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Primidone
Primidone (Mysoline)
Primidone
(PRIH-mih-dohn) Apo-Primidone Mysoline Sertan (Rx)

Classification: Anticonvulsant, miscellaneous

Action/Kinetics: Closely related to the barbiturates; however, the anticonvulsant mechanism is unknown. Produces a greater sedative effect than barbiturates when used for seizure treatment. Side effects usually subside with use. Peak plasma levels: 3 hr. Primidone is converted in the liver to two active metabolites, phenobarbital and phenylethylmalonamide (PEMA). Peak plasma levels (PEMA): 7-8 hr. t1/2 (primidone): 5-15 hr; t1/2 (PEMA): 10-18 hr; t1/2 (phenobarbital): 53-140 hr. The appearance of phenobarbital in the plasma may be delayed several days after initiation of therapy. Therapeutic plasma levels, primadone: 5-12 mcg/mL; phenobarbital, 15-40 mcg/mL. Primidone and metabolites are excreted through the kidneys, although 40% of primidone is excreted unchanged.

Uses: Alone or with other anticonvulsants to treat psychomotor seizures, focal seizures, or tonic-clonic seizures (including those refractory to barbiturate-hydantoin regimens). Investigational: Benign familial tremor.

Contraindications: Porphyria. Hypersensitivity to phenobarbital. Lactation.

Special Concerns: Safe use during pregnancy has not been determined. Use during lactation may result in drowsiness in the neonate. Children and geriatric clients may react to primidone with restlessness and excitement. Due to differences in bioavailability, brand interchange is not recommended.

Side Effects: CNS: Drowsiness, ataxia, vertigo, fatigue, hyperirritability, emotional disturbances, personality disturbances with mood changes and paranoia. GI: N&V;, anorexia, painful gums. Hematologic: Megaloblastic anemia, thrombocytopenia. Ophthalmologic: Diplopia, nystagmus. Miscellaneous: Impotence, morbilliform and maculopapular skin rashes. Occasionally has caused hyperexcitability, especially in children. Postpartum hemorrhage and hemorrhagic disease of the newborn. Symptoms of SLE.

Drug Interactions:
See also Barbiturates . Acetazolamide / Effect of primidone due to levels Carbamazepine / Plasma levels of primidone and phenobarbital and plasma levels of carbamazepine Hydantoins / Plasma levels of primidone, phenobarbital, and PEMA Isoniazid / Effect of primidone due to breakdown by liver Nicotinamide / Effect of primidone due to rate of clearance from body Succinimides / Plasma levels of primidone and phenobarbital

How Supplied: Suspension: 250 mg/5 mL; Tablet: 50 mg, 250 mg

Dosage
•Oral Suspension, Tablets Seizures, in clients on no other anticonvulsant medication.
Adults and children over 8 years, initial: Days 1-3, 100-125 mg at bedtime; days 4-6, 100-125 mg b.i.d.; days 7-9, 100-125 mg t.i.d.; maintenance: 250 mg t.i.d.-q.i.d. (may be increased to 250 mg 5-6 times/day; not to exceed 500 mg q.i.d.). Children under 8 years, initial: days 1-3, 50 mg at bedtime; days 4-6, 50 mg b.i.d.; days 7-9, 100 mg b.i.d.; maintenance: 125 mg b.i.d.-250 mg t.i.d. (10-25 mg/kg in divided doses).
Seizures, in clients receiving other anticonvulsants.
Initial: 100-125 mg at bedtime; then, increase to maintenance levels as other drug is slowly withdrawn (transition should take at least 2 weeks).
Benign familial tremor.
750 mg/day.