Primidone

A to Z Drug Facts

(PRIM-ih-dohn)

Mysoline,  Apo-Primidone, Sertan

Class: Anticonvulsant

 Action Drug and its metabolites (phenobarbital and phenylethylmalonamide) have anticonvulsant activity, raising seizure threshold and altering seizure patterns.

 Indications Control of grand mal, psychomotor or focal epileptic seizures; may control grand mal seizures refractory to other anticonvulsants. Unlabeled use(s): Treatment of benign familial tremor (essential tremor).

 Contraindications Hypersensitivity to barbiturates; porphyria.

 Route/Dosage

ADULTS & CHILDREN > 8 YR: If no previous treatment, initiate as follows: PO Days 1 to 3: 100 to 125 mg at bedtime; days 4 to 6: 100 to 125 mg bid; days 7 to 9: 100 to 125 mg tid; day 10 through maintenance: 250 mg tid or qid. May increase to 250 mg 5 to 6 times/day, but do not exceed 500 mg qid (2 g/day). CHILDREN < 8 YR: PO Days 1 to 3: 50 mg at bedtime; days 4 to 6: 50 mg bid; days 7 to 9: 100 mg bid; day 10 through maintenance: 125 to 250 mg tid or 10 to 25 mg/kg/day in divided doses.

Patients Already Taking Anticonvulsants

Initiate at 100 to 125 mg at bedtime, gradually increasing dose to maintenance level as other drug is gradually decreased. Complete switch to primidone should occur over > 2 wk.

 Interactions

Anticoagulants: Decreased anticoagulant effects. Beta-blockers: Decreased bioavailability of beta-blockers. Carbamazepine: Decreased primidone levels; increased concentrations of carbamazepine. Corticosteroids: Decreased effect of corticosteroids. Doxycycline: Decreased doxycycline serum levels. Estrogens, oral contraceptives: Contraceptive failure. Ethanol: Additive CNS suppression. Felodipine: Decreased effect of felodipine. Griseofulvin: Decreased serum griseofulvin levels. Hydantoins, valproic acid: Increased primidone serum levels. Methoxyflurane: Enhanced renal toxicity. Metronidazole: Therapeutic failure of metronidazole. Nifedipine: Decreased nifedipine levels. Phenylbutazone, oxyphenbutazone: Shortened elimination rate of these agents. Quinidine: Decreased quinidine serum levels. Succinimides: Decreased primidone levels. Theophyllines: Decreased theophylline levels.

 Lab Test Interferences None well documented.

 Adverse Reactions

CNS: Ataxia; vertigo; fatigue; hyperirritability; emotional disturbances; drowsiness; personality deterioration; mood changes; paranoia. DERM: Morbilliform or maculopapular skin eruptions. EENT: Diplopia; nystagmus. GI: Nausea; anorexia; vomiting. GU: Impotence; crystalluria. HEMA: Megaloblastic anemia; thrombocytopenia.

 Precautions

Pregnancy: Pregnancy category undetermined. Consult physician regarding anticonvulsant use during pregnancy. Lactation: Excreted in breast milk. Status epilepticus: May be precipitated by abrupt withdrawal.

 Administration/Storage

• Administer in divided doses.
• For patients with swallowing difficulties, crush tablets or use suspension.
• Do not reach maximum dose in < 10 days (maximum adult dose: 2 g day; maximum pediatric dose: 25 mg/kg/day).
• Do not substitute one brand of drug for another; bioequivalence problems exist.
• Shake suspension well, do not freeze.
• Store at room temperature in tightly-closed, light-resistant container.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Note liver disease, renal disease, or porphyria.
• Ensure that complete blood cell count and sequential multiple analyzer 12 tests have been obtained before beginning therapy; repeat q 6 mo throughout treatment.
• Monitor drug blood level (5 to 12 mcg/ml) periodically during therapy.
• Observe for common side effects such as ataxia, vertigo, or somnolence; notify physician if these symptoms occur.

 Patient/Family Education

• Instruct patient to take with food if GI distress occurs.
• Explain that full effectiveness of drug may not occur for several weeks after initiation of drug therapy.
• Warn the patient that discontinuing medication too quickly may precipitate status epilepticus; explain that dosage will be tapered slowly before stopping.
• Advise patient to notify physician or dentist of medication regimen before treatment or surgery.
• Instruct patient to report the following symptoms to physician: Ataxia, vertigo, drowsiness, nausea, vomiting or loss of appetite. Advise patient that ataxia or vertigo are common side effects, but usually resolve with continued therapy.
• Caution patient to avoid intake of alcoholic beverages, other CNS depressants or otc medications unless authorized by physician.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts