What is primidone (Mysoline)? How does it work (mechanism of action)?
Primidone, brand name Mysoline, is an oral anticonvulsant (anti-seizure) medication used for treating several types of seizures. Its exact mechanism of action is not known. Primidone is converted into phenobarbital and phenylethylmalonamide (PEMA) in the body. Primidone, phenobarbital, and PEMA all have anticonvulsant activity. In addition to its anticonvulsant activity, PEMA increases the anticonvulsant activity of phenobarbital. The FDA approved primidone in March, 1954.
What are the uses for primidone?
Primidone is used alone or with other medications for treating grand mal, psychomotor, or focal epileptic seizures. It may be effective for grand mal seizures that are not responsive to other anticonvulsants. Primidone should not be used by patients with porphyria and people who are allergic to phenobarbital. It also is used for treating partial seizures and essential tremor.
What are the side effects of 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)
Possible serious side effects of primidone include:
- Acute psychosis
- Folate-deficiency anemia
- Liver toxicity
- Low blood calcium
- Weakening of bones
- Serious skin reactions (for example, Stevens-Johnson syndrome)
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.
- What is primidone (Mysoline)? How does it work (mechanism of action)?
- What are the uses for primidone?
- What are the side effects of primidone?
- What is the dosage for primidone?
- Which drugs or supplements interact with primidone?
- Is primidone safe to take if I am pregnant or breastfeeding?
- What else should I know about primidone?
What is the dosage for primidone?
To treat psychomotor, focal, or grand mal seizures
- Patients 8 years of age or older should be treated with the following regimen:
- Days 1 to 3: 100 to 125 mg at bedtime.
- Days 4 to 6: 100 to 125 mg twice daily.
- Days 7 to 9: 100 to 125 mg three times daily.
- Day 10 to maintenance: 250 mg three or four times daily.
- The maximum dose is 2 g daily.
- It takes several weeks before the antiseizure effects of primidone are seen.
To treat partial seizures
- The initial dose is 125 mg at bedtime. Increase the dose by 125 mg every 3 days to 250 mg every 12 hours if needed. The maximum dose is 500 mg daily.
Which drugs or supplements interact with primidone?
Primidone may decrease blood levels and the effect of several drugs by increasing the activity of liver enzymes that breakdown these drugs. Examples of drugs affected by Primidone include naloxegol (Movantik), roflumilast (Daliresp), lurasidone (Latuda), and many others.
Is primidone safe to take if I am pregnant or breastfeeding?
Primidone has not been adequately evaluated in pregnant women. Some other seizure medications have been associated with birth defects. Primidone is excreted in human milk and may cause adverse effects in the infant.
- Epileptic seizures
- Grand mal seizures
- Psychomotor seizures.
- Treat partial seizures and essential tremor
Researchers do not knew exactly how primidone works in the body. Antiepileptic drugs (AEDs), for example, primidone (Mysoline), increase the risk of suicidal thoughts in patients taking antiepileptic drugs regardless of why your doctor has prescribed them to you.
The most common side effects are vertigo and poor coordination and unsteadiness). Less frequent side effects include:
- Sexual impotency
- Morbilliform skin eruptions
- Double vision (diplopia)
- Involuntary eye movements that are rapid, rhythmic, and repetitious (nystagmus)
Rare side effects include:
- Red cell hypoplasia and aplasia
If persistent or severe side effects persist, the drug may need to be withdrawn. Researchers do not know the risks of taking primidone during pregnancy or while breastfeeding. Pregnant women with epilepsy who are taking anticonvulsant drugs have an increased risk of having a child with birth defects. Primidone is secreted in breast milk, but there are no tests to determine how much of the drug is secreted. Therefore, doctors do not recommend taking primidone if you are breastfeeding.
REFERENCE: Primidone FDA Prescribing Information.
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