Apo-Primidone , Mysoline
Classifications: barbiturate; anticonvulsant; Therapeutic: anticonvulsant
Pregnancy Category: D
50 mg, 250 mg tablets; 250 mg/5 mL suspension
Converted in body to phenobarbital. Impairs vitamin D, calcium, folic acid, and vitamin B12 metabolism and utilization.
Antiepileptic properties result from raising the seizure threshold and changing seizure patterns.
Alone or concomitantly with other anticonvulsant agents in the prophylactic management of complex partial (psychomotor)
and generalized tonic-clonic (grand mal) seizures.
Hypersensitivity to barbiturates, porphyria; ethanol intoxication, hepatic encephalopathy, pregnancy (category D), lactation.
Chronic lung disease, sleep apnea; liver or kidney disease, dialysis; hyperactive children; mental status changes, major
depression, suicidal ideation.
Route & Dosage
Adult/Child (≥8 y): PO 250 mg/d, increased by 250 mg/wk (max: 2 g in 24 divided doses)
Child (<8 y): PO 125 mg/d, increased by 125 mg/wk (max: 2 g/d in 24 divided doses)
- Give whole or crush with fluid of patient's choice.
- Give with food if drug causes GI distress.
- Note: Transition from another anticonvulsant to primidone normally requires at least 21 wk.
Adverse Effects (≥1%)CNS: Drowsiness, sedation, vertigo, ataxia, headache,
excitement (children), confusion, unusual fatigue
, hyperirritability, emotional disturbances, acute psychoses (usually
patients with psychomotor epilepsy). Special Senses:
Diplopia, nystagmus, swelling of eyelids. GI: Nausea, vomiting, anorexia. Hematologic:
Leukopenia, thrombocytopenia, eosinophilia, decreased serum folate levels, megaloblastic anemia (rare). Skin:
Alopecia, maculopapular or morbilliform rash, edema, lupus erythematosus-like syndrome. Urogenital:
Impotence. Body as a Whole:
InteractionsDrug: Alcohol, cns depressants
compound CNS depression; phenobarbital
may decrease absorption and increase metabolism
of oral anticoagulants
; increases metabolism
, oral contraceptives
possibly decreasing their effects; antidepressants
potentiate adverse effects of primidone; griseofulvin
decreases absorption of primidone. Herbal: Kava, valerian
may potentiate sedation.
Approximately 6080% from GI tract. Peak:
4 h. Distribution:
Distributed into breast milk. Metabolism:
In liver to phenobarbital
and PEMA. Elimination:
In urine. Half-Life:
Primidone 324 h, PEMA 2448 h; phenobarbital
Assessment & Drug Effects
- Lab tests: Perform baseline and periodic CBC, complete blood chemistry (q6mo), and primidone blood levels. (Therapeutic
blood level for primidone: 510 mcg/mL.)
- Monitor primidone plasma levels (concentrations of primidone >10 mcg/mL are usually associated with significant ataxia and
- Therapeutic response may not be evident for several weeks.
- Observe for S&S of folic acid deficiency: Mental dysfunction, psychiatric disorders, neuropathy, megaloblastic anemia. Determine
serum folate levels if indicated.
- Be aware that presence of unusual drowsiness in breast fed newborns of primidone-treated mothers is an indication to discontinue
Patient & Family Education
- Avoid driving and other potentially hazardous activities during beginning of treatment because drowsiness, dizziness, and
ataxia may be severe. Symptoms tend to disappear with continued therapy; if they persist, dosage reduction or drug withdrawal
may be necessary.
- Avoid alcohol and other CNS depressants unless otherwise directed by physician.
- Do not take OTC medications unless approved by physician.
- Pregnant women should receive prophylactic vitamin K therapy for 1 mo prior to and during delivery to prevent neonatal hemorrhage.
- Withdraw primidone gradually to avoid precipitating status epilepticus.
- Carry medical information at all times. It needs to indicate medical diagnosis, medication(s), physician's name(s), address(es),
and telephone number(s).