III. Contraindications

  1. Porphyria
  2. Phenobarbital Hypersensitivity

IV. Mechanism

  1. Barbiturate with 2 active metabolites
    1. Phenobarbital
    2. Phenylethylmalonamide (PEMA)
  2. Raises Seizure threshold

V. Dosing: adults and children over age 8 years

  1. Titration to maintenance dose
    1. Days 1 to 3: Take 100-125 mg PO qhs
    2. Days 4 to 6: Take 100-125 mg PO bid
    3. Days 7 to 9: Take 100-125 mg PO tid
    4. Days >10: Take 250 mg PO tid
  2. Maintenance dosing
    1. Standard dosing: 250 mg PO tid-qid
    2. Maximum dosing: 500 mg PO qid (do not exceed)

VI. Monitoring: Labs every 6 months

  1. Complete Blood Count
  2. Chemistry panel (SMA-12)

VII. Adverse effects

  1. Common
    1. Ataxia
    2. Vertigo
  2. Occasional
    1. Nausea, Vomiting or Anorexia
    2. Fatigue or drowsiness
    3. Hyperirritability or other emotional disturbance
    4. Sexual Impotence
    5. Diplopia or Nystagmus
    6. Morbilliform skin rash
  3. Rare
    1. Megaloblastic Anemia responsive to Folate

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Related Studies

Cost: Medications

primidone (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
PRIMIDONE 250 MG TABLET Generic $0.29 each
PRIMIDONE 50 MG TABLET Generic $0.15 each