Professional Information — Primidone

Indications and Usage

Primidone, used alone or 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.

Dosage and Administration

Usual Dosage

Patients 8 years of age and older who have received no previous treatment may be started on primidone 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 t.i.d. or q.i.d.). If required, an increase to five or six 250 mg tablets daily may be made but daily doses should not exceed 500 mg q.i.d.

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 µg/mL.

Patients Already Receiving Other Anticonvulsants

Primidone 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be continued until satisfactory dosage level is achieved for the combination, or the other medication is completely withdrawn.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 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 to 250 mg three times daily or, 10 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 ACTIONS ).

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 Oxford Pharmaceuticals, LLC at 1-844-508-1455, 8:00 AM to 4.30 PM ET, Monday – Friday or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Description

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

Primidone is a white, crystalline, highly stable substance, M.P. 279-284°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.

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

Primidone 250 mg tablets also contain D&C yellow #10 aluminum lake and FD&C yellow #5 aluminum lake.

How Supplied / Storage and Handling

Primidone 50 mg Tablets, USP are white, round, flat faced, beveled edge, scored tablets debossed "684" above bisect on one side and "O" on the other side. Supplied in:
Bottles of 30, NDC 72789-178-30

Primidone 250 mg Tablets, USP are yellow, round, flat faced, beveled edge, scored tablets debossed "685" above bisect on one side and "O" on the other side. Supplied in:

Bottles of 30, NDC 72789-177-30

Storage
Store at 20° to 25°C (68° to 77°F) [See USP Controlled Room Temperature].

Dispense in a tight, light-resistant container with a child-resistant closure.

Dispense with Medication Guide available at:https://www.oxford-rx.com/med-guides

Patient Counseling Information

Suicidal Thinking and Behavior- Patients, their caregivers, and families should be counseled that AEDs, including primidone, may increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self- harm. Behaviors of concern should be reported immediately to healthcare providers.

Pregnancy- Patients should be encouraged to enroll in the NAAED Pregnancy Registry if they become pregnant. This registry is collecting information about the safety of antiepileptic drugs during pregnancy. To enroll, patients can call the toll free number 1-888-233-2334 (see WARNINGS, Pregnancy  section).

Please refer to the Primidone Tablets, USP Medication Guide provided with the product for more information.