Phenobarbital 15mg Tablets

Phenobarbital is a long-acting barbiturate that non-selectively depresses the central nervous system. It binds to an allosteric site on the GABA-A receptor, enhancing the inhibitory effects of GABA by increasing the duration of chloride channel opening. This leads to neuronal hyperpolarization, decreased neuronal excitability, and inhibition of synaptic transmission. It also inhibits excitatory glutamate receptors (AMPA/kainate) and may have effects on voltage-gated calcium channels.

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
Confusion
Balance problems
Muscle spasms
Bad dreams
Restlessness
Hallucinations (seeing or hearing things that are not there)
Shortness of breath
Slow heartbeat
Feeling extremely tired or weak
Severe dizziness or fainting

Severe Skin Reaction: Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

This rare but serious condition can cause severe health problems and may be life-threatening. Seek medical help immediately if you experience:

Red, swollen, blistered, or peeling skin (with or without fever)
Red or irritated eyes
Sores in your mouth, throat, nose, or eyes

Severe and Potentially Life-Threatening Effects

In rare cases, people taking seizure medications like this one may experience severe and potentially deadly effects. Contact your doctor right away if you notice:

Swollen glands
Fever
Rash
Painful sores in the mouth or around the eyes
Chest pain
Signs of kidney problems, such as:
+ Unable to pass urine
+ Change in the amount of urine passed
Signs of liver problems, such as:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes

Other Possible Side Effects

Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to contact your doctor or seek medical help if you notice any of the following:

Dizziness or drowsiness
Headache
Upset stomach or vomiting
Constipation
Feeling nervous and excitable
* Trouble sleeping

Reporting Side Effects

If you have questions or concerns about side effects, contact 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, its components, or other substances. Be sure to describe the allergic reaction and its symptoms.
Existing health conditions, such as liver disease or breathing difficulties, including shortness of breath.
A history of porphyria, a rare genetic disorder.
Certain heart conditions, including:
+ Heart failure
+ Unstable angina (a type of chest pain)
+ Abnormal heartbeat, such as long QT interval on an electrocardiogram (ECG)
+ Kidney disease
+ Low thyroid function (hypothyroidism)
+ Aortic stenosis, a condition characterized by a very narrow heart valve
Recent heart attack
Use of medications that can cause abnormal heart rhythms, specifically prolonged QT interval. There are many medications that can have this effect, so it is crucial to consult with your doctor or pharmacist if you are unsure.

This list is not exhaustive, and it is vital to discuss all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, with your doctor and pharmacist. They will help determine whether it is safe to take this medication in combination with your other medications and health conditions. Never start, stop, or adjust the dosage of any medication without consulting your doctor first.

Important Warnings and Cautions

When taking this medication, it is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are using this drug.

Risk of Dependence and Withdrawal
The longer you take this medication and the higher the dose, the greater the risk of dependence and withdrawal. Before reducing the dose or stopping this medication, consult your doctor and follow their instructions carefully. Abruptly lowering the dose or stopping this medication can lead to withdrawal, which can be life-threatening. Seek immediate medical attention if you experience any adverse effects.

Tolerance
If you have been taking this medication for an extended period or at high doses, it may become less effective, and you may require higher doses to achieve the same effect. This is known as tolerance. If you notice that the medication is not working as well as it previously did, contact your doctor. Do not take more than the prescribed dose.

Monitoring and Precautions
If you are taking this medication long-term, your doctor may recommend regular blood tests. Discuss this with your doctor. Until you know how this medication affects you, avoid driving and engaging in activities that require alertness. Additionally, avoid consuming alcohol while taking this medication.

Interactions with Other Substances
Before using marijuana, other forms of cannabis, or prescription or over-the-counter medications that may cause drowsiness, consult your doctor.

Suicidal Thoughts and Actions
Like other medications used to treat seizures, this drug may rarely increase the risk of suicidal thoughts or actions, particularly in individuals with a history of suicidal thoughts or actions. If you experience new or worsening symptoms such as depression, anxiety, restlessness, irritability, panic attacks, or mood changes, contact your doctor immediately. If you have suicidal thoughts or actions, seek medical attention right away.

Special Considerations

If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects.
If the patient is a child, use this medication with caution, as the risk of certain side effects may be higher in children.
Birth control pills and other hormone-based birth control methods may be less effective while taking this medication. Use two forms of birth control to prevent pregnancy.
If you are pregnant or become pregnant while taking this medication, contact your doctor immediately, as it may harm the unborn baby.
Taking this medication during the third trimester of pregnancy may lead to side effects or withdrawal in the newborn.
If you are breastfeeding, consult your doctor to discuss any potential risks to your baby.

Seizure-Specific Warnings
If your seizures change or worsen after starting this medication, consult your doctor.

• Porphyria (acute intermittent porphyria, variegate porphyria, hereditary coproporphyria)
• Severe respiratory depression
• Severe hepatic impairment

• Other CNS depressants (e.g., alcohol, opioids, benzodiazepines, tricyclic antidepressants, antihistamines): Increased sedation, respiratory depression, hypotension.
• Valproic acid, valproate: Increased phenobarbital levels (inhibition of metabolism), increased risk of toxicity.
• Oral contraceptives: Decreased efficacy of oral contraceptives (CYP induction).
• Warfarin: Decreased anticoagulant effect (CYP induction).
• Corticosteroids: Decreased corticosteroid effect (CYP induction).
• Doxycycline: Decreased doxycycline levels (CYP induction).
• Griseofulvin: Decreased griseofulvin levels (CYP induction).
• Lamotrigine: Decreased lamotrigine levels (CYP induction).
• Tiagabine: Decreased tiagabine levels (CYP induction).
• Felbamate: Increased phenobarbital levels.
• Vigabatrin: Decreased phenobarbital levels.

• Antidepressants (e.g., SSRIs, TCAs): Altered antidepressant levels, increased CNS depression.
• Antipsychotics: Increased CNS depression.
• Beta-blockers (e.g., metoprolol, propranolol): Decreased beta-blocker levels (CYP induction).
• Calcium channel blockers (e.g., verapamil, diltiazem, nifedipine): Decreased CCB levels (CYP induction).
• Digoxin: Decreased digoxin levels (CYP induction).
• Folic acid: May decrease phenobarbital levels; phenobarbital may decrease folate levels.
• Immunosuppressants (e.g., cyclosporine, tacrolimus): Decreased immunosuppressant levels (CYP induction).
• Methadone: Decreased methadone levels (CYP induction), risk of withdrawal.
• Theophylline/Aminophylline: Decreased xanthine levels (CYP induction).
• Vitamin D: Increased metabolism of vitamin D, potentially leading to osteomalacia.

• Ginkgo biloba: May alter seizure threshold.
• St. John's Wort: May decrease phenobarbital levels (CYP induction).

• Excessive sedation, drowsiness, lethargy
• Ataxia, nystagmus, impaired coordination
• Cognitive impairment, confusion, memory problems
• Respiratory depression, shallow breathing
• Skin rash (including severe reactions like SJS/TEN)
• Paradoxical hyperactivity (especially in children)
• Mood changes, depression, irritability
• Signs of liver dysfunction (e.g., jaundice, dark urine, abdominal pain)
• Signs of hematologic abnormalities (e.g., unusual bruising, bleeding, fever, sore throat)

Phenobarbital is a Category D drug, meaning there is positive evidence of human fetal risk. It is associated with an increased risk of congenital malformations (e.g., cardiac defects, cleft lip/palate, neural tube defects) and a fetal barbiturate withdrawal syndrome if discontinued abruptly near term. Use only if the potential benefit outweighs the potential risk to the fetus.

Phenobarbital is excreted into breast milk. It is rated L3 (Moderately Safe) by LactMed. While some infants may experience sedation, poor feeding, or withdrawal symptoms upon discontinuation, many breastfed infants show no adverse effects. Monitor the infant for drowsiness, poor feeding, and developmental milestones. Consider therapeutic drug monitoring in the infant if concerns arise.

Children, especially younger ones, may experience paradoxical hyperactivity or irritability. Long-term use can affect cognitive development and bone health. Close monitoring of drug levels, growth, and development is crucial. Neonates have significantly longer half-lives and require careful dosing and monitoring.

Elderly patients are more sensitive to the sedative and CNS depressant effects of phenobarbital. They are at increased risk of falls, confusion, and respiratory depression. Lower initial doses and slower titration are recommended. Monitor closely for adverse effects.

• Phenobarbital has a very long half-life, leading to slow achievement of steady-state (weeks) and slow elimination. This means dose adjustments should be made cautiously and effects may not be seen for days to weeks.
• Therapeutic drug monitoring (TDM) is essential due to its narrow therapeutic index, variable pharmacokinetics, and numerous drug interactions.
• It is a potent inducer of multiple CYP450 enzymes and UGT, leading to significant interactions with many other medications, including oral contraceptives, warfarin, and other anticonvulsants.
• Abrupt discontinuation can precipitate severe withdrawal symptoms, including status epilepticus. Taper slowly over weeks to months.
• Despite its age, phenobarbital remains a valuable, inexpensive, and effective anticonvulsant, particularly for generalized tonic-clonic and partial seizures, and in neonatal seizures.
• Consider vitamin D and calcium supplementation for patients on long-term phenobarbital therapy due to the risk of osteomalacia/osteoporosis.

• For epilepsy: Levetiracetam, Valproic acid, Carbamazepine, Lamotrigine, Topiramate, Gabapentin, Pregabalin, Phenytoin, Oxcarbazepine, Zonisamide, Lacosamide, Rufinamide, Clobazam.
• For sedation/anxiety (short-term): Benzodiazepines (e.g., Lorazepam, Diazepam), Z-drugs (e.g., Zolpidem), other sedatives.
• For status epilepticus: Lorazepam, Diazepam, Midazolam, Fosphenytoin, Levetiracetam, Valproic acid.

If your symptoms or health issues persist or worsen, it is essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist. If you have any questions or concerns about this medication, don't hesitate to reach out to your doctor, nurse, 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 what was taken, the amount, and the time it occurred.