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Pharmacologic class: Barbiturate
Therapeutic class: Anticonvulsant
Pregnancy risk category NR
Unknown. May raise seizure threshold by decreasing neuronal firing after being converted to phenobarbital.
Suspension: 250 mg/5 ml
Tablets: 50 mg, 250 mg
Indications and dosages
➣ Grand mal, psychomotor, or focal epileptic seizures
Adults and children ages 8 and older: Initially, 100 to 125 mg P.O. at bedtime on days 1 to 3, then 100 to 125 mg P.O. b.i.d. on days 4 to 6, then 100 to 125 mg P.O. t.i.d. on days 7 to 9, followed by a maintenance dosage of 250 mg P.O. three or four times daily
Children younger than age 8: Initially, 50 mg P.O. at bedtime on days 1 to 3, then 50 mg P.O. b.i.d. on days 4 to 6, then 100 mg P.O. b.i.d. on days 7 to 9. For maintenance, 125 to 250 mg t.i.d. or 10 to 25 mg/kg/day in divided doses.
• Renal impairment
• Benign familial (essential) tremor
• Hypersensitivity to drug or phenobarbital
Use cautiously in:
• hepatic, renal, or chronic obstructive pulmonary disease
• pregnant or breastfeeding patients
• hyperactive children.
• Don't change brands. Bioequivalency problems have occurred.
☞ Don't stop therapy suddenly. Dosage must be tapered.
• Know that drug may be given alone or with other anticonvulsants.
CNS: headache, dizziness, stimulation, drowsiness, sedation, confusion, hallucinations, psychosis, ataxia, vertigo, hyperirritability, emotional disturbances, paranoid symptoms, coma
EENT: diplopia, nystagmus, eyelid edema
GI: nausea, vomiting, anorexia
GU: erectile dysfunction
Hematologic: megaloblastic anemia,
Skin: flushing, rash
Drug-drug. Acetazolamide, succinimide: decreased primidone blood level Carbamazepine: decreased primidone blood level, increased carbamazepine blood level
Hydantoins, isoniazid, nicotinamide: increased primidone blood level
Drug-diagnostic tests. Hemoglobin, platelets: decreased levels
Liver function tests: altered results
• Monitor primidone and phenobarbital blood levels.
• Monitor CBC and blood chemistry. Watch for evidence of blood dyscrasias.
• Assess neurologic status regularly. Stay alert for excessive drowsiness and emotional status changes.
☞ Caution patient not to discontinue therapy suddenly. Advise him to discuss dosage changes with prescriber.
☞ Instruct patient to immediately report unusual bleeding, bruising, or rash.
• Tell patient drug may cause sexual dysfunction. Advise him to discuss this issue with prescriber.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, vision, and alertness.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.