PRIMIDONE

Mechanism of Action :

Primidone raises seizure thresholds and decreases excitability of neurons. It is partly metabolised to phenobarb which also exerts anticonvulsant activity.

Indication, Dosage and Frequency :


Oral
GENERALISED TONIC-CLONIC SEIZURES
Adult: Initially, 125 mg daily 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: 0.75-1.5 g daily.
Child: Initial dose: 125 mg daily, may increase by 125 mg every 3 days if needed. Maintenance: >9 yr: Same as adult dose; 6-9 yr: 0.75-1 g daily; 2-5 yr: 500-750 mg daily; <2 yr: 250-500 mg daily.
PARTIAL SEIZURES
Adult: Initially, 125 mg daily 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: 0.75-1.5 g daily.
Child: Initial dose: 125 mg daily, may increase by 125 mg every 3 days if needed. Maintenance: >9 yr: Same as adult dose; 6-9 yr: 0.75-1 g daily; 2-5 yr: 500-750 mg daily; <2 yr: 250-500 mg daily.
ESSENTIAL TREMOR
Adult: Initially, 50 mg daily gradually increased over 2-3 wk if necessary. Max dose: 750 mg daily.

Interactions :

Induces hepatic metabolism of many drugs; reduces efficacy of β-blockers, chloramphenicol, cimetidine, corticosteroids, furosemide, oral contraceptives, TCAs, warfarin. Increased plasma concentrations when used with valproate or phenytoin. Increased risk of osteomalacia when used with acetazolamide. May decrease serum levels of quinidine.