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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Cost: Medications

primidone (on 5/17/2017 at Medicaid.Gov Survey of pharmacy drug pricing)
PRIMIDONE 250 MG TABLET Generic $0.15 each
PRIMIDONE 50 MG TABLET Generic $0.08 each

Ontology: Primidone (C0033148)

Definition (NCI) An analog of phenobarbital with antiepileptic property. Although the mechanism of action has not been fully elucidated, primidone probably exerts its actions, in a manner similar to phenobarbital, via activation of gamma-aminobutyric acid (GABA)-A receptor/chloride ionophore complex, which leads to prolonged and increased frequency of opening of the chloride channel within the receptor complex. This results in an alteration in the electrical activity of the nerve cell membrane, causing hyperpolarization and prevention of partial and tonic-clonic seizures. In addition, this agent is partially metabolized to phenobarbital and phenylethylmalonamide (PEMA), which may also contribute to its anti-seizure properties.
Definition (MSH) An antiepileptic agent related to the barbiturates; it is partly metabolized to PHENOBARBITAL in the body and owes some of its actions to this metabolite. Adverse effects are reported to be more frequent than with PHENOBARBITAL. (From Martindale, The Extra Pharmacopoeia, 30th ed, p309)
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D011324
SnomedCT 371193009, 387256009, 47120002
LNC LP14730-3, MTHU003369
English Primidone, Desoxyphenobarbital, Misodine, 4,6(1H,5H)-Pyrimidinedione, 5-ethyldihydro-5-phenyl-, 2-Deoxyphenobarbital, Mysedon, primidone, PRIMIDONE, primidone (medication), Primidone [Chemical/Ingredient], Primidone product (product), Primidone product, Hexamidinum, Primidone (product), Primidone (substance)
Swedish Primidon
Czech primidon
Finnish Primidoni
Russian DEZOKSIFENOBARBITAL, PRIMIDON, GEKSAMIDIN, PRIMAKLON, ГЕКСАМИДИН, ДЕЗОКСИФЕНОБАРБИТАЛ, ПРИМАКЛОН, ПРИМИДОН
Japanese プリマクロン, デスオキシフェノバルビタール, プリミドン
Polish Prymidon, Mizodin
Spanish primidona, producto, primidona, producto (producto), desoxifenobarbital, primidona (producto), primidona (sustancia), primidona, Primidona, Desoxifenobarbital
French Désoxyphenobarbitone, Primaclone, Primidone
German Desoxyphenobarbital, Primidon
Italian Primidone
Portuguese Desoxifenobarbital, Primidona

Ontology: Mysoline (C0700016)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D011324
English mysoline, Mysoline, Astra Brand of Primidone, AstraZeneca Brand of Primidone, Draxis Brand of Primidone, Mylepsinum, Xcel Brand of Primidone, Zeneca Brand of Primidone