Primidone


Concise Prescribing Info
Indications/Uses
Listed in Dosage.
Dosage/Direction for Use
Adult : PO Generalised tonic-clonic seizures; Partial seizures Initial: 125 mg at bedtime, increased by 125 mg every 3 days if needed up to 500 mg/day in 2 divided doses, may further increase by 250 mg every 3 days if needed. Maintenance: 750-1,500 mg/day. Essential tremor Initial: 50 mg/day, then increase over 2-3 wk if needed. Max: 750 mg/day.
Dosage Details
Oral
Essential tremor
Adult: Initially, 50 mg daily gradually increased over 2-3 wk if necessary. Max: 750 mg daily.

Oral
Generalised tonic-clonic seizures, Partial seizures
Adult: Initially, 125 mg at bedtime, increased by 125 mg every 3 days if necessary up to 500 mg daily given in 2 divided doses, may further increase by 250 mg every 3 days if needed. Maintenance: 750-1,500 mg daily given as 2 divided doses.
Child: Initially, 125 mg at bedtime, increased by 125 mg every 3 days if necessary up to maintenance daily doses given in 2 divided doses according to age. <2 yr 250-500 mg; 2-5 yr 500-750 mg; 6-9 yr 750-1,000 mg; >9 yr Same as adult dose.
Administration
May be taken with or without food. May be taken w/ food or milk to avoid stomach upset.
Contraindications
Acute porphyria.
Special Precautions
Patient w/ depression or suicidal tendency, hypoadrenalism, resp disease, history of drug abuse or potential for drug dependency. Avoid abrupt withdrawal. Hepatic and renal impairment. Childn. Pregnancy and lactation.
Adverse Reactions
Drowsiness, ataxia, vertigo, lethargy, anorexia, nausea, vomiting, headache, visual disturbances; hyperexcitability esp in childn including hyperirritability, fatigue, emotional disturbances, dizziness, diplopia, nystagmus, morbilliform rash, alopecia, oedema of eyelids or legs, leucopenia, eosinophilia, impotence, malignant lymphoma-like syndrome, syndrome resembling SLE. Rarely, acute psychosis-like reaction, red cell hypoplasia, megaloblastic anaemia, aplasia, granulocytopenia, agranulocytosis.
Patient Counseling Information
May impair ability to drive or operate machinery.
MonitoringParameters
Monitor CBC at 6-mth intervals. Monitor for signs of suicidal ideation and behaviours.
Overdosage
Symptoms: Crystalluria, ataxia, loss of consciousness, resp depression, coma. Management: General supportive treatment. Aspiration of stomach contents, admin of activated charcoal or IV fluids when necessary, forced alkaline diuresis.
Drug Interactions
Additive CNS depressant effect of opiates and barbiturates. Increased plasma levels w/ CYP3A4 inhibitors. Reduced plasma levels and/or shortened half-life of β-blockers, carbamazepine, ciclosporin, clozapine, chloramphenicol, corticosteroids/glucocorticosteroids, cyclophosphamide, dicoumarins, doxycycline, ethosuxamide, etoposide, felbamate, granisetron, lamotrigine, losartan, metronidazole, mianserin, nimodipine, OCs, oxcarbazepine, phenytoin, quinidine, rocuronium, Na valproate, tiagabine, theophyllines, topiramate, TCAs, vecuronium, warfarin, zonisamide.
Food Interaction
May potentiate CNS depressant effect of alcohol. Concomitant admin w/ St John’s wort may result in a reduction of plasma levels.
Action
Description: Primidone raises seizure threshold and decreases excitability of neurons. It is partially metabolised to phenobarbital which also exerts anticonvulsant activity.
Pharmacokinetics:
Absorption: Readily absorbed from the GI tract. Time to peak plasma concentration: Approx 3 hr.
Distribution: Widely distributed in all organs and tissues. Crosses the placenta and blood-brain barrier; enters breast milk. Volume of distribution: 0.6 L/kg. Plasma protein binding: 30%.
Metabolism: Undergoes hepatic metabolism, converted to phenobarbital via oxidation and to phenylethylmalonamide via scission of the heterocyclic ring.
Excretion: Via urine as unchanged drug (40%) and metabolites. Plasma half-life: 10-15 hr.
Chemical Structure

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Storage
Store below 25°C.
MIMS Class
ATC Classification
N03AA03 - primidone ; Belongs to the class of barbiturates and derivatives antiepileptics.
Disclaimer: This information is independently developed by MIMS based on Primidone from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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