoms of this disease. Early recognition and treatment can greatly improve the quality of life of patients with narcolepsy. A detail review of the epidemiology, pathophysiology, and management of narcolepsy in children is presented.

Narcolepsy-cataplexy: how does recent understanding help in evaluation and treatment

Narcolepsy is a substantially disabling disease with profound physical, mental, and social effects. The burden on patients is compounded by delayed and missed diagnoses and by the subsequent undertreatment of narcolepsy and associated symptoms such as cataplexy. The recent advances in the elucidation of the genetics of canine narcolepsy and the pathophysiologic role of hypocretin, in animals and humans, enhances current diagnostic capability and will provide better treatment modalities in the future. The varied symptoms of narcolepsy are challenging to manage and may require treatment with a combination of agents. The recent development of a markedly enhanced characterization of sodium oxybate in the treatment of the excessive daytime sleepiness, nocturnal sleep fragmentation, and cataplexy of narcolepsy offers the potential of treating multiple symptoms simultaneously and marks a dramatic advance in the treatment of narcolepsy.

[The neurophysiology of cataplexy]

Cataplexy and excessive daytime sleepiness are the leading symptoms of narcolepsy. Electrophysiological studies in humans do not show a clear association between cataplexy and rapid eye movement (REM) sleep. Even a decrement of the H reflex is not specific for cataplexy and may be caused by unspecific triggers such as coughing. Cholinomimetics, which may induce status cataplecticus, do not influence REM sleep, thus evidencing a REM-independent mechanism. Recent studies demonstrate a lack of the neuropeptide hypocretin in the CSF of narcoleptics. Hypocretin controls wakefulness and the motor and autonomous systems. In hypocretin-1 and -2 knockout mice, sudden stops of motor activity could be observed in emotional situations that were accompanied by sudden shifts from wakefulness to REM sleep and could be terminated by application of anticataplectic medication. The lack of hypocretin not only causes a noradrenergic-cholinergic imbalance in the midbrain but also influences motoneurons directly by juxtacellular hypocretin-containing membranes. Intravenous application of hypocretin in a dog with hypocretin deficiency in the CSF caused a dose-dependent decrease of cataplexies. An understanding of the neuronal mechanisms responsible for cataplexies is essential for the development of new anticataplectic medications.