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Indications and Usage

Primidone tablets used alone or concomitantly with other anticonvulsants, are indicated in the control of grand mal, psychomotor, and focal epileptic seizures. It may control grand mal seizures refractory to other anticonvulsant therapy.

Dosage and Administration

Usual Dosage

Patients 8 years of age and older who have received no previous treatment may be started on primidone tablets according to the following regimen using either 50 mg or scored 250 mg primidone tablets:

Days 1 to 3: 100 to 125 mg at bedtime.
Days 4 to 6: 100 to 125 mg twice a day.
Days 7 to 9: 100 to 125 mg three times a day.
Day 10 to maintenance: 250 mg three times a day.

For most adults and children 8 years of age and over, the usual maintenance dosage is three to four 250 mg primidone tablets in divided doses (250 mg three times a day or four times a day). If required, an increase to five or six 250 mg tablets daily may be made but daily doses should not exceed 500 mg four times a day.

Dosage should be individualized to provide maximum benefit. In some cases, serum blood level determinations of primidone may be necessary for optimal dosage adjustment. The clinically effective serum level for primidone is between 5 to 12 mcg/mL.

Patients Already Receiving Other Anticonvulsants

Primidone tablets should be started at 100 to 125 mg at bedtime and gradually increased to maintenance level as the other drug is gradually decreased. This regimen should be continued until satisfactory dosage level is achieved for the combination, or the other medication is completely withdrawn. When therapy with primidone tablets alone is the objective, the transition from concomitant therapy should not be completed in less than two weeks.

Pediatric Dosage

For children under 8 years of age, the following regimen may be used:

Days 1 to 3: 50 mg at bedtime.
Days 4 to 6: 50 mg twice a day.
Days 7 to 9: 100 mg twice a day.
Day 10 to maintenance: 125 mg three times a day to 250 mg three times a day.

For children under 8 years of age, the usual maintenance dosage is 125 mg to 250 mg three times daily or, 10 mg/kg/day to 25 mg/kg/day in divided doses.

Contraindications

Primidone is contraindicated in:

1) patients with porphyria and
2) patients who are hypersensitive to phenobarbital (see CLINICAL PHARMACOLOGY ).

Adverse Reactions

The most frequently occurring early side effects are ataxia and vertigo. These tend to disappear with continued therapy, or with reduction of initial dosage. Occasionally, the following have been reported: nausea, anorexia, vomiting, fatigue, hyperirritability, emotional disturbances, sexual impotency, diplopia, nystagmus, drowsiness, and morbilliform skin eruptions. Granulocytopenia, agranulocytosis, and red-cell hypoplasia and aplasia, have been reported rarely. These and, occasionally, other persistent or severe side effects may necessitate withdrawal of the drug. Megaloblastic anemia may occur as a rare idiosyncrasy to primidone and to other anticonvulsants. The anemia responds to folic acid without necessity of discontinuing medication.

To report SUSPECTED ADVERSE REACTIONS, contact Amneal Pharmaceuticals at 1-877-835-5472 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Description

Primidone, USP is a white, crystalline, highly stable substance, M.P. 279 to 284° C. It is poorly soluble in water (60 mg per 100 mL at 37°C) and in most organic solvents. It possesses no acidic properties, in contrast to its barbiturate analog.

Chemical name: 5-ethyldihydro-5-phenyl-4,6 (1H, 5H)-pyrimidinedione. Structural formula:

Primidone tablets USP, 50 mg and 250 mg, contain the following inactive ingredients: corn starch, lactose monohydrate, magnesium stearate, methyl cellulose, microcrystalline cellulose, sodium lauryl sulfate, sodium starch glycolate.

Clinical Pharmacology

Primidone raises electro- or chemoshock seizure thresholds or alters seizure patterns in experimental animals. The mechanism(s) of primidone's antiepileptic action is not known.

Primidone per se has anticonvulsant activity as do its two metabolites, phenobarbital and phenylethylmalonamide (PEMA). In addition to its anticonvulsant activity, PEMA potentiates the anticonvulsant activity of phenobarbital in experimental animals.

How Supplied / Storage and Handling

Primidone Tablets USP, 50 mg are supplied as white, round, flat-faced, bevel-edged tablet, debossed “AN” above “44” on one side and cut-bisected on the other side.

They are available as follows:

Bottles of 100:                         NDC 53746-544-01
Bottles of 500:                         NDC 53746-544-05
Bottles of 1000:                       NDC 53746-544-10

Primidone Tablets USP, 250 mg are supplied as white, round, flat-faced, bevel-edged tablet, debossed “AN” bisect “545” on one side and plain on the other side.

They are available as follows:

Bottles of 100:                         NDC 53746-545-01
Bottles of 500:                         NDC 53746-545-05
Bottles of 1000:                       NDC 53746-545-10

Store at 20° to 25°C (68° to 77°F); excursions permitted between 15° to 30°C (59° to 86°F)
[see USP Controlled Room Temperature].

Dispense contents with a child-resistant closure (as required) and in a tight, light-resistant container as defined in the USP.

KEEP THIS AND ALL MEDICATION OUT OF THE REACH OF CHILDREN.

Manufactured by:
Amneal Pharmaceuticals Pvt. Ltd.
Oral Solid Dosage Unit
Ahmedabad 382213, INDIA

Distributed by:
Amneal Pharmaceuticals LLC
Bridgewater, NJ 08807

Rev. 02-2022-05