Adult: Initially, 50 mg daily, may increase gradually over 2-3 weeks based on patient’s clinical response and tolerability. Max: 750 mg daily. Dosing recommendations may vary among countries or individual products or preparations. Refer to country- or product-specific recommendations. Elderly: Dosage reduction may be required.
Oral Grand mal epilepsy, Partial seizures, Psychomotor epilepsy
Adult: Dose is individualised based on patient’s clinical response and tolerability. As monotherapy or in combination with other anticonvulsants: Initially, 125 mg once daily at bedtime, may increase by 125 mg every 3 days up to a total of 500 mg daily in 2 divided doses. If needed, may further increase by 250 mg every 3 days. Maintenance: 750-1,500 mg daily to be given in 2 divided doses. Max: 1,500 mg daily. In patients on other anticonvulsants, initiating primidone and withdrawal of previous treatment should be gradually done over a period of 2 weeks. Dosing recommendations may vary among countries or individual products or preparations. Refer to country- or product-specific recommendations. Elderly: Dosage reduction may be required. Child: Dose is individualised based on patient’s clinical response and tolerability. Initially, 125 mg once daily at bedtime, may increase by 125 mg every 3 days. Maintenance: <2 years 250-500 mg daily; 2-5 years 500-750 mg daily; 6-9 years 750-1,000 mg daily; >9 years Same as adult dose. Maintenance doses are to be given in 2 divided doses. Dosing recommendations may vary among countries or individual products or preparations. Refer to country- or product-specific recommendations.
Special Patient Group
Debilitated patients: Dosage reduction may be required.
Dosage reduction may be required.
Dosage reduction may be required.
May be taken with or without food. May be taken w/ food or milk to avoid stomach upset.
Acute intermittent porphyria.
Patients with depression, suicidal tendencies, history of drug abuse or potential for drug dependency, hypoadrenalism, respiratory disease. Debilitated patients. Avoid abrupt withdrawal. Children and elderly. Renal and hepatic impairment. Pregnancy and lactation.
Significant: Suicidal ideation and behaviour; rarely, megaloblastic anaemia and blood dyscrasias; decreased serum folate and vitamin D levels (long-term therapy). Eye disorders: Visual disturbances, diplopia. Gastrointestinal disorders: Nausea, vomiting. General disorders and administration site conditions: Fatigue. Immune system disorders: Rarely, exfoliative dermatitis, SLE. Metabolism and nutrition disorders: Anorexia. Musculoskeletal and connective tissue disorders: Arthralgia, Dupuytren’s contracture, osteomalacia. Nervous system disorders: Drowsiness, headache, dizziness, nystagmus, ataxia, vertigo. Psychiatric disorders: Apathy, listlessness, personality change, hyperirritability. Reproductive system and breast disorders: Sexual impotency. Skin and subcutaneous tissue disorders: Maculopapular, morbilliform or scarlatiniform rashes. Potentially Fatal: Rarely, Stevens-Johnson syndrome, toxic epidermal necrolysis.
PO: Z (Insufficient data to conclude its safety and risk during pregnancy. Use only when benefits outweigh risks.)
Patient Counseling Information
This drug may cause drowsiness or reduced alertness, if affected, do not drive or operate machinery. Women of childbearing potential must use proven birth control methods during therapy and for 2 months after stopping the treatment. Consider using other reliable contraceptive methods recommended by the doctor as hormonal contraceptives may be ineffective.
Pregnancy test may be considered in women of childbearing potential to rule out pregnancy before initiating treatment. Monitor serum primidone and phenobarbital levels, CBC; signs of depression, suicidal ideation and behaviours, neurological status; serum folate levels; bone density (long-term therapy). Obtain comprehensive metabolic panel at 6-month intervals to compare with baseline at the start of therapy.
Symptoms: CNS depression (e.g. ataxia, loss of consciousness, respiratory depression, coma), crystalluria. Management: General supportive treatment. May perform aspiration of stomach contents, administer activated charcoal or IV fluids, forced alkaline diuresis depending on the severity of intoxication. May perform haemoperfusion (if the patient is hypotensive) or haemodialysis in a more life-threatening situation.
May have increased serum concentration with CYP3A4 inhibitors (e.g. chloramphenicol, felbamate, nelfinavir, metronidazole, Na valproate). May increase metabolism resulting in lower serum concentration and shorter half-life of androgens, β-antagonists, carbamazepine, chloramphenicol, clozapine, corticosteroids, cyclophosphamide, cyclosporin, dicoumarins, digitoxin, doxycycline, ethosuximide, etoposide, felbamate, granisetron, lamotrigine, losartan, methadone, metronidazole, mianserin, montelukast, nelfinavir, nimodipine, oral contraceptives, oxcarbazepine, phenytoin, quinidine, rocuronium, Na valproate, tiagabine, theophylline, topiramate, TCAs, vecuronium, warfarin, zonisamide. May increase the hepatotoxicity of paracetamol. Additive CNS depressant effect with other CNS depressant (e.g. barbiturates, opiates).
May have decreased serum concentration with St. John’s wort. Additive CNS depressant effect with alcohol. May have increased duration of action with protein-deficient diets.
Description: Mechanism of Action: Primidone raises the seizure threshold and decreases the excitability of neurons. It is metabolised into 2 active metabolites namely, phenobarbital and phenylethylmalonamide (PEMA) where PEMA potentiates the activity of phenobarbital. Pharmacokinetics: Absorption: Rapidly absorbed from the gastrointestinal tract. Bioavailability: >90%. Time to peak plasma concentration: 0.5-9 hours (variable). Distribution: Well distributed in all organs and tissues. Crosses the placenta, enters breast milk and crosses the blood-brain barrier. Volume of distribution: 0.6-0.75 L/kg. Plasma protein binding: <20%. Metabolism: Metabolised in the liver via oxidation into phenobarbital and via ring cleavage at the 2nd carbon position into phenylethylmalonamide (PEMA). Excretion: Via urine (15-65% as unchanged drug; remainder is metabolites). Elimination half-life: Approx 10-15 hours.
Store below 25°C. Protect from light and moisture.