Primidone (Tablets) Instructions for Use

Marketing Authorization Holder

Akrikhin Chemical and Pharmaceutical Plant, JSC (Russia)

ATC Code

N03AA03 (Primidone)

Active Substance

Primidone (Rec.INN registered by WHO)

Dosage Form

Primidone

Tablets 250 mg: 10, 20, 30, 40, or 50 pcs.

Dosage Form, Packaging, and Composition

Tablets are white, flat-cylindrical in shape, with a bevel and a score line.

Excipients: potato starch – 110 mg, sodium carboxymethyl starch (sodium starch glycolate) – 16 mg, povidone – 20 mg, calcium stearate – 4 mg.

10 pcs. – contour cell blisters (1) – cardboard packs.
10 pcs. – contour cell blisters (2) – cardboard packs.
10 pcs. – contour cell blisters (3) – cardboard packs.
10 pcs. – contour cell blisters (4) – cardboard packs.
10 pcs. – contour cell blisters (5) – cardboard packs.

Clinical-Pharmacological Group

Anticonvulsant drug

Pharmacotherapeutic Group

Antiepileptic agent

Pharmacological Action

Anticonvulsant agent, belongs to barbiturates. Reduces the excitability of neurons in the epileptogenic focus. Causes a mild hypnotic effect.

Pharmacokinetics

After oral administration, it is rapidly and completely absorbed from the gastrointestinal tract. Bioavailability is more than 90%. T_max is achieved after 3 hours. V_d is 0.64-0.86 L/kg. Primidone is metabolized in the liver to form 2 active metabolites: phenobarbital – 15-25% and phenylethylmalonamide. Plasma protein binding of primidone is 20%, phenobarbital is 50%, phenylethylmalonamide is negligible. T_1/2 of primidone, phenobarbital, and phenylethylmalonamide is 3-23, 75-126, and 10-25 hours, respectively. It is excreted by the kidneys as primidone – 64%, phenobarbital – 5.1%, phenylethylmalonamide – 6.6%.

Primidone and its metabolites are excreted in breast milk, where their average concentration is 75% of the C_ss in blood.

Indications

Epilepsy of various origins, manifested primarily by major convulsive seizures. Less effective for focal, myoclonic, and akinetic seizures.

ICD codes

Dosage Regimen

Initiate treatment with a single dose of 125 mg taken orally once daily after a meal.

Increase the daily dose by 250 mg for adults every three days.

Increase the daily dose by 125 mg for children under nine years of age every three days.

Titrate the dose gradually until the desired therapeutic effect is achieved.

Administer the total daily dose in two divided doses for maintenance therapy.

Do not exceed the maximum daily dose of 1.5 g for adult patients.

Do not exceed the maximum daily dose of 1 g for pediatric patients.

Adjust the dosage regimen individually based on clinical response and tolerability.

Monitor plasma concentrations of primidone and its metabolites to guide dosing.

Discontinue therapy gradually; avoid abrupt withdrawal to prevent status epilepticus.

Adverse Reactions

From the central nervous system: drowsiness, apathy, anxiety, headache, dizziness may occur; rarely – nystagmus, ataxia, psychotic reactions.

From the digestive system: nausea, vomiting may occur.

From the hematopoietic system: rarely – leukopenia, lymphocytosis; in some cases – megaloblastic anemia.

Other: allergic reactions may occur; rarely – lupus-like syndrome, arthralgia.

Contraindications

Diseases of the liver, kidneys, and hematopoietic system; pregnancy, lactation; hypersensitivity to primidone.

Use in Pregnancy and Lactation

Contraindicated for use during pregnancy and during the lactation (breastfeeding) period.

Use in Hepatic Impairment

Contraindicated in liver diseases.

Use in Renal Impairment

Contraindicated in kidney diseases.

Pediatric Use

Use with caution in children.

Geriatric Use

Use with caution in elderly patients. With long-term use, drug dependence may develop.

Special Precautions

Discontinuation of therapy and replacement of primidone should be done gradually.

Use with caution in elderly and debilitated patients. With long-term use, drug dependence may develop.

In case of megaloblastic anemia development, Primidone should be discontinued and treatment with folic acid and/or vitamin B₁₂ should be initiated.

Use with caution in children.

Effect on ability to drive vehicles and operate machinery

Primidone causes a decrease in the speed of psychomotor reactions, therefore, during the treatment period, driving vehicles, working with machinery, and other potentially hazardous activities should be avoided.

Drug Interactions

With simultaneous use with acetazolamide, osteomalacia, rickets, and a decrease in the effectiveness of primidone are possible.

There are reports of an increase, decrease, and no change in the plasma concentration of primidone when used simultaneously with valproic acid.

With simultaneous use with clonazepam, the plasma concentration of primidone increases; with phenobarbital – an increase in the plasma concentration of phenobarbital is possible.

Storage Conditions

Store at 2°C (36°F) to 25°C (77°F). Keep in original packaging, protected from light. Keep out of reach of children.

Dispensing Status

Rx Only

Important Safety Information

This information is for educational purposes only and does not replace professional medical advice. Always consult your doctor before use. Dosage and side effects may vary. Use only as prescribed.