Drug information of Primidone

Primidone

Drug group: Anticonvulsants

Primidone is used alone or in combination with other medicines, to control seizures (convulsions) in the treatment of epilepsy . This medicine is an anticonvulsant that works in the brain tissue to stop seizures.

Mechanism of effect

Primidone is a GABA receptor agonist. The mechanism of Primidone's antiepileptic action is not known. It is believed to work via interactions with voltage-gated sodium channels which inhibit high-frequency repetitive firing of action potentials. The major metabolite, phenobarbital, is also a potent anticonvulsant in its own right and likely contributes to primidone's effects in many forms of epilepsy.

Pharmacodynamic

Primidone is a barbiturate with anticonvulsant properties. Primidone, either alone or used concomitantly with other anticonvulsants, is indicated in the control of grand mal, psychomotor, and focal epileptic seizures.
It may control grand mal seizures refractory to other anticonvulsant therapy. Primidone raises electro- or chemoshock seizure thresholds or alters seizure patterns in experimental animals. Primidone has anticonvulsant activity as do its two metabolites, phenobarbital and phenylethylmalonamide (PEMA).

Pharmacokinetics

Primidone is well absorbed. Its metabolism is hepatic to phenobarbital (active) and to phenylethylmalonamide.
Excretion is through urine (15% to 65% as unchanged drug; the remainder is unconjugated PEMA, phenobarbital and its metabolites).
Half-Life Elimination varies: Primidone: 5 to16 hours (variable); PEMA: 16 to 50 hours (variable); Phenobarbital: 50 to 150 hours).

Drug indications

Anticonvulsant

Dosage

Adults
Usual Adult Dose for seizures:
Days 1 to 3: 100 to 125 mg orally at bedtime
Days 4 to 6: 100 to 125 mg orally twice a day
Days 7 to 9: 100 to 125 mg orally three times a day
Day 10 onward: 250 mg orally three to four times a day, increasing up to five or six times a day if necessary, not to exceed 500 mg four times a day (2 g/day).
Pediatrics
Usual Pediatric Dose for seizures:
Neonates:
12 to 20 mg/kg/day in 2 to 4 divided doses, beginning with lower dosage and titrating upward
Children:
Less than 8 years:
Initial dose: 50 to 125 mg/day given at bedtime and increased by increments of 50 to 125 mg/day every 3 to 7 days
Maintenance dose: 10 to 25 mg/kg/day in 3 to 4 divided doses
Greater than or equal to 8 years:
• Initial dose: 125 to 250 mg/day at bedtime and increased by increments of 125 to 250 mg/day every 3 to 7 days
• Maintenance dose: 750 to 1500 mg/day in 3 to 4 divided doses
• Maximum dose: 2 g/day

Drug contraindications

Pregnancy , patients with porphyria

Alerts

• you should not use this medication if you are allergic to primidone or phenobarbital or if you have porphyria.
• Before taking this medication, tell your doctor if you are allergic to any drugs, or if you are pregnant or breast-feeding.
• If you are taking primidone to prevent seizures, keep taking the medication even if you feel fine. You may have an increase in seizures if you stop taking primidone.

Points of recommendation

• Take this medication exactly as it was prescribed for you.
• Do not take the medication in larger amounts.
Primidone is usually taken 2 to 4 times daily.
• If you are switching to primidone from another seizure medication, you may need to start taking primidone only at bedtime.

Pregnancy level

D


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