Primidone
FDA Drug Information • Also known as: Mysoline, Primidone
- Brand Names
- Mysoline, Primidone
- Dosage Form
- POWDER
- Product Type
- BULK INGREDIENT
Description
DESCRIPTION Chemical name: 5-ethyldihydro- 5-phenyl-4,6 (1H, 5H) pyrimidinedione. Structural formula: C 12 H 14 N 2 O 2 M.W. 218.25 Primidone is a white crystalline powder, M.P. 279-284°C. It is very slightly soluble in methanol and methylene dichloride, slightly soluble in alcohol and insoluble in water. It possesses no acidic properties, in contrast to its barbiturate analog. Primidone tablets 50 mg and 250 mg contain the following inactive ingredients: lactose monohydrate, magnesium stearate, methyl cellulose, purified water, sodium lauryl sulphate, sodium starch glycolate and talc. Primidone tablets 250 mg also contain yellow iron oxide.
What Is Primidone Used For?
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
DOSAGE AND ADMINISTRATION Adult 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 b.i.d. Days 7 to 9: 100 to 125 mg t.i.d. Day 10 to maintenance: 250 mg t.i.d. 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. INITIAL:ADULTS AND CHILDREN OVER 8 KEY:
Side Effects (Adverse Reactions)
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 redcell 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.
Warnings and Precautions
WARNINGS The abrupt withdrawal of antiepileptic medication may precipitate status epilepticus. The therapeutic efficacy of a dosage regimen takes several weeks before it can be assessed. Suicidal Behavior and Ideation Antiepileptic drugs (AEDs), including primidone, increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior. Pooled analyses of 199 placebo-controlled clinical trials (mono- and adjunctive therapy) of 11 different AEDs showed that patients randomized to one of the AEDs had approximately twice the risk (adjusted Relative Risk 1.8, 95% CI:1.2, 2.7) of suicidal thinking or behavior compared to patients randomized to placebo. In these trials, which had a median treatment duration of 12 weeks, the estimated incidence rate of suicidal behavior or ideation among 27,863 AED-treated patients was 0.43%, compared to 0.24% among 16,029 placebo-treated patients, representing an increase of approximately one case of suicidal thinking or behavior for every 530 patients treated. There were four suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide. The increased risk of suicidal thoughts or behavior with AEDs was observed as early as one week after starting drug treatment with AEDs and persisted for the duration of treatment assessed. Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed. The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed. The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5 to 100 years) in the clinical trials analyzed. Table 1 shows absolute and relative risk by indication for all evaluated AEDs. Table 1 Risk by indication for antiepileptic drugs in the pooled analysis Indication Placebo Patientswith Events Per1000 Patients Drug Patientswith Events Per1000 Patients Relative Risk: Incidence of Events in Drug Patients/Incidence in Placebo Patients Risk Difference: Additional Drug Patients with Events Per 1000 Patients Epilepsy 1.0 3.4 3.5 2.4 Psychiatric 5.7 8.5 1.5 2.9 Other 1.0 1.8 1.9 0.9 Total 2.4 4.3 1.8 1.9 The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications. Anyone considering prescribing primidone or any other AED must balance the risk of suicidal thoughts or behavior with...
Contraindications
CONTRAINDICATIONS Primidone tablet is contraindicated in: 1) patients with porphyria and 2) patients who are hypersensitive to phenobarbital (see CLINICAL PHARMACOLOGY ).
How Supplied
HOW SUPPLIED Primidone tablets USP, 50 mg are white to off white, round, flat, beveled edged uncoated tablets debossed “RDY” and “477” on the periphery on one side and break line on other side. They are supplied in bottles of 30’s, 60’s, 100’s, 500’s and unit dose package of 100 (10 x 10). Bottles of 30 NDC 55111-477-30 Bottles of 60 NDC 55111-477-60 Bottles of 100 NDC 55111-477-01 Bottles of 500 NDC 55111-477-05 Unit Dosage Package of 100 (10 x 10) NDC 55111-477-78 Primidone tablets USP, 250 mg are cream to yellow, round, flat, beveled edged uncoated tablets debossed “RDY” and “476” on the periphery on one side and break line on other side. They are supplied in bottles of 30’s, 60’s, 100’s, 500’s and unit dose package of 100 (10 x 10). Bottles of 30 NDC 55111-476-30 Bottles of 60 NDC 55111-476-60 Bottles of 100 NDC 55111-476-01 Bottles of 500 NDC 55111-476-05 Unit Dosage Package of 100 (10 x 10) NDC 55111-476-78 Store at 20°–25° C (68°–77° F) [See USP Controlled Room Temperature]. Dispense in a well-closed container with a child-resistant closure. structure
About This Information
This drug information is sourced from FDA-approved labeling via the openFDA database. It is intended for educational and reference purposes only. This is not medical advice. Always consult your healthcare provider before making decisions about medication. Drug information may be updated by the FDA; check with your pharmacist for the most current information.
What are side effects?
Side effects are unwanted reactions that can occur when taking a medication. They range from mild (headache, nausea) to severe (allergic reactions, organ damage). Not everyone experiences side effects, and severity varies. Report any concerning side effects to your doctor.
What are drug interactions?
Drug interactions occur when a medication is affected by another drug, food, or supplement. Interactions can make medications less effective or cause dangerous side effects. Always tell your doctor about all medications and supplements you take.