• See Also
  1. Seizure Disorder
  2. Essential Tremor
  • Indications
  1. Essential Tremor
  2. Seizure Disorder
    1. Generalized Tonic Clonic Seizures (Grand Mal Seizure)
    2. Psychomotor Seizure
    3. Focal Seizure
  • Contraindications
  1. Porphyria
  2. Phenobarbital Hypersensitivity
  • Mechanism
  1. Barbiturate with 2 active metabolites
    1. Phenobarbital
    2. Phenylethylmalonamide (PEMA)
  2. Raises Seizure threshold
  1. Start 12.5 mg to 25 mg orally at bedtime
  2. Titrate weekly by 50 mg/day, up to 250 mg/day divided once to twice daily
  3. Maximum: 750 mg/day
  • Dosing
  • Seizures - Adults and Children (over age 8 years)
  1. Titration to maintenance dose (over first 10 days)
    1. Days 1 to 3: Take 100 to 125 mg orally at bedtime
    2. Days 4 to 6: Take 100 to 125 mg orally twice daily
    3. Days 7 to 9: Take 100 to 125 mg orally three times daily
    4. Days >10: Take 250 mg orally three times daily
  2. Maintenance dosing
    1. Standard dosing: 250 mg orally three to four times daily
    2. Maximum dosing: 500 mg orally four time daily (do not exceed)
  • Dosing
  • Seizures - Children (under age 8 years)
  1. Start 50 mg orally at bedtime
  2. TItrate dose over 10 days (similar stepped titration schedule as for adults)
    1. Typical: 125 to 250 mg orally three times daily (10 to 25 mg/kg/day in divided doses)
  • Monitoring
  • Labs every 6 months
  1. Complete Blood Count
  2. Chemistry panel (SMA-12)
  • 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
  • Safety
  1. Pregnancy Category D
  2. Avoid in Lactation
  • Resources
  1. Primidone (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=ae0fa704-818e-4423-8e3a-6cc3390cdd7d
  • References
  1. Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 56-7
  2. Hamilton (2020) Tarascon Pocket Pharmacopoeia