Drug reference

Primidone

Antiepileptic · Epilepsy and other seizure disorders

AntiepilepticEpilepsy and other seizure disorders

CDSCO approvedSchedule H

EXCRETION

—

not curated

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

Increased risk of teratogenicity. Monotherapy at the lowest effective dose is preferable if treatment must continue throughout pregnancy. Women of child-bearing potential should discuss with a specialist and use effective contraception.

FDA category + note

Top interactionssee all 12 →

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Mechanism

Primidone has intrinsic antiepileptic activity and is also metabolized to two active compounds: phenobarbital (via oxidation) and phenylethylmalonamide (PEMA, via ring scission). Evidence for primidone's own anticonvulsant effect includes its efficacy in newborns before phenobarbital has accumulated and in patients who do not respond to phenobarbital alone. During chronic therapy, plasma phenobarbital levels typically reach 2-3 times the primidone level, contributing significantly to the overall antiepileptic effect.

Indications

Simple partial seizuresComplex partial seizuresPartial with secondarily generalized tonic-clonic seizuresGeneralized tonic-clonic seizuresGTCSpartial epilepsy (as adjuvant to phenytoin or carbamazepine)

Dosing

Adult: Initially 125 mg at bedtime, increase by 125 mg every 3 days to 500 mg daily in 2 doses, then increase by 250 mg every 3 days. Maintenance: 0.75-1.5 g daily in 2 divided doses.
Pediatric: 10–20 mg/kg/day
Max dose: 1.5 g daily

Pharmacokinetics

Half-life

6–14 hours (primidone)

Metabolism

Primidone is partially converted to phenobarbitone and phenylethylmalonamide.

Excretion

About 1/3 excreted unchanged by kidney

Contraindications

Antiepileptic hypersensitivity syndrome

Side effects

Common

similar to phenobarbitone

Serious

Antiepileptic hypersensitivity syndrome (symptoms include fever, rash, lymphadenopathy, liver dysfunction, haematological, renal, and pulmonary abnormalities, vasculitis, and multi-organ failure)
Suicidal thoughts and behaviour
anaemia
leukopenia
psychotic reaction
lymph node enlargement (rarely)