Pitolisant: Selective Histamine H3 Receptor Inverse Agonist for Narcolepsy
Pitolisant (trade name Wakix, Bioprojet) is the first selective histamine H3 receptor inverse agonist and was approved in Europe in 2016 for the treatment of narcolepsy with or without cataplexy. In 2019, the indication was expanded to include narcolepsy in children aged 6 years and over. Pitolisant represents an important innovation in narcolepsy therapy because it offers a new mechanism of action and, unlike classic stimulants (modafinil, methylphenidate, amphetamines), is not subject to controlled substance regulations.
Narcolepsy is a rare, chronic neurological disorder characterised by daytime sleepiness, sudden sleep attacks, cataplexy (brief emotion triggered muscle weakness), sleep paralysis and hypnagogic hallucinations. The condition is usually associated with a deficiency of hypocretin (orexin) in the hypothalamus, often of autoimmune origin. Pitolisant increases the activity of the histaminergic wake system and thereby improves both daytime sleepiness and cataplexy.
Mechanism of Action
Pitolisant is a selective inverse agonist at the H3 histamine autoreceptor on histaminergic neurons in the posterior hypothalamus. H3 receptors function as presynaptic autoreceptors and heteroreceptors, negatively regulating histamine synthesis and release. Through inverse agonist binding, the constitutive activity of the receptor is inhibited, which increases histamine synthesis and release in downstream brain regions.
Histamine in the brain is one of the central wake neurotransmitters. In narcolepsy, histaminergic activity is reduced due to hypocretin deficiency. Pitolisant action partially compensates for this reduction and improves wakefulness. In addition, pitolisant indirectly modulates the activity of other wake neurotransmitters such as acetylcholine and noradrenaline.
Pharmacokinetically, pitolisant is orally absorbed with a bioavailability of approximately 56 percent, half life 10 to 12 hours, allowing once daily administration. Metabolism via CYP2D6 and CYP3A4. Active metabolites prolong the action.
Indications
- Narcolepsy with or without cataplexy in adults: first line therapy according to EFNS and AASM recommendations
- Narcolepsy in children aged 6 years and over: approved since 2019
- Obstructive sleep apnoea syndrome (OSAS) with residual daytime sleepiness despite CPAP: approved 2019, but reimbursement limited in Germany
- Off label: idiopathic hypersomnia, daytime sleepiness in Parkinson's disease, restless legs associated sleep disorder
Dosage and Administration
Adults: initial dose 9 mg in the morning for 1 week, then 18 mg in the morning for 1 week, then increase up to maximum dose of 36 mg in the morning depending on efficacy and tolerability.
Children aged 6 and over: dose graduated by body weight, initial dose 4.5 mg, gradual increase.
Administration: once daily in the morning with breakfast, ideally at the same time of day. Late administration after midday can cause sleep disturbances.
In moderate to severe renal insufficiency: maximum dose 18 mg. In moderate hepatic insufficiency: maximum dose 18 mg, severe hepatic insufficiency is contraindicated.
In CYP2D6 poor metabolisers: lower maximum dose (18 mg) due to higher levels.
Adverse Effects
Common: sleep disturbance (insomnia), headache, nausea, anxiety, irritability, dizziness, fatigue, dry mouth.
Occasional: depression, mood swings, tachycardia, hot flushes, tinnitus, hearing impairment, weight gain or loss.
Rare but important: QT prolongation with risk of arrhythmias, severe allergic reactions, increased liver transaminases, seizures in at risk patients.
Important: patients should be monitored for psychiatric symptoms (depression, suicidal thoughts, aggression) during treatment and inform the treating practice. In cardiac risk factors or pre existing QT prolongation, an ECG before therapy and during follow up is advisable.
Interactions
- Hormonal contraceptives: pitolisant can reduce efficacy, alternative or additional non hormonal contraception is recommended during therapy and 21 days afterwards
- Tricyclic antidepressants, mirtazapine, anti H1 antihistamines: antagonistic effect at the histamine receptor, can attenuate pitolisant action
- Strong CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine): increased pitolisant levels, maximum dose 18 mg
- Strong CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St. John's wort): reduced pitolisant levels, action may decrease
- QT prolonging substances: additive QT prolongation
Special Considerations
Pregnancy and breastfeeding: data are limited; use during pregnancy only on clear indication. During treatment, reliable contraception is recommended, since hormonal contraception may be less reliable. During breastfeeding, use is not recommended.
Before starting therapy: ECG to assess QT, liver transaminases, history of psychiatric and cardiac comorbidities.
Diagnosis of narcolepsy: treatment with pitolisant is undertaken after confirmed diagnosis of narcolepsy by specialist sleep medicine (polysomnography, multiple sleep latency test, possibly hypocretin determination in cerebrospinal fluid).
Non pharmacological therapy: a regular sleep wake rhythm, planned daytime naps, avoidance of shift work and alcohol support drug therapy.
Advantages over stimulants: pitolisant is not subject to narcotic regulations, has lower abuse potential and no known tolerance development. However, efficacy varies between individuals and some patients require additional or alternative classic stimulants.
You may also be interested in
- Modafinil, classic wake promoting agent in narcolepsy
- Methylphenidate, stimulant for narcolepsy and ADHD
- Dexamfetamine, stimulant as reserve therapy
- Sodium oxybate, GHB preparation for cataplexy
- Solriamfetol, additional wake promoting substance
Frequently Asked Questions
What is narcolepsy?
Narcolepsy is a rare, chronic neurological disorder characterised by pronounced daytime sleepiness, sudden sleep attacks, cataplexy (brief loss of muscle tone triggered by strong emotions), sleep paralysis and hypnagogic hallucinations. The cause is a deficiency of hypocretin (orexin) in the hypothalamus, often of autoimmune origin and described in some patient cohorts after the influenza A H1N1 pandemic of 2009.
What is the advantage of pitolisant over modafinil?
Pitolisant is not subject to narcotic regulations and has lower abuse potential than modafinil or classic stimulants. Efficacy on daytime sleepiness is comparable, and on cataplexy even superior. Pitolisant can also be used in patients without cataplexy. Selection depends on individual factors and tolerability.
How quickly does pitolisant work?
Initial improvements are often noticeable as early as the first week, full efficacy develops over 4 to 8 weeks of therapy with slow dose titration. In case of insufficient response after 2 months, switching to another substance or combination therapy may be considered.
Why does my pill no longer work under pitolisant?
Pitolisant induces the CYP3A4 enzyme, which metabolises the hormonal components of birth control pills. As a result, hormone levels drop and contraceptive safety can no longer be guaranteed. During therapy and for 21 days after discontinuation, additional or alternative non hormonal contraceptive methods (condom, copper IUD, sterilisation) should be used.
Sources
- EMA, Wakix (Pitolisant) EPAR
- DGSM Guideline on Narcolepsy
- Gelbe Liste, Pitolisant active substance profile
- BfArM, German Federal Institute for Drugs and Medical Devices
Legal Notices and Disclaimer
The information provided on this page is for general information purposes only and does not constitute medical advice, diagnosis or treatment recommendation. It does not replace the advice of a licensed physician or pharmacist. Medicines should always be taken only on medical prescription or pharmacy dispensing. All information is based on technical data sheets published at the time of preparation and recognised scientific sources; the manufacturer's current technical information always prevails. Sanoliste assumes no liability for the completeness, timeliness or accuracy of the information presented. In a medical emergency, call the emergency number 112.