Suvorexant

Introduction Overview

Generic Name

suvorexant

Brand Name

Belsomra

Dosage Form

tablets (5 mg, 10 mg, 15 mg, 20 mg)

Drug Class

Miscellaneous anxiolytics, sedatives and hypnotics; Dual orexin receptor antagonist (DORA)

Pharmacokinetics

Absorption

Suvorexant is rapidly absorbed following oral administration, with peak plasma concentrations typically achieved within 0.5 to 2.5 hours after dosing. Its rate of absorption can be delayed if taken with or soon after a high-fat meal, potentially delaying the onset of therapeutic effect. The drug exhibits a bioavailability influenced by food intake, therefore it is recommended to take suvorexant on an empty stomach or with minimal food to ensure rapid onset of action. The absolute oral bioavailability is approximately 82%.

Distribution

Suvorexant displays moderate volume of distribution, approximately 49 liters, indicating distribution into body tissues. It is highly bound to plasma proteins (>99.5%), primarily albumin, which may affect its interaction potential with other drugs. Due to its lipophilic nature, suvorexant readily crosses the blood-brain barrier to exert its pharmacologic effect centrally. Animal studies suggest moderate penetration into the central nervous system, consistent with its sedative action. Distribution is not significantly altered in elderly populations but may be affected in severe hepatic impairment.

Metabolism

Suvorexant is extensively metabolized in the liver primarily by cytochrome P450 enzymes CYP3A4 and to a lesser extent CYP2C19. The primary metabolic pathways include oxidative metabolism producing several metabolites, including hydroxylated and sulfone derivatives, which are largely inactive. Concomitant use of strong CYP3A inhibitors (such as ketoconazole, itraconazole) can significantly increase suvorexant plasma concentrations, requiring dosage adjustments or contraindication. Conversely, CYP3A inducers may decrease its efficacy by reducing plasma levels. Metabolic clearance is significantly reduced in hepatic impairment, necessitating dosage modification.

Elimination

Suvorexant and its metabolites are primarily eliminated via feces (approximately 66%) with the remainder excreted in urine (approximately 23%). The terminal elimination half-life ranges from 12 to 17 hours, supporting once-daily dosing at bedtime. Renal clearance is minimal, making suvorexant clearance relatively unaffected by renal impairment, though caution is advised. In patients with moderate hepatic impairment, elimination is compromised, leading to increased exposure, requiring dose adjustment. Population pharmacokinetic studies demonstrate no significant accumulation with repeated dosing when taken once nightly.

Dosage Forms

Adults

Belsomra is available as oral film-coated tablets in dosages of 5 mg, 10 mg, 15 mg, and 20 mg. The recommended starting dose for adults with insomnia is 10 mg taken once daily, no more than 30 minutes before bedtime, with at least 7 hours planned for sleep. If the 10 mg dose is well-tolerated but insufficiently effective, the dose can be increased to a maximum of 20 mg once daily. For patients concurrently using moderate CYP3A inhibitors, the starting dose is reduced to 5 mg with a maximum of 10 mg daily. Dose increases beyond these recommendations are not advised due to increased risk of side effects.

Adolescents

Belsomra is not approved for use in individuals under 18 years of age. Safety and efficacy have not been established in pediatric populations, therefore use in adolescents is not recommended at this time.

Special Populations

In patients with moderate hepatic impairment, dosage reductions are necessary due to increased systemic exposure; the maximum recommended dose is 10 mg once daily. Belsomra is not recommended in patients with severe hepatic impairment due to insufficient data and increased risk of adverse effects. In patients with mild to moderate renal impairment, no dosage adjustment is necessary as renal clearance is minimal. Use in pregnant or breastfeeding women requires careful consideration of benefits versus risks; animal studies indicate no direct teratogenicity but human data are limited. In elderly patients, no specific dose adjustment is required; however, caution is advised due to increased susceptibility to sedative effects and risk of next-day somnolence.

Mechanism Of Action

Suvorexant, the active ingredient in Belsomra, functions as a selective dual orexin receptor antagonist (DORA). It specifically binds to and blocks orexin receptors OX1R and OX2R located in the central nervous system. Orexin neuropeptides (orexin-A and orexin-B) are integral in promoting wakefulness and maintaining the sleep-wake cycle by activating these receptors. By antagonizing orexin receptor signaling, suvorexant reduces arousal, facilitating the initiation and maintenance of sleep.

At the molecular level, suvorexant's blockade of orexin receptors diminishes excitatory neurotransmission associated with wakefulness-promoting neurons in the hypothalamus and brainstem. This inhibition suppresses the activity of wake-promoting neurons such as histaminergic and noradrenergic neurons, thereby promoting sleep onset and enhancing sleep maintenance without the typical sedative or muscle relaxant effects seen with other hypnotics.

Clinically, the mechanism distinguishes suvorexant from traditional GABAergic hypnotics, leading to fewer impairments in motor coordination and memory function. This targeted approach correlates with improved sleep architecture, increasing both rapid eye movement and non-rapid eye movement sleep phases. Comparative studies demonstrate that suvorexant provides efficacy in reducing sleep latency and wake after sleep onset but with a distinct side effect profile due to its unique receptor targeting.

Extensive clinical trials confirm that suvorexant's orexin receptor antagonism leads to significant improvements in subjective and polysomnographic measures of sleep quality. Its mechanism offers a novel therapeutic avenue for insomnia that may reduce the risks associated with long-term use of traditional sedative-hypnotic agents.

Pharmacological Actions

Selective antagonism of orexin receptors OX1R and OX2R in the central nervous system
Promotion of sleep onset by inhibiting wakefulness pathways
Improvement of sleep maintenance and total sleep time
Reduction of sleep latency (time to fall asleep)
Enhancement of both REM and non-REM sleep quality
Minimal muscle relaxant and anxiolytic properties compared to benzodiazepines
No significant GABAergic receptor activity, reducing dependency potential vs traditional hypnotics
Controlled substance Schedule IV due to low but present risk of abuse
CNS depressant effects including sedation and somnolence
Potential to cause next-day drowsiness or impaired alertness if sleep duration is insufficient
Metabolic interactions via CYP3A affecting plasma concentrations
Does not provide anxiolytic or anti-depressive effects
May induce unusual sleep behaviors (e.g., sleepwalking) in some patients
Delayed onset of action if taken with or shortly after a high-fat meal

Therapeutic Clinical Uses

Treatment of insomnia characterized by difficulties in sleep onset and/or sleep maintenance
Improvement of sleep duration and continuity in adult patients
Management of chronic insomnia when non-pharmacologic therapies are inadequate
Alternative to traditional benzodiazepine or non-benzodiazepine hypnotics with lower abuse potential
Off-label research interest in alleviating sleep disturbances in psychiatric disorders (pending further evidence)
Not approved for narcolepsy or other hypersomnia disorders
Use limited to adults aged 18 years and older
Adjunct treatment in patients with comorbid conditions complicated by insomnia (with caution)
Potential benefit in insomnia patients with a history of substance abuse due to lower dependence risk

Side Or Adverse Effects

Somnolence or excessive daytime sleepiness
Unusual or vivid dreams and nightmares
Next-day impaired alertness or drowsiness
Sleep paralysis or hypnagogic hallucinations
Complex sleep behaviors including sleepwalking, sleep-driving, or engaging in activities while not fully awake with amnesia
Headache
Dizziness
Dry mouth
Fatigue and weakness
Anxiety or agitation in some patients
Confusion and memory disturbances
Possible allergic reactions including rash, itching, or swelling
Rare reports of paralysis or difficulty moving/talking upon waking
Potential for drug dependence or withdrawal symptoms after chronic use
Increased risk of falls or injuries in elderly patients due to CNS depression

Precautions

Use cautiously in patients with a history of substance abuse or addiction due to potential for abuse or dependence
Avoid concomitant use with other CNS depressants that may exacerbate sedation
Not recommended for patients with narcolepsy due to orexin pathway involvement
Use with caution in patients with depression, suicidal ideation, or mental health disorders
Monitor patients for emergence of behavioral changes such as aggression or hallucinations
Avoid driving or operating machinery within at least 8 hours of dosing due to risk of impaired alertness
Use cautiously in patients with respiratory disorders, including sleep apnea
Not established as safe in pregnancy and breastfeeding; weigh benefits against risks
Avoid alcohol consumption during treatment due to additive CNS depressant effects
Lower doses recommended in moderate hepatic impairment; avoid in severe impairment
Not studied in children and adolescents; safety and efficacy not established
Be vigilant for signs of allergic reactions or anaphylaxis
Do not exceed prescribed dose to prevent overdose risk
Monitor elderly for increased sensitivity to sedative effects and fall risk

Warnings

Do not exceed prescribed dose or frequency; overdose may lead to severe CNS depression or death
Avoid use if you have narcolepsy or excessive daytime sleepiness related to orexin deficiency
May cause complex sleep behaviors with amnesia including sleep-driving, sleep-eating, and others
Risk of next-day somnolence affecting activities requiring alertness such as driving
Use with caution in patients with history of depression or suicidal ideation
Risk of CNS depression is increased with concomitant CNS depressants or alcohol
If unusual behavioral changes, memory loss, or hallucinations occur, discontinue drug and seek medical advice
Not recommended for use in pregnancy or during breastfeeding without medical supervision
Schedule IV controlled substance; misuse can lead to addiction or dependence
Patients should have at least 7 hours allocated for sleep before dosing
Withdrawal symptoms or rebound insomnia may occur on abrupt discontinuation
Monitor for respiratory depression in patients with compromised pulmonary function

Contraindications

Known hypersensitivity or allergy to suvorexant or any component of Belsomra formulation
Patients diagnosed with narcolepsy due to orexin receptor antagonism
Use of strong CYP3A4 inhibitors concomitantly (e.g., ketoconazole, itraconazole) due to increased drug levels and risk of toxicity
Severe hepatic impairment where metabolism is impaired leading to increased exposure
Uncontrolled depression with suicidal ideation or history of suicidal behavior (relative contraindication)
Pediatric patients under 18 years of age; safety and efficacy not established
Patients who cannot allocate at least 7 hours for sleep after dosing
Known history of complex sleep behaviors induced by sedative medications

Drug Interactions

Strong CYP3A inhibitors (e.g., ketoconazole, itraconazole) significantly increase suvorexant plasma levels and are contraindicated
Moderate CYP3A inhibitors (e.g., erythromycin, diltiazem, verapamil) require dose adjustment and careful monitoring
CYP3A inducers (e.g., rifampin, carbamazepine) may reduce efficacy by lowering suvorexant levels
Concurrent use with other CNS depressants including opioids, benzodiazepines, barbiturates, muscle relaxants, antipsychotics, and alcohol may potentiate sedation and respiratory depression
Drugs affecting P-glycoprotein have minimal impact but caution advised
Potential additive sedative effects when combined with other hypnotics such as zolpidem or eszopiclone
Interactions with certain antidepressants or antiepileptics may alter plasma concentrations
Herbal supplements like St. John's Wort may reduce efficacy by inducing CYP3A4
Careful monitoring recommended when initiating or discontinuing interacting drugs
No significant food interactions besides delayed absorption with high-fat meals

Preparations Of The Drug

Oral film-coated tablets available in strengths of 5 mg, 10 mg, 15 mg, and 20 mg
Packaged in blister packs or bottles to protect from moisture and light
Tablet film coating includes excipients such as hypromellose, lactose monohydrate, titanium dioxide, and colorants varying by dosage strength
Inactive ingredients include croscarmellose sodium, lactose monohydrate, magnesium stearate, microcrystalline cellulose, and polyvinylpyrrolidone/vinyl acetate copolymer
Distributed by Merck Sharp & Dohme LLC
Stored at controlled room temperature 20°C to 25°C (68°F to 77°F)
Not scored tablets and not intended for splitting or crushing
Pack sizes vary including quantities for short-term outpatient therapy
Formulation designed for rapid dissolution and absorption for prompt onset of action