Primidone 250mg** Tablets

Primidone is an anticonvulsant that is metabolized in the liver to two active metabolites: phenobarbital and phenylethylmalonamide (PEMA). The anticonvulsant activity is primarily attributed to phenobarbital, which acts by enhancing the effects of gamma-aminobutyric acid (GABA) at GABA-A receptors, leading to increased chloride ion influx and neuronal hyperpolarization, thereby decreasing neuronal excitability. PEMA also has some anticonvulsant activity, though less potent than phenobarbital. Primidone itself may also have some direct anticonvulsant 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
Inability to control eye movements
Fever, chills, or sore throat
Swollen lymph nodes
Shortness of breath
Changes in balance or coordination
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 if they bother you or persist:

Dizziness, drowsiness, fatigue, or weakness
Nausea, vomiting, or upset stomach
Decreased appetite

This is not an exhaustive list of possible side effects. If you have questions or 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.

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, any of its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you have porphyria, a rare genetic disorder that affects the production of heme, a vital molecule in the body.

This list is not exhaustive, and it is crucial to discuss all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, with your doctor and pharmacist. They will help you determine if it is safe to take this medication with your existing medications and health conditions.

Remember, do not start, stop, or change the dosage of any medication without first consulting your doctor to ensure your safety.

It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. This will help ensure they have a complete understanding of your treatment plan.

Until you know how this medication affects you, avoid driving and other activities that require your full attention. This will help prevent accidents and ensure your safety.

Do not suddenly stop taking this medication without consulting your doctor, as this may increase your risk of seizures. If you need to discontinue this medication, your doctor will instruct you on how to gradually taper off the dosage to minimize potential risks.

It may take several weeks to experience the full effects of this medication. Be patient and follow your doctor's instructions.

Regular blood tests will be necessary to monitor your condition. Follow your doctor's recommendations for blood work and discuss any concerns or questions you may have.

Before consuming alcohol, using marijuana or other cannabis products, or taking prescription or over-the-counter medications that may cause drowsiness, consult with your doctor. These substances may interact with your medication and increase the risk of adverse effects.

If you experience changes in your seizure patterns or severity after starting this medication, notify your doctor immediately. They will help you adjust your treatment plan as needed.

If you are using birth control pills or other hormone-based contraceptives, be aware that this medication may reduce their effectiveness. To prevent pregnancy, use an additional form of birth control, such as a condom, while taking this medication.

This medication may harm an unborn baby if taken during pregnancy. If you become pregnant or suspect you may be pregnant while taking this medication, contact your doctor right away.

If you are breastfeeding, inform your doctor. They will help you weigh the potential risks and benefits of continuing to take this medication while nursing your baby.

• Porphyria (acute intermittent porphyria)

• Other CNS depressants (e.g., alcohol, benzodiazepines, opioids, sedating antihistamines): Increased sedation and respiratory depression.
• Oral contraceptives: Decreased efficacy of hormonal contraceptives due to enzyme induction.
• Warfarin: Decreased anticoagulant effect due to enzyme induction.
• Corticosteroids: Decreased corticosteroid effect due to enzyme induction.
• Doxycycline: Decreased doxycycline levels.
• Griseofulvin: Decreased griseofulvin levels.
• Phenytoin, Carbamazepine, Valproic Acid: Altered levels of primidone and/or co-administered AEDs. Valproic acid can inhibit phenobarbital metabolism, increasing phenobarbital levels.
• Chloramphenicol: Increased primidone/phenobarbital levels.
• MAOIs: Increased CNS depression.

• Tricyclic antidepressants: Decreased antidepressant levels, increased CNS depression.
• Beta-blockers (e.g., propranolol, metoprolol): Decreased beta-blocker levels.
• Calcium channel blockers (e.g., verapamil, diltiazem): Decreased calcium channel blocker levels.
• Theophylline: Decreased theophylline levels.
• Digoxin: Decreased digoxin levels.
• Folic acid: May decrease primidone/phenobarbital levels.

• Acetaminophen: Increased metabolism of acetaminophen.
• Vitamin D: May increase vitamin D metabolism, potentially leading to osteomalacia.

• Sedation
• Drowsiness
• Ataxia (unsteadiness)
• Nystagmus (involuntary eye movements)
• Dizziness
• Nausea/Vomiting
• Rash (especially morbilliform or exfoliative dermatitis)
• Mood changes (irritability, depression)
• Cognitive impairment
• Changes in seizure frequency or type
• Signs of blood dyscrasias (e.g., fever, sore throat, unusual bruising/bleeding, pallor)
• Signs of hepatic dysfunction (e.g., jaundice, dark urine, abdominal pain)

Primidone is classified as Pregnancy Category D, indicating positive evidence of human fetal risk. It is associated with an increased risk of major congenital malformations, including cardiac defects, cleft lip/palate, and neural tube defects. Neonatal withdrawal syndrome (e.g., irritability, tremors, hypertonia, feeding difficulties) and hemorrhagic disease of the newborn (due to vitamin K deficiency) can occur if used during pregnancy. Use only if the potential benefit outweighs the potential risk to the fetus, and consider folic acid supplementation before and during pregnancy.

Primidone and its active metabolite phenobarbital are excreted into breast milk. Due to the long half-life of phenobarbital, accumulation can occur in the infant, leading to sedation, poor feeding, and developmental delay. The American Academy of Pediatrics considers phenobarbital (and thus primidone) to be a drug for which the effect on the nursing infant is unknown but may be of concern. Use with caution, monitor infant for sedation, poor feeding, and weight gain. Consider therapeutic drug monitoring of the infant if concerns arise.

Children, especially younger ones, may be more susceptible to CNS side effects (e.g., sedation, irritability, hyperactivity). Dosing is weight-based and requires careful titration. Long-term use may affect bone health (rickets, osteomalacia) and require vitamin D supplementation. Behavioral changes should be monitored.

Elderly patients may be more sensitive to the CNS depressant effects (sedation, dizziness, ataxia) and may require lower initial doses and slower titration. Increased risk of falls. Monitor renal and hepatic function closely, as age-related decline in these functions can affect drug clearance. Polypharmacy increases the risk of drug interactions.

• Primidone is a prodrug to phenobarbital and PEMA; its therapeutic effects and side effects are largely due to phenobarbital.
• Slow titration is crucial to minimize initial CNS side effects like sedation and ataxia.
• Therapeutic drug monitoring of both primidone and phenobarbital levels is often helpful, especially when adjusting doses, assessing adherence, or investigating toxicity/lack of efficacy.
• Patients should be warned about the potential for significant drowsiness and impaired coordination, especially during the initial titration phase.
• Due to enzyme induction, primidone can reduce the effectiveness of many other medications, including oral contraceptives, warfarin, and corticosteroids. Counsel patients accordingly.
• Abrupt discontinuation can precipitate status epilepticus; always taper slowly under medical supervision.
• Consider folic acid supplementation for women of childbearing potential due to teratogenicity risk.

• For Epilepsy: Carbamazepine, Valproic Acid, Lamotrigine, Levetiracetam, Phenytoin, Topiramate, Oxcarbazepine, Zonisamide, Gabapentin, Pregabalin.
• For Essential Tremor: Propranolol, Topiramate, Gabapentin, Alprazolam.

If your symptoms or health problems do not improve or worsen over time, it is essential to contact your doctor for further evaluation and guidance. To ensure your safety and the effectiveness of your treatment, never share your medication with others or take someone else's medication.

This medication is accompanied by a Medication Guide, which is a patient fact sheet that provides crucial information about its safe use. It is vital to read this guide carefully and review it again whenever your prescription is refilled. If you have any questions or concerns about this medication, do not hesitate 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 reporting the incident, be prepared to provide detailed information about the overdose, including the name of the medication taken, the amount consumed, and the time it occurred. This information will help healthcare professionals provide you with the most appropriate care and treatment.