Phenibut

INSTRUCTIONS FOR MEDICAL USE OF THE MEDICINAL PRODUCT PHENIBUT

Composition:

Active substance: phenibut (γ-amino-β-phenylbutyric acid hydrochloride);

1 tablet contains phenibut (γ-amino-β-phenylbutyric acid hydrochloride), recalculated to 100 % substance, 250 mg;

Excipients: lactose monohydrate, sodium carboxymethyl starch, colloidal anhydrous silicon dioxide, polyvinylpyrrolidone, calcium stearate.

Pharmaceutical form. Tablets.

Main physicochemical properties: round, flat-cylindrical tablets of white or white with a slightly yellowish tint color, with a bevel and a score line on one side.

Pharmacotherapeutic group. Other psychostimulants and nootropic agents.

ATC Code N06BX22.

Pharmacological Properties.

Pharmacodynamics.

Phenibut is a derivative of γ-aminobutyric acid (GABA) and phenylethylamine.

Its primary action is anti-hypoxic and anti-amnesic. Phenibut facilitates learning processes by improving memory and attention, and enhances both physical and mental performance. Psychological parameters (attention, memory, speed and accuracy of sensorimotor reactions) are improved under the influence of Phenibut. It has been established that Phenibut increases the neuron's energy potential by improving mitochondrial function.

Phenibut also possesses tranquilizing properties: it alleviates psychoemotional tension, anxiety, fear, emotional lability, irritability, improves sleep, and prolongs and enhances the effects of hypnotics, narcotics, neuroleptics, and anticonvulsants. Phenibut binds exclusively to GABA-ß receptors in the brain, thus exerting a moderate calming effect without causing undesirable sedative effects such as drowsiness, dizziness, reduced attention, or impaired performance. The drug prolongs the latent period and reduces the duration and intensity of nystagmus, exerting an antiepileptic effect. It does not affect cholinergic or adrenergic receptors.

Phenibut significantly reduces manifestations of asthenia and vasovegetative symptoms, including headache and a sensation of heaviness in the head. In patients with asthenia and emotionally labile individuals, Phenibut improves general well-being without causing excitation.

Pharmacokinetics.

Absorption and Distribution

The drug is well absorbed after oral administration and readily penetrates all body tissues, effectively crossing the blood-brain barrier (approximately 0.1% of the administered dose enters brain tissue, with notably greater penetration in both young and elderly individuals). The highest binding of phenibut occurs in the liver (80%), and this binding is non-specific.

Biotransformation and Excretion

80–95% of phenibut is metabolized in the liver; the metabolites are pharmacologically inactive.

Distribution in the liver and kidneys is close to uniform, while in the brain and blood it is lower than uniform. A significant amount of administered phenibut is detectable in urine within 3 hours. Simultaneously, the concentration of the drug in brain tissue does not decrease, and it remains detectable in the brain for up to 6 hours. On the following day, phenibut can only be detected in urine; it is also found in urine for up to 2 days after administration, but the amount detected constitutes only 5% of the administered dose. No accumulation is observed with repeated administration.

Clinical characteristics.

Indications.

Asthenic and anxiety-neurotic states (restlessness, fear, anxiety).

In children aged 8 to 14 years – stuttering, tics.

In elderly patients – insomnia, nocturnal restlessness.

Prophylaxis of stress conditions prior to surgery or painful diagnostic procedures.

Ménière’s disease, dizziness associated with vestibular dysfunction of various origins.

Prophylaxis of motion sickness (a specific condition characterized by nausea, vomiting, prostration, and vestibular dysfunction caused by being in a moving vehicle such as a ship or airplane).

As an adjunctive agent in the treatment of alcohol withdrawal syndrome.

Contraindications.

Hypersensitivity to the components of the drug. Acute renal failure.

Pregnancy and breastfeeding.

Interaction with other medicinal products and other forms of interaction.

Phenibut can be combined with psychotropic medicinal agents, reducing the doses of Phenibut and the concomitantly used medicinal agents.

Phenibut enhances and prolongs the effects of sedatives, narcotics, neuroleptics, and anti-parkinsonian drugs.

Special precautions for use

The drug should be used with caution in patients with gastric or intestinal disorders. To protect the mucosa from the irritating effect of phenibut, lower doses of the drug should be prescribed to these patients.

Blood parameters and liver function should be monitored during prolonged use.

The medicinal product contains lactose and therefore should not be used in patients with rare hereditary forms of galactose intolerance, lactase deficiency, or glucose-galactose malabsorption syndrome.

Use during pregnancy or breastfeeding

In animal studies, no mutagenic, teratogenic, or embryotoxic effects of phenibut have been observed. There are no adequate and well-controlled studies on the safety of phenibut use in pregnant women. Therefore, the use of Phenibut during pregnancy or breastfeeding is contraindicated.

Ability to influence reaction rate while driving or operating machinery

Patients who experience drowsiness, dizziness, or other central nervous system disturbances during treatment with the drug should refrain from driving or operating machinery.

Method of Administration and Dosage.

Phenibut is taken orally before meals. The tablet should be swallowed whole, with sufficient amount of water.

For asthenic and anxiety-neurotic conditions in adults: 250–500 mg (1–2 tablets) three times daily. Maximum single doses: for adults – 750 mg; for elderly patients – 500 mg.

The treatment course lasts 2–3 weeks. If necessary, the course may be extended to 4–6 weeks.

For children aged 8 to 14 years: 250 mg (1 tablet) three times daily. The treatment course lasts 2–6 weeks.

For vestibular apparatus dysfunction of infectious origin and for Meniere's disease during exacerbation: Phenibut is administered at 750 mg (3 tablets) three times daily for 5–7 days; when vestibular disturbances subside – 250–500 mg (1–2 tablets) three times daily for 5–7 days, followed by 250 mg (1 tablet) once daily for 5 days. In cases of relatively mild disease course, Phenibut is administered at 250 mg (1 tablet) twice daily for 5–7 days, then 250 mg once daily for 7–10 days.

For relief of vertigo in vascular and traumatic vestibular dysfunction: Phenibut is administered at 250 mg three times daily for 12 days.

For prevention of motion sickness: the drug is administered at a dose of 250–500 mg as a single dose one hour before the expected onset of motion or upon appearance of the first symptoms of motion discomfort.

For management of alcohol withdrawal syndrome: during the first days of treatment, 250–500 mg of Phenibut is administered three times daily and 750 mg at bedtime, with gradual reduction of the daily dose to the usual adult dose.

Patients with hepatic impairment.

In patients with hepatic impairment, high doses of the drug may cause hepatotoxicity; therefore, lower doses are prescribed for this patient group.

Patients with renal impairment.

There are no data indicating adverse effects of Phenibut in patients with impaired renal function when administered at therapeutic doses.

No drug dependence or withdrawal syndrome has been observed during Phenibut use.

Literature sources have reported isolated cases of tolerance to Phenibut.

Children.

The medicinal product can be prescribed to children aged 8 years and older.

Overdose.

Phenibut is a low-toxic medicinal product. It may become hepatotoxic only when administered at daily doses of 7–14 g over a prolonged period. Data on overdose are lacking.

The indicated doses significantly exceed the recommended dose (average therapeutic dose is 500–2000 mg).

Symptoms: drowsiness, nausea, vomiting, dizziness.

With prolonged use of high doses, arterial hypotension, acute renal failure, eosinophilia, and fatty liver degeneration may develop.

Treatment: gastric lavage. Symptomatic therapy.

There is no specific antidote.

Adverse Reactions

Phenibut, like other medicinal products, may cause adverse reactions, although they do not occur in all patients.

Classification of adverse reactions by frequency: 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); frequency not known (cannot be estimated from available data).

Nervous system disorders: frequency not known – drowsiness (at the beginning of treatment), headache and dizziness (at doses above 2 g per day; reducing the dose decreases the intensity of this adverse effect).

Gastrointestinal disorders: frequency not known – nausea (at the beginning of treatment), vomiting, diarrhea, epigastric pain.

Hepatobiliary disorders: frequency not known – hepatotoxicity (with prolonged use of high doses).

Immune system disorders: frequency not known – hypersensitivity reactions, including urticaria, erythema, rash, angioneurotic edema, facial swelling, tongue swelling.

Skin and subcutaneous tissue disorders: rare – allergic reactions (rash, itching).

Psychiatric disorders: frequency not known – emotional lability, sleep disturbances (these adverse reactions may occur in children if instructions for use are not followed).

If adverse reactions not listed in this instruction occur during treatment, or if any of the listed adverse reactions are particularly severe, please consult your physician.

Shelf life. 3 years.

Do not use the medicinal product after the expiry date.

Storage conditions.

Store in the original packaging at a temperature not exceeding 25 °C.

Keep out of reach and sight of children.

Packaging.

Tablets of 250 mg in blisters of 10 (10×1) or 20 (10×2) or 30 (10×3) or 50 (10×5) in cardboard packs.

Prescription status.

Prescription only.

Manufacturer.

JSC "Monfarm", Ukraine.

Manufacturer's address and place of business.

8, Zavodska Street, Avramivka, Uman district, Cherkasy region, 19161, Ukraine.