Primidone 50mg Tablets
It is used to help control certain kinds of seizures.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Anticonvulsant
Pharmacologic Class
Barbiturate Anticonvulsant
Pregnancy Category
Category D
FDA Approved
Mar 1954
DEA Schedule
Not Controlled
Overview
What is this medicine?
Primidone is a medication used to control certain types of seizures (epilepsy) and a condition called essential tremor. It works by affecting brain activity, partly by being converted into another medicine called phenobarbital. It's important to take it exactly as prescribed, usually starting with a very low dose and slowly increasing it to help your body adjust and reduce side effects.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start to feel better.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry location, avoiding bathrooms. Keep all medications in a secure place, out of the reach of children and pets. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless specifically instructed to do so. Instead, consult with your pharmacist for guidance on the proper disposal method. You may also want to inquire about drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it is close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start to feel better.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry location, avoiding bathrooms. Keep all medications in a secure place, out of the reach of children and pets. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless specifically instructed to do so. Instead, consult with your pharmacist for guidance on the proper disposal method. You may also want to inquire about drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it is close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Do not stop taking this medication suddenly, as it can cause serious withdrawal symptoms or increase seizures. Always consult your doctor before making any changes.
- Avoid alcohol and other medications that cause drowsiness (e.g., cold medicines, pain relievers, sleeping pills) as they can increase sedation and dizziness.
- Be cautious when driving or operating machinery until you know how this medication affects you, as it can cause drowsiness, dizziness, and impaired coordination.
- Women of childbearing potential should use effective contraception, as primidone can reduce the effectiveness of hormonal birth control. Discuss alternative contraception with your doctor.
- Maintain good oral hygiene, as some anticonvulsants can cause gum overgrowth.
- Report any new or worsening mood changes, depression, or suicidal thoughts to your doctor immediately.
Available Forms & Alternatives
Dosing & Administration
Adult Dosing
Standard Dose:
Initial: 50 mg orally at bedtime for 3 days, then 50 mg twice daily for 3 days, then 100 mg 3 times daily for 3 days. Maintenance: 250 mg 3-4 times daily.
Dose Range:
750 - 1500 mg
Condition-Specific Dosing:
epilepsy:
Initial: 50 mg/day, gradually increase by 50-100 mg/day every 3-7 days. Maintenance: 750-1500 mg/day in divided doses.
essential_tremor:
Initial: 50 mg/day, gradually increase by 50 mg every 3-7 days. Maintenance: 250-750 mg/day in divided doses.
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Initial (under 8 years): 50 mg orally at bedtime for 3 days, then 50 mg twice daily for 3 days, then 100 mg 3 times daily for 3 days. Maintenance: 10-25 mg/kg/day in divided doses. Initial (8 years and older): Same as adult initial titration. Maintenance: 250 mg 3-4 times daily.
Adolescent:
Same as adult dosing.
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment recommended, monitor for increased side effects.
Moderate:
Consider reducing dose by 25-50% and/or extending dosing interval. Monitor drug levels (primidone and phenobarbital).
Severe:
Reduce dose by 50% or more and/or extend dosing interval. Monitor drug levels closely.
Dialysis:
Primidone and phenobarbital are dialyzable. Supplemental dose may be needed after hemodialysis. Monitor drug levels.
Hepatic Impairment:
Mild:
Use with caution, monitor for increased side effects.
Moderate:
Consider reducing dose by 25-50%. Monitor drug levels (primidone and phenobarbital) and clinical response.
Severe:
Contraindicated or use with extreme caution and significant dose reduction. Monitor drug levels closely.
Pharmacology
Mechanism of Action
Primidone is an anticonvulsant that is metabolized in the liver to two active metabolites: phenobarbital and phenylethylmalonamide (PEMA). Both primidone and its metabolites contribute to its anticonvulsant activity. The exact mechanism is not fully understood but is thought to involve increasing the threshold for electrical activity in the motor cortex, altering cerebellar function, and enhancing GABAergic neurotransmission (primarily via phenobarbital).
Pharmacokinetics
Absorption:
Bioavailability:
90-100%
Tmax:
Primidone: 3 hours; Phenobarbital: 7-8 hours
FoodEffect:
Food may delay absorption but does not significantly affect the extent of absorption.
Distribution:
Vd:
Primidone: 0.6 L/kg; Phenobarbital: 0.5-1 L/kg
ProteinBinding:
Primidone: 20-30%; Phenobarbital: 40-60%
CnssPenetration:
Yes
Elimination:
HalfLife:
Primidone: 3-23 hours (average 10-12 hours); Phenobarbital: 53-118 hours (average 75-100 hours)
Clearance:
Not available
ExcretionRoute:
Renal (primarily as metabolites, some unchanged drug)
Unchanged:
Primidone: 15-25%; Phenobarbital: 25-50%
Pharmacodynamics
OnsetOfAction:
Days to weeks (due to phenobarbital accumulation)
PeakEffect:
Weeks (due to phenobarbital accumulation)
DurationOfAction:
Variable, dependent on phenobarbital half-life
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Erectile dysfunction (inability to get or maintain an erection)
Changes in vision
Involuntary eye movements
Fever, chills, or sore throat
Swollen lymph nodes
Shortness of breath
Balance problems
Difficulty walking
Like other medications used to treat seizures, this drug may increase the risk of suicidal thoughts or behaviors, particularly in individuals with a history of suicidal ideation or attempts. If you experience any new or worsening symptoms, such as:
Depression
Anxiety, restlessness, or irritability
Panic attacks
Mood or behavioral changes
contact your doctor immediately. If you have suicidal thoughts or attempts, seek help right away.
Other Possible Side Effects
Most medications can cause side effects, but many people may not experience any or may only have mild symptoms. If you notice any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Dizziness, drowsiness, fatigue, or weakness
Nausea, vomiting, or stomach upset
Decreased appetite
This is not an exhaustive list of potential side effects. If you have concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Erectile dysfunction (inability to get or maintain an erection)
Changes in vision
Involuntary eye movements
Fever, chills, or sore throat
Swollen lymph nodes
Shortness of breath
Balance problems
Difficulty walking
Like other medications used to treat seizures, this drug may increase the risk of suicidal thoughts or behaviors, particularly in individuals with a history of suicidal ideation or attempts. If you experience any new or worsening symptoms, such as:
Depression
Anxiety, restlessness, or irritability
Panic attacks
Mood or behavioral changes
contact your doctor immediately. If you have suicidal thoughts or attempts, seek help right away.
Other Possible Side Effects
Most medications can cause side effects, but many people may not experience any or may only have mild symptoms. If you notice any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Dizziness, drowsiness, fatigue, or weakness
Nausea, vomiting, or stomach upset
Decreased appetite
This is not an exhaustive list of potential side effects. If you have concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe skin rash, especially if accompanied by fever, swollen glands, or facial swelling (signs of a serious allergic reaction or DRESS syndrome).
- Unusual bleeding or bruising, persistent sore throat, fever, or chills (signs of blood problems).
- Yellowing of the skin or eyes (jaundice), dark urine, severe stomach pain (signs of liver problems).
- Excessive drowsiness, confusion, or unsteadiness that is worse than expected.
- Any new or worsening seizures or tremor.
- Thoughts of self-harm or suicide.
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you have porphyria, a rare disorder that affects the production of heme, a vital molecule in the body.
Additionally, this medication may interact with other health conditions or medications. To ensure your safety, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are currently taking
Any natural products or vitamins you are using
* Your complete medical history, including any health problems you have or have had in the past
Before starting, stopping, or changing the dose of any medication, including this one, consult with your doctor to confirm that it is safe to do so. This will help prevent potential interactions or adverse effects.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you have porphyria, a rare disorder that affects the production of heme, a vital molecule in the body.
Additionally, this medication may interact with other health conditions or medications. To ensure your safety, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are currently taking
Any natural products or vitamins you are using
* Your complete medical history, including any health problems you have or have had in the past
Before starting, stopping, or changing the dose of any medication, including this one, consult with your doctor to confirm that it is safe to do so. This will help prevent potential interactions or adverse effects.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
When starting this medication, be cautious and avoid driving or engaging in activities that require your full attention until you understand how it affects you.
To minimize the risk of seizures, do not abruptly stop taking this medication without first consulting your doctor. If you need to discontinue use, your doctor will guide you on how to gradually taper off the medication.
Please note that it may take several weeks to experience the full effects of this medication. As directed by your doctor, regular blood tests will be necessary to monitor your condition. Be sure to discuss any concerns or questions with your doctor.
Before consuming alcohol, marijuana, or other forms of cannabis, or taking prescription or over-the-counter medications that may cause drowsiness, consult with your doctor.
If you experience any changes or worsening of seizures after starting this medication, promptly discuss this with your doctor.
If you are using birth control pills or other hormone-based birth control methods, be aware that this medication may reduce their effectiveness. To prevent pregnancy, consider using an additional form of birth control, such as a condom, while taking this medication.
If you are pregnant or become pregnant while taking this medication, immediately contact your doctor, as it may pose a risk to the unborn baby.
If you are breast-feeding, inform your doctor, and discuss any potential risks to your baby.
When starting this medication, be cautious and avoid driving or engaging in activities that require your full attention until you understand how it affects you.
To minimize the risk of seizures, do not abruptly stop taking this medication without first consulting your doctor. If you need to discontinue use, your doctor will guide you on how to gradually taper off the medication.
Please note that it may take several weeks to experience the full effects of this medication. As directed by your doctor, regular blood tests will be necessary to monitor your condition. Be sure to discuss any concerns or questions with your doctor.
Before consuming alcohol, marijuana, or other forms of cannabis, or taking prescription or over-the-counter medications that may cause drowsiness, consult with your doctor.
If you experience any changes or worsening of seizures after starting this medication, promptly discuss this with your doctor.
If you are using birth control pills or other hormone-based birth control methods, be aware that this medication may reduce their effectiveness. To prevent pregnancy, consider using an additional form of birth control, such as a condom, while taking this medication.
If you are pregnant or become pregnant while taking this medication, immediately contact your doctor, as it may pose a risk to the unborn baby.
If you are breast-feeding, inform your doctor, and discuss any potential risks to your baby.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or sedation
- Confusion
- Ataxia (loss of coordination)
- Nystagmus (involuntary eye movements)
- Slurred speech
- Respiratory depression (slow, shallow breathing)
- Hypotension (low blood pressure)
- Hypothermia
- Coma
What to Do:
Call 911 or your local emergency number immediately. For poison control, call 1-800-222-1222. Management typically involves supportive care, maintaining airway, breathing, and circulation, and potentially activated charcoal if ingestion is recent. Hemodialysis may be considered in severe cases due to dialyzability of primidone and phenobarbital.
Drug Interactions
Major Interactions
- Alcohol and other CNS depressants (increased sedation, respiratory depression)
- Oral contraceptives (decreased efficacy of contraceptives)
- Warfarin (decreased anticoagulant effect)
- Doxycycline (decreased doxycycline levels)
- Corticosteroids (decreased corticosteroid levels)
- Cyclosporine, tacrolimus (decreased immunosuppressant levels)
- Lamotrigine (decreased lamotrigine levels)
- Tiagabine (decreased tiagabine levels)
- Valproic acid (increased phenobarbital levels, increased risk of toxicity)
- Phenytoin (variable effects on primidone/phenobarbital levels, increased risk of toxicity)
Moderate Interactions
- Carbamazepine (decreased primidone/phenobarbital levels)
- Topiramate (decreased primidone/phenobarbital levels)
- Felbamate (increased phenobarbital levels)
- Griseofulvin (decreased griseofulvin levels)
- Tricyclic antidepressants (decreased antidepressant levels, increased CNS depression)
- Folic acid (may decrease primidone/phenobarbital levels)
Minor Interactions
- Not available
Monitoring
Baseline Monitoring
Complete Blood Count (CBC) with differential
Rationale: To establish baseline and monitor for blood dyscrasias (e.g., megaloblastic anemia, leukopenia, thrombocytopenia).
Timing: Prior to initiation
Liver Function Tests (LFTs)
Rationale: To establish baseline and monitor for hepatotoxicity.
Timing: Prior to initiation
Renal Function Tests (BUN, Creatinine)
Rationale: To establish baseline and guide dosing in renal impairment.
Timing: Prior to initiation
Serum Primidone and Phenobarbital Levels
Rationale: To establish baseline and guide initial dosing, especially in complex cases or when starting other interacting drugs.
Timing: Prior to initiation (optional, but useful)
Routine Monitoring
Serum Primidone and Phenobarbital Levels
Frequency: Initially after steady state (2-4 weeks), then every 6-12 months or as clinically indicated (e.g., dose changes, new symptoms, suspected toxicity, poor seizure control).
Target: Primidone: 5-12 mcg/mL; Phenobarbital: 15-40 mcg/mL (for seizure control)
Action Threshold: Levels outside therapeutic range, signs of toxicity, or inadequate seizure control.
Complete Blood Count (CBC) with differential
Frequency: Every 6-12 months, or if symptoms of blood dyscrasias develop.
Target: Within normal limits
Action Threshold: Significant decrease in cell counts (e.g., leukopenia, thrombocytopenia, anemia).
Liver Function Tests (LFTs)
Frequency: Every 6-12 months, or if symptoms of hepatic dysfunction develop.
Target: Within normal limits
Action Threshold: Significant elevation of liver enzymes (AST, ALT).
Clinical Assessment for Efficacy
Frequency: Regularly (e.g., every 3-6 months or as needed)
Target: Reduction or elimination of seizures/tremor
Action Threshold: Increased seizure frequency/severity, inadequate tremor control.
Clinical Assessment for Adverse Effects
Frequency: Regularly (e.g., at each visit)
Target: Absence or tolerability of side effects
Action Threshold: Excessive sedation, ataxia, cognitive impairment, rash, mood changes.
Symptom Monitoring
- Drowsiness
- Sedation
- Ataxia (unsteadiness)
- Dizziness
- Nausea
- Vomiting
- Fatigue
- Irritability
- Mood changes (depression, agitation)
- Cognitive impairment (memory, concentration)
- Skin rash
- Fever
- Sore throat
- Unusual bleeding or bruising
- Yellowing of skin or eyes (jaundice)
- Dark urine
- Abdominal pain
Special Patient Groups
Pregnancy
Primidone is classified as Pregnancy Category D. It is associated with an increased risk of major congenital malformations, including neural tube defects, cleft lip/palate, and cardiac defects. Neonatal withdrawal syndrome (irritability, tremors, hypertonia, feeding difficulties) and hemorrhagic disease of the newborn can occur if used during pregnancy. Use only if the potential benefit outweighs the potential risk to the fetus.
Trimester-Specific Risks:
First Trimester:
Highest risk for major congenital malformations (e.g., neural tube defects, facial clefts, cardiac anomalies). Folic acid supplementation (4 mg/day) is recommended for women of childbearing potential.
Second Trimester:
Continued risk of fetal exposure and potential for developmental effects.
Third Trimester:
Risk of neonatal withdrawal syndrome and hemorrhagic disease of the newborn. Vitamin K supplementation (10-20 mg/day) for the mother during the last month of pregnancy, or 1 mg IM for the neonate at birth, may be considered to prevent hemorrhagic disease.
Lactation
Primidone and its active metabolites (phenobarbital, PEMA) are excreted into breast milk. Due to the long half-life of phenobarbital, accumulation can occur in the infant. Breastfeeding is generally not recommended due to the risk of infant sedation, poor feeding, and developmental delay. If breastfeeding, monitor the infant closely for drowsiness, poor suckling, and developmental milestones.
Infant Risk:
L3 (Moderate risk) - Potential for sedation, poor feeding, irritability, and withdrawal symptoms upon discontinuation of breastfeeding. Monitor infant for adverse effects.
Pediatric Use
Children, especially younger ones, may be more susceptible to the sedative effects of primidone. Dosing is weight-based and requires careful titration. Long-term use may affect cognitive development. Regular monitoring of drug levels and clinical response is crucial.
Geriatric Use
Elderly patients may be more sensitive to the sedative and ataxic effects of primidone and its metabolites. Lower initial doses and slower titration are recommended. Increased risk of falls. Monitor renal and hepatic function closely.
Clinical Information
Clinical Pearls
- Primidone is a prodrug to phenobarbital; therefore, phenobarbital levels should also be monitored, as phenobarbital contributes significantly to the therapeutic and toxic effects.
- Slow titration is crucial to minimize initial side effects like sedation, dizziness, and ataxia.
- Patients should be warned about the potential for significant CNS depression, especially when initiating therapy or with concomitant use of other CNS depressants.
- Due to enzyme induction, primidone can reduce the effectiveness of many other medications, including oral contraceptives, warfarin, and certain immunosuppressants. Comprehensive medication review is essential.
- Abrupt discontinuation can precipitate status epilepticus or severe withdrawal symptoms; always taper slowly.
- Consider folic acid supplementation in women of childbearing potential due to the risk of neural tube defects.
Alternative Therapies
- For Epilepsy: Carbamazepine, Phenytoin, Valproic Acid, Lamotrigine, Levetiracetam, Topiramate, Oxcarbazepine, Zonisamide, Gabapentin, Pregabalin.
- For Essential Tremor: Propranolol, Topiramate, Gabapentin, Alprazolam, Botulinum toxin injections (for specific cases).
Cost & Coverage
Average Cost:
$15 - $50 per 30 tablets
Generic Available:
Yes
Insurance Coverage:
Tier 1 or 2 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe use, never share your medication with others or take someone else's medication. This medication is accompanied by a Medication Guide, which is a valuable resource for patients. Please read this guide carefully and review it again whenever you receive a refill of this medication. If you have any questions or concerns about this medication, we encourage you to discuss them with your doctor, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide information about the medication taken, the amount, and the time it occurred.