4.1. Therapeutic indications

Treatment of narcolepsy with cataplexy in adult patients, adolescents and children from the age of 7 years.

4.2. Posology and method of administration

Treatment should be initiated by and remain under the guidance of a physician experienced in the treatment of narcolepsy. Physicians should strictly adhere to the contraindications, warnings and precautions.

Posology

Adults

The recommended starting dose is 4.5 g/day sodium oxybate divided into two equal doses of 2.25 g/dose. The dose should be titrated to effect based on efficacy and tolerability (see section 4.4) up to a maximum of 9 g/day divided into two equal doses of 4.5 g/dose by adjusting up or down in dose increments of 1.5 g/day (i.e. 0.75 g/dose). A minimum of one to two weeks is recommended between dose increments. The dose of 9 g/day should not be exceeded due to the possible occurrence of severe symptoms at doses of 18 g/day or above (see section 4.4).

Single doses of 4.5 g should not be given unless the patient has been titrated previously to that dose level.

Discontinuation of Sodium Oxybate

The discontinuation effects of sodium oxybate have not been systematically evaluated in controlled clinical trials (see section 4.4).

If the patient stops taking the medicinal product for more than 14 consecutive days, titration should be restarted from the lowest dose.

Special populations

Elderly

Elderly patients should be monitored closely for impaired motor and/or cognitive function when taking sodium oxybate (see section 4.4).

Hepatic impairment

The starting dose should be halved in all patients with hepatic impairment, and response to dose increments monitored closely (see section 4.4 and 5.2).

Renal impairment

All patients with impaired renal function should consider a recommendation to reduce sodium intake (see section 4.4).

Paediatric population

Adolescents and children from 7 years of age with a minimum body weight of 15kg:

Sodium oxybate is administered orally twice nightly. Dosing recommendations are provided in Table 1.

Table 1 Sodium Oxybate Recommended Dose Initiation and Titration for Paediatric Patients

Patient weight

Initial total daily dose

(taken in 2 divided doses)*

Titration regimen (to clinical effect)

Recommended maximum total daily dose

15kg - <20kg

≤ 1g/day

≤ 0.5g/day/week

0.2g/kg/day

20kg - <30kg

≤ 2g/day

≤ 1g/day/week

30kg - <45kg

≤ 3g/day

≤ 1g/day/week

≥45kg

≤ 4.5g/day

≤ 1.5g/day/week

9g/day

*At bedtime and 2.5 to 4 hours later. For children who sleep more than 8 hours per night, sodium oxybate may be given after bedtime, while the child is in bed, in two equally divided doses 2.5 to 4 hours apart.

The dose should be gradually titrated to effect based on efficacy and tolerability (see section 4.4). A minimum of one to two weeks is recommended between dosage increments. Sodium oxybate dose recommendations (initial dose, titration regimen and maximum dose) for paediatric patients are based on body weight. Therefore, patients should have their body weight checked at regular intervals especially during titration to ensure that the appropriate dose of sodium oxybate is administered.

The recommended maximum total daily dose is 0.2g/kg/day in paediatric patients weighing less than 45kg. For paediatric patients weighing 45kg or more the maximum total daily dose is 9g/day.

The safety and efficacy of sodium oxybate in children below 7 years of age has not been established and therefore sodium oxybate is not recommended below 7 years of age. Children below 15kg should not receive sodium oxybate.

Method of administration

Sodium oxybate should be taken orally upon getting into bed and again between 2.5 to 4 hours later. It is recommended that both doses of Sodium oxybate should be made up at the same time upon retiring to bed.

Sodium oxybate is provided for use with a graduated measuring syringe and two 90 ml dosing cups with child resistant caps. Each measured dose of Sodium oxybate must be dispensed into the dosing cup and diluted with 60 ml of water prior to ingestion.

Because food significantly reduces the bioavailability of sodium oxybate, both adult and paediatric patients should eat at least several (2-3) hours before taking the first dose of Sodium oxybate at bedtime. Adults and paediatric patients should always observe the same timing of dosing in relation to meals. Doses should be taken within 24 hours after preparation, or else discarded.

The patient should only use the syringe provided in the package of Sodium oxybate. Other sodium oxybate products with different strengths are available, and interchanging the different syringes of different brands can result in overdose. Serious adverse events such as respiratory depression, convulsion and psychosis could occur (see section 4.8 undesirable effects and section 4.9 overdose)

4.3. Contraindications

• Hypersensitivity to the active substance or to any of the excipients listed in section 6.1.

• Patients with major depression.

• Patients with succinic semialdehyde dehydrogenase deficiency.

• Patients being treated with opioids or barbiturates.

4.4. Special warnings and precautions for use

Sodium Oxybate has the potential to induce respiratory depression

Respiratory and CNS depression

Sodium oxybate also has the potential to induce respiratory depression. Patients should be assessed before treatment for sleep apnoea and caution should be exercised when considering treatment. Apnoea and respiratory depression have been observed in a fasting healthy subject after a single intake of 4.5 g (twice the recommended starting dose). During post-marketing surveillance, it has been observed that the use of sodium oxybate may predispose the patients to choking sensation during sleep. Patients should be questioned regarding signs of Central Nervous System (CNS) or respiratory depression. Special caution should be observed in patients with an underlying respiratory disorder. Patients should be monitored for signs of respiratory depression during treatment. Because of the higher risk of sleep apnoea, patients with a BMI ≥40 kg/m2 should be monitored closely when taking sodium oxybate.

Approximately 80% of patients who received sodium oxybate during clinical trials maintained CNS stimulant use. Whether this affected respiration during the night is unknown. Before increasing the sodium oxybate dose (see section 4.2), prescribers should be aware that sleep apnoea occurs in up to 50% of patients with narcolepsy.

Benzodiazepines

Given the possibility of increasing the risk of respiratory depression, the concomitant use of benzodiazepines and sodium oxybate should be avoided.

Alcohol and CNS depressants

The combined use of alcohol, or any CNS-depressant medicinal product, with sodium oxybate may result in potentiation of the CNS-depressant effects of sodium oxybate as well as increased risk of respiratory depression. Therefore, patients should be warned against the use of alcohol in conjunction with sodium oxybate.

Gamma hydroxybutyrate (GHB) dehydrogenase inhibitors

Caution is required in patients who are treated concomitantly with valproate or other GHB dehydrogenase inhibitors as pharmacokinetic and pharmacodynamic interactions have been observed when sodium oxybate is co-administered with valproate (see section 4.5).

If concomitant use is warranted, dose adjustment is to be considered. Additionally, patient response and tolerability should be carefully monitored and dose should be adapted accordingly.

Topiramate

There have been clinical observation(s) of coma and increased plasma GHB concentration after co-administration of sodium oxybate with topiramate. Therefore, patients should be warned against the use of topiramate in conjunction with sodium oxybate (section 4.5).

Abuse potential and dependence

Sodium oxybate, which is as the sodium salt of GHB, is a CNS depressant active substance with well-known abuse potential. Prior to treatment physicians should evaluate patients for a history of or susceptibility to drug abuse. Patients should be routinely monitored and in the case of suspected abuse, treatment with sodium oxybate should be discontinued.

There have been case reports of dependence after illicit use of GHB at frequent repeated doses (18 to 250 g/day) in excess of the therapeutic dose range. Whilst there is no clear evidence of emergence of dependence in patients taking sodium oxybate at therapeutic doses, this possibility cannot be excluded.

Patients with porphyria

Sodium oxybate is considered to be unsafe in patients with porphyria because it has been shown to be porphyrogenic in animals or in vitro systems.

Neuropsychiatric events

Patients may become confused while being treated with sodium oxybate. If this occurs, they should be evaluated fully, and appropriate intervention considered on an individual basis. Other neuropsychiatric events include anxiety, psychosis, paranoia, hallucinations, and agitation. The emergence of thought disorders including thoughts of committing violent acts (including harming others) and/or behavioural abnormalities when patients are treated with sodium oxybate requires careful and immediate evaluation.

The emergence of depression when patients are treated with sodium oxybate requires careful and immediate evaluation. Patients with a previous history of affective disorders (including depressive illness, anxiety and bipolar disorder), suicide attempt and psychosis should be monitored especially carefully for the emergence of depressive symptoms and/or suicidal ideation while taking sodium oxybate. Major depression is contraindicated for use with sodium oxybate (section 4.3).

If a patient experiences urinary or faecal incontinence during sodium oxybate therapy, the prescriber should consider pursuing investigations to rule out underlying aetiologies.

Sleepwalking has been reported in patients treated in clinical trials with sodium oxybate. It is unclear if some or all of these episodes correspond to true somnambulism (a parasomnia occurring during non-REM sleep) or to any other specific medical disorder. The risk of injury or self-harm should be borne in mind in any patient with sleepwalking. Therefore, episodes of sleepwalking should be fully evaluated and appropriate interventions considered.

Paediatric Population:

Monitoring during titration phase

The patient's tolerability, especially with regards to potential signs of central nervous system and respiratory depression, should be carefully monitored with each dose increase during titration. Careful monitoring should include that the parent/caregivers observe the child's breath after sodium oxybate intake to assess if there is any abnormality in breathing during the first two hours, for example rude breathing, sleep apnoea, cyanosis of lips/face. If abnormality in breathing is observed medical support should be sought. If any abnormality is noted after the first dose, the second dose should not be administered. If no abnormality is noted the second dose can be administered. The second dose should not be given earlier than 2.5 hours or later than 4 hours after the first dose. In individual cases, e.g. if it is uncertain that the parent/caregivers can manage careful monitoring as described, sodium oxybate is not recommended unless medical supervision of treatment can be organized.

If in doubt about administration of a dose, do not re-administer the dose to reduce the risk of overdose.

Weight Loss

Weight decrease is common amongst patients treated with sodium oxybate (see section 4.8). For paediatric patients it is important that their weight is checked at regular intervals especially during dose titration to ensure that the appropriate dose of sodium oxybate is being administered (see section 4.2).

Neuropsychiatric events

For children and adolescents extra care should be taken to assess any potential suicidal or depressive conditions before starting treatment with sodium oxybate (see section 4.8) and to monitor any treatment-emergent events.

Alcohol and CNS depressants

Given the risk of alcohol intake among adolescents, it is noted that alcohol may further increase the CNS and respiratory depressant effects of sodium oxybate in children – adolescents taking sodium oxybate (see section 4.5).

Sodium oxybate 500 mg/ml oral solution contains sodium.

This medicinal product contains 0.41 g of sodium per 2.25 g dose, corresponding to 20% of the WHO recommended maximum daily dietary sodium intake of 2 g for an adult.

The maximum daily dose of this medicine is 82% of the WHO recommended maximum daily intake of sodium for an adult. Sodium oxybate oral solution is considered high in sodium. This should be taken into account in people on sodium-controlled low salt diets. A recommendation to reduce sodium intake should be carefully considered in the management of patients with heart failure, hypertension or compromised renal function (see sections 4.2 and 4.9).

Elderly

There is very limited experience with sodium oxybate in the elderly. Therefore, elderly patients should be monitored closely for impaired motor and/or cognitive function when taking sodium oxybate.

Epileptic patients

Seizures have been observed in patients treated with sodium oxybate. In patients with epilepsy, the safety and efficacy of sodium oxybate has not been established, therefore use is not recommended.

Rebound effects and withdrawal syndrome

The discontinuation effects of sodium oxybate have not been systematically evaluated in controlled clinical trials. In some patients, cataplexy may return at a higher frequency on cessation of sodium oxybate therapy, however this may be due to the normal variability of the disease. Although the clinical trial experience with sodium oxybate in narcolepsy/cataplexy patients at therapeutic doses does not show clear evidence of a withdrawal syndrome, in rare cases, events such as insomnia, headache, anxiety, dizziness, sleep disorder, somnolence, hallucination, and psychotic disorders were observed after GHB discontinuation.

Educational Materials

In order to assist prescribers, and patients/caregivers about the important information for Sodium oxybate, educational materials will be provided to them. In particular the materials will reinforce that for paediatric patients, an initial assessment of the patient should be performed with regard to growth and learning ability and that in addition to any side effects, any behaviour changes (social and learning), should be reported to the child's healthcare provider.

4.5. Interaction with other medicinal products and other forms of interaction

The combined use of alcohol with sodium oxybate may result in potentiation of the central nervous system-depressant effects of sodium oxybate. Patients should be warned against the use of any alcoholic beverages in conjunction with sodium oxybate.

Sodium oxybate should not be used in combination with sedative hypnotics or other CNS depressants.

Sedative hypnotics

Drug interaction studies in healthy adults with sodium oxybate (single dose of 2.25 g) and lorazepam (single dose of 2 mg) and zolpidem tartrate (single dose of 5 mg) demonstrated no pharmacokinetic interactions. Increased sleepiness was observed after concomitant administration of sodium oxybate (2.25 g) and lorazepam (2 mg). The pharmacodynamic interaction with zolpidem has not been assessed. When higher doses up to 9 g/d of sodium oxybate are combined with higher doses of hypnotics (within the recommended dose range) pharmacodynamic interactions associated with symptoms of CNS depression and/or respiratory depression cannot be excluded (see section 4.3).

Tramadol

A drug interaction study in healthy adults with sodium oxybate (single dose of 2.25 g) and tramadol (single dose of 100 mg) demonstrated no pharmacokinetic/pharmacodynamic interaction. When higher doses up to 9 g/day of sodium oxybate are combined with higher doses of opioids (within the recommended dose range) pharmacodynamic interactions associated with symptoms of CNS depression and/or respiratory depression cannot be excluded (see section 4.3).

Antidepressants

Drug interaction studies in healthy adults demonstrated no pharmacokinetic interactions between sodium oxybate (single dose of 2.25 g) and the antidepressants protriptyline hydrochloride (single dose of 10 mg) and duloxetine (60 mg at steady state). No additional effect on sleepiness was observed when comparing single doses of sodium oxybate alone (2.25 g) and sodium oxybate (2.25 g) in combination with duloxetine (60 mg at steady state). Antidepressants have been used in the treatment of cataplexy. A possible additive effect of antidepressants and sodium oxybate cannot be excluded. The rate of adverse reactions has increased when sodium oxybate is co-administered with tricyclic antidepressants.

Modafinil

A drug interaction study in healthy adults demonstrated no pharmacokinetic interactions between sodium oxybate (single dose of 4.5 g) and modafinil (single dose of 200 mg). Sodium oxybate has been administered concomitantly with CNS stimulant agents in approximately 80% of patients in clinical studies in narcolepsy. Whether this affected respiration during the night is unknown.

Omeprazole

The co-administration of omeprazole has no clinically significant effect on the pharmacokinetics of sodium oxybate. The dose of sodium oxybate therefore does not require adjustment when given concomitantly with proton pump inhibitors.

Ibuprofen

Drug interaction studies in healthy adults demonstrated no pharmacokinetic interactions between sodium oxybate and ibuprofen.

Diclofenac

Drug interaction studies in healthy adults demonstrated no pharmacokinetic interactions between sodium oxybate and diclofenac. Co-administration of sodium oxybate and diclofenac in healthy volunteers reduced the attention deficit caused by the administration of Sodium oxybate alone as measured by psychometric tests.

GHB dehydrogenase inhibitors

Since sodium oxybate is metabolised by GHB dehydrogenase there is a potential risk of an interaction with medicinal products that stimulate or inhibit this enzyme (e.g. valproate, phenytoin or ethosuximide) (see section 4.4).

The co-administration of sodium oxybate (6 g per day) with valproate (1250 mg per day) resulted in an increase in systemic exposure to sodium oxybate by approximately 25% and no significant change in Cmax. No effect on the pharmacokinetics of valproate was observed. The resulting pharmacodynamic effects, including increased impairment in cognitive function and sleepiness, were greater with co-administration than those observed with either drug alone. If concomitant use is warranted, patient response and tolerability should be monitored and dose adjustments made if required.

Topiramate

Possible pharmacodynamic and pharmacokinetic interactions when sodium oxybate is used concomitantly with topiramate cannot be excluded as clinical observation(s) of coma, and increased plasma GHB concentration were reported in a patient(s) under concomitant use of sodium oxybate and topiramate (section 4.4).

Studies in vitro with pooled human liver microsomes indicate that sodium oxybate does not significantly inhibit the activities of the human isoenzymes (see section 5.2).

4.6. Fertility, pregnancy and lactation

Pregnancy

Animal studies have shown no evidence of teratogenicity but embryo lethality was seen in both rat and rabbit studies (see section 5.3).

Data from a limited number of pregnant women exposed in the first trimester indicate a possible increased risk of spontaneous abortions. To date no other relevant epidemiological data are available. Limited data from pregnant patients during second and third trimester indicate no malformative or foeto/neonatal toxicity of sodium oxybate.

Sodium oxybate is not recommended during pregnancy.

Breast-feeding

Sodium oxybate and/or its metabolites are excreted into breast milk. Changes in sleep patterns have been observed in breastfed infants from exposed mothers, which may be consistent with the effects of sodium oxybate on the nervous system. Sodium Oxybate should not be used during breastfeeding.

Fertility

There is no clinical data available on the effect of sodium oxybate on fertility. Studies in male and female rats at doses up to 1,000 mg/kg/day GHB have shown no evidence of an adverse effect on fertility.

4.7. Effects on ability to drive and use machines

Sodium oxybate has major influence on the ability to drive and use machines.

For at least 6 hours after taking sodium oxybate, patients must not undertake activities requiring complete mental alertness or motor co-ordination, such as operating machinery or driving.

When patients first start taking sodium oxybate, until they know whether this medicinal product will still have some carryover effect on them the next day, they should use extreme care while driving a car, operating heavy machines, or performing any other task that could be dangerous or require full mental alertness.

For paediatric patients, physicians and parents or caregivers are advised that if the daily dose to body weight ratio exceeds 0.1g/kg/day, the waiting time may be longer than 6 hours depending on individual sensitivity

4.8. Undesirable effects

Summary of the safety profile

Clinical studies

The safety profile was qualitatively the same in adult and paediatric studies.

In adults, the most commonly reported adverse reactions were dizziness, nausea, and headache, all occurring in 10% to 20% of patients. The most serious adverse reactions are suicidal attempt, psychosis, respiratory depression and convulsion.

In adults, the efficacy and safety of sodium oxybate for the treatment of narcolepsy symptoms was established in four multicentre, randomised, double-blind, placebo-controlled, parallel- group trials in patients with narcolepsy with cataplexy except for one trial where cataplexy was not required for enrolment. Two Phase 3 and one Phase 2 double-blind, parallel- group, placebo-controlled studies were performed to assess the indication of sodium oxybate for fibromyalgia in adults. Additionally, randomised, double-blind, placebo-controlled, crossover drug-drug interaction studies with ibuprofen, diclofenac and valproate were performed in healthy adult subjects and are summarised in section 4.5.

Post-marketing experience

In addition to the adverse reactions reported during clinical studies, adverse reactions have been reported in post-marketing experience. It is not always possible to reliably estimate the frequency of their incidence in the population to be treated.

Tabulated summary of adverse reactions

Undesirable effects are listed according to MedDRA System Organ Class.

Frequency estimate: very common (≥ 1/10); common (≥ 1/100 to < 1/10); uncommon (≥ 1/1000 to < 1/100); rare (≥ 1/10,000 to < 1/1000); very rare (< 1/10,000); not known (cannot be estimated from the available data).

Within each frequency grouping, adverse reactions are presented in order of decreasing seriousness.

Infections and infestations

Common: nasopharyngitis, sinusitis.

Immune system disorders

Uncommon: hypersensitivity.

Metabolism and nutrition disorders

Common: anorexia, decreased appetite.

Not known: Dehydration, increased appetite.

Psychiatric disorders

Common: depression, cataplexy, anxiety, abnormal dreams, confusional state, disorientation, nightmares, sleepwalking, sleep disorder, insomnia, middle insomnia, nervousness.

Uncommon: suicide attempt, psychosis, paranoia, hallucination, abnormal thinking, agitation, initial insomnia.

Not known: suicidal ideation, homicidal ideation, aggression, euphoric mood, sleep- related eating disorder, panic attack, mania / bipolar disorder, delusion, bruxism, irritability and increased libido.

Nervous system disorders

Very common: dizziness, headache.

Common: sleep paralysis, somnolence, tremor, balance disorder, disturbance in attention, hypoesthesia, paraesthesia, sedation, dysgeusia.

Uncommon: myoclonus, amnesia, restless legs syndrome.

Not known: convulsion, loss of consciousness, dyskinesia.

Eye disorders

Common: blurred vision.

Ear and labyrinth disorders

Common: vertigo.

Not known tinnitus.

Cardiac disorders

Common: palpitations.

Vascular disorders

Common: hypertension.

Respiratory, thoracic and mediastinal disorders

Common: dyspnoea, snoring, nasal congestion.

Not known: respiratory depression, sleep apnoea, choking sensation.

Gastrointestinal disorders

Very common: nausea (the frequency of nausea is higher in women than men).

Common: vomiting, diarrhoea, abdominal pain upper.

Uncommon: faecal incontinence.

Not known: dry mouth.

Skin and subcutaneous tissue disorders

Common: hyperhidrosis, rash.

Not known: urticaria, angioedema, seborrhea.

Musculoskeletal and connective tissue disorders

Common: arthralgia, muscle spasms, back pain.

Renal and urinary disorders

Common: enuresis nocturna, urinary incontinence.

Not known: pollakiuria / micturition urgency, nocturia.

General disorders and administration site conditions

Common: asthenia, fatigue, feeling drunk, oedema peripheral.

Investigations

Common: blood pressure increased, weight decreased.

Injury, poisoning and procedural complications

Common: fall.

Description of selected adverse reactions

In some patients, cataplexy may return at a higher frequency on cessation of sodium oxybate therapy, however this may be due to the normal variability of the disease. Although the clinical trial experience with sodium oxybate in narcolepsy/cataplexy patients at therapeutic doses does not show clear evidence of a withdrawal syndrome, in rare cases, adverse reactions such as insomnia, headache, anxiety, dizziness, sleep disorder, somnolence, hallucination, and psychotic disorders were observed after GHB discontinuation.

Special Populations

Paediatric population

In the paediatric population the efficacy and safety of sodium oxybate for the treatment of narcolepsy with cataplexy symptoms was established in a phase 2/3 double-blind, placebo-controlled, randomized-withdrawal multicenter study.

In a study in children and adolescents the most frequently reported related TEAEs were enuresis (18.3%), nausea (12.5%), vomiting (8.7%), and weight decreased (8.7%), decreased appetite (6.7%), headache (5.8%), dizziness (5.8%). Adverse drug reactions of suicidal ideation (1%) and of acute psychosis (1%) were also reported. (see section 4.4 and section 5).

In some children between 7 and < 18 years, postmarketing surveillance has shown that sodium oxybate was discontinued due to abnormal behaviour, aggression and mood alteration.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

4.9. Overdose

Information about signs and symptoms associated with overdose with sodium oxybate is limited. Most data derives from the illicit use of GHB. Sodium oxybate is the sodium salt of GHB. Events associated with withdrawal syndrome have been observed outside the therapeutic range.

Symptoms

Patients have exhibited varying degrees of depressed consciousness that may fluctuate rapidly between a confusional, agitated combative state with ataxia and coma. Emesis (even with impaired consciousness), diaphoresis, headache, and impaired psychomotor skills may be observed. Blurred vision has been reported. An increasing depth of coma has been observed at higher doses as well as acidosis. Myoclonus and tonic-clonic seizures have been reported. There are reports of compromise in the rate and depth of respiration and of life- threatening respiratory depression, necessitating intubation and ventilation. Cheyne- Stokes respiration and apnoea have been observed. Bradycardia and hypothermia may accompany unconsciousness, as well as muscular hypotonia, but tendon reflexes remain intact. Bradycardia has been responsive to atropine intravenous administration. Events of hypernatremia with metabolic alkalosis have been reported in the context of concomitant use of NaCl infusion.

Management

Gastric lavage may be considered if co-ingestants are suspected. Because emesis may occur in the presence of impaired consciousness, appropriate posture (left lateral recumbent position) and protection of the airway by intubation may be warranted.

Although gag reflex may be absent in deeply comatose patients, even unconscious patients may become combative to intubation, and rapid sequence induction (without the use of sedative) should be considered.

No reversal of the central depressant effects of sodium oxybate can be expected from flumazenil administration. There is insufficient evidence to recommend the use of naloxone in the treatment of overdose with GHB. The use of haemodialysis and other forms of extracorporeal medicinal product removal have not been studied in sodium oxybate overdose, but has been reported in cases of acidosis due to GHB overdose. However, due to the rapid metabolism of sodium oxybate, these measures may not be warranted.