Does Mysoline (primidone) cause side effects?

Mysoline (primidone) is an anticonvulsant (anti-seizure) medication used alone or with other medications to treat grand mal, psychomotor, or focal epileptic seizures.

It may be effective for grand mal seizures that are not responsive to other anticonvulsants. Mysoline also is used for treating partial seizures and essential tremor.

Its exact mechanism of action is not known. Mysoline is converted into phenobarbital and phenylethylmalonamide (PEMA) in the body. Mysoline, phenobarbital, and PEMA all have anticonvulsant activity. In addition to its anticonvulsant activity, PEMA increases the anticonvulsant activity of phenobarbital. 

Common side effects of Mysoline include

Serious side effects of Mysoline include

Suddenly stopping seizure medications may cause seizures.

Drug interactions of Mysoline include the following because Mysoline may decrease blood levels and the effect of these drugs by increasing the activity of liver enzymes that breakdown these drugs:

  • naloxegol,
  • roflumilast, and
  • lurasidone.

Mysoline has not been adequately evaluated in pregnant women. Some other seizure medications have been associated with birth defects. Mysoline is excreted in human milk and may cause adverse effects in the infant. Consult your doctor before breastfeeding.

What are the important side effects of Mysoline (primidone)?

Common side effects of primidone include:

  • Difficulty speaking (dysarthria)
  • Burning, tingling from damaged nerves (paresthesia)
  • Difficulty moving (ataxia)
  • Loss of balance (vertigo)
  • Paradoxical excitement (children)
  • Hyperactivity (children)
  • Excitement
  • Confusion
  • Depression
  • Drowsiness
  • Irritability
  • Headache
  • Restlessness
  • Nystagmus
  • Dizziness

Possible serious side effects of primidone include:

Seizure medications increase the risk of suicidal thoughts or behavior. Patients treated with seizure medications should be observed for the emergence or worsening of depression, suicidal thoughts or behavior, and unusual changes in mood or behavior.

Suddenly stopping medications for seizures may cause seizures.

Mysoline (primidone) side effects list for healthcare professionals

The most frequently occurring early side effects are ataxia and vertigo. These tend to disappear with continued therapy, or with reduction of initial dosage.

Occasionally, the following have been reported:

  • nausea,
  • anorexia,
  • vomiting,
  • fatigue,
  • hyperirritability,
  • emotional disturbances,
  • sexual impotency,
  • diplopia,
  • nystagmus,
  • drowsiness, and
  • morbilliform skin eruptions.

Other side effects have been reported rarely, such as

  • granulocytopenia,
  • agranulocytosis, and
  • red-cell hypoplasia and aplasia.

These and, occasionally, other persistant or severe side effects may necessitate withdrawal of the drug. Megaloblastic anemia may occur as a rare idiosyncrasy to Mysoline and to other anticonvulsants. The anemia responds to folic acid without necessity of discontinuing medication.

What drugs interact with Mysoline (primidone)?

No information provided.

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Medically Reviewed on 7/6/2020
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Professional side effects and drug interactions sections courtesy of the U.S. Food and Drug Administration.