primidone (Rx)

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Brand and Other Names:Mysoline

Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

tablets

  • 50mg
  • 250mg
more...

Seizures (Psychomotor, Focal, & Grand Mal)

Initial: 100-125 mg PO qHS for 3 days, THEN

100-125 mg BID for 3 days, THEN

100-125 mg TID for 3 days, THEN

250 mg TID-QID; not to exceed 2 g/day

Dosing considerations

  • May take with food
  • Monitor: CBC, SMA-12 q6mo
  • Do not exceed 2 g/day
  • May control grand mal seizures refractory to other anticonvulsants
  • Do not abruptly discontinue, due to risk of precipitation of status epilepticus
  • Therapeutic efficacy of dosage regimen may take several weeks to assess

Essential Tremor

12.5-25 mg/day PO HS

Increase dose over 2-3 weeks to 250 mg PO qDay or divided BID; do not exceed 750 mg/day

Partial Seizures

125 mg PO QHS

Increase dose every 3 days by 125 mg if needed to 250 mg q12hr; do not exceed 500 mg/day

Dosage Forms & Strengths

tablets

  • 50mg
  • 250mg
more...

Seizures (Psychomotor, Focal, & Grand Mal)

Initial: 50 mg PO qHS for 3 days, THEN

50 mg BID for 3 days, THEN

100 mg BID for 3 days, THEN

After 9th day: 125-250 mg PO TID, OR 10-25 mg/kg/day divided q8hr PO 

Dosing Considerations

May take with food

Monitor: CBC, SMA-12 q6mo

Do not exceed 2 g/day

May control grand mal seizures refractory to other anticonvulsants

Do not abruptly discontinue, due to risk of precipitation of status epilepticus

Therapeutic efficacy of dosage regimen may take several weeks to assess

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Interactions

Interaction Checker

and primidone

No Results

     activity indicator 
    No Interactions Found
    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

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            Adverse Effects

            1-10%

            Dysarthria

            Paresthesia

            Ataxia

            Vertigo

            Pediatric patients

            • Paradoxical excitement
            • Hyperactivity

            Geriatric patients

            • Excitement
            • Confusion
            • Depression

            Adverse effects that decrease with continued treatment

            • Drowsiness
            • Ataxia
            • Irritability
            • Headache
            • Restlessness
            • Nystagmus
            • Dizziness
            • Vertigo

            Frequency Not Defined

            Acute psychosis (rare)

            Nausea

            Vomiting

            Constipation

            Diarrhea

            Megaloblastic (folate-deficiency) anemia

            Hepatotoxicity

            Hypocalcemia

            Rickets (rare)

            Osteomalacia (rare)

            Rash

            Stevens-Johnson syndrome (rare)

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            Warnings

            Contraindications

            Porphyria

            Hypersensitivity to phenobarbital

            Cautions

            Do not interchange brands, due to bioequivalence issues

            May cause hyperexcitability, especially in children

            When replacing another antiseizure drug, gradually increase dosage of primidone while gradually decreasing dosage of other drug over at least 2 weeks

            Withdraw gradually, due to risk of precipitation of status epilepticus

            Limited number of reports indicate maintaining serum concentration of 5-12 mcg/mL is necessary

            Inhibits transplacental vitamin K transport, leading to increased risk of fetal hemorrhage

            May render OCPs ineffective

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            Pregnancy & Lactation

            Pregnancy category: D; continue use if pregnant; consider vitamin K supplementation for 1 month before birth

            Lactation: Distributed in breast milk; discontinue if drug effects occur in nursing infant

            Pregnancy Categories

            A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA:Information not available.

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            Pharmacology

            Mechanism of Action

            Metabolized to phenobarbital

            Absorption

            Bioavailability: 60-80%

            Peak plasma time: 4 hr

            Metabolism

            Metabolized by liver

            Metabolites: Phenobarbital, phenylethylmalonamide

            Enzymes induced: CYP3A4

            Elimination

            Half-life: 10-12 hr; 24-48 hr (metabolites)

            Dialyzable: Yes

            Excretion: Urine (15-25%)

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            Formulary

            FormularyPatient Discounts

            Adding plans allows you to compare formulary status to other drugs in the same class.

            To view formulary information first create a list of plans. Your list will be saved and can be edited at any time.

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            • View the formulary and any restrictions for each plan.
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            • Compare formulary status to other drugs in the same class.
            • Access your plan list on any device – mobile or desktop.

            The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
            QL Quantity Limits
            Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
            ST Step Therapy
            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
            OR Other Restrictions
            Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.
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