Phenobarbital 100mg Tablets
WARNING: The use of this drug along with opioid drugs may lead to severe side effects. This includes feeling very sleepy, slow or trouble breathing, passing out, and death. Opioid drugs include drugs like codeine, oxycodone, and morphine. Opioid drugs are used to treat pain and some are used to treat cough. If you have questions, talk with the doctor.If you are taking this drug with an opioid drug, get medical help right away if you feel very sleepy or dizzy; if you have slow, shallow, or trouble breathing; or if you pass out. Caregivers or others need to get medical help right away if the patient does not respond, does not answer or react like normal, or will not wake up. Using this drug for reasons that are not approved may increase the risk for drug use disorder. Misuse or abuse of this drug can lead to overdose or death, especially if used with certain other drugs, alcohol, or street drugs. Get medical help right away if you have changes in mood or behavior, suicidal thoughts or actions, seizures, or trouble breathing. @ COMMON USES: It is used to help control certain kinds of seizures.It is used to treat sleep problems.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Anticonvulsant; Sedative-Hypnotic
Pharmacologic Class
Barbiturate
Pregnancy Category
Category D
FDA Approved
Jan 1970
DEA Schedule
Schedule IV
Overview
What is this medicine?
Phenobarbital is a medication used to control seizures (epilepsy) and to relieve anxiety or help with sleep for a short time. It works by calming the brain and nervous system.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light and moisture. Keep it in a dry place, away from the bathroom. Ensure the lid is tightly closed. Keep your medication in a secure location where children cannot see or reach it, and where others cannot access it. Consider using a locked box or area to store your medication. Keep all medications out of reach of pets.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's 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 a missed one.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light and moisture. Keep it in a dry place, away from the bathroom. Ensure the lid is tightly closed. Keep your medication in a secure location where children cannot see or reach it, and where others cannot access it. Consider using a locked box or area to store your medication. Keep all medications out of reach of pets.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's 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 a missed one.
Lifestyle & Tips
- Take exactly as prescribed, do not stop suddenly without consulting your doctor, as this can cause seizures.
- Avoid alcohol and other medications that cause drowsiness (e.g., cold medicines, pain relievers, sleeping pills) as this can increase sedation and breathing problems.
- Do not drive or operate heavy machinery until you know how this medication affects you, as it can cause drowsiness and dizziness.
- Long-term use may require vitamin D and calcium supplementation to prevent bone problems.
- Report any new or worsening mood changes, depression, or suicidal thoughts to your doctor immediately.
- Wear a medical alert bracelet or carry an identification card stating you take phenobarbital for seizures.
Available Forms & Alternatives
Available Strengths:
- Phenobarbital Sod 65mg/ml Inj, 1ml
- Phenobarbital 97.2mg Tablets
- Phenobarbital 64.8mg Tablets
- Phenobarbital 32.4mg Tablets
- Phenobarbital 16.2mg Tablets
- Phenobarb 130mg/ml Inj, 1ml
- Phenobarbital 100mg Tablets
- Phenobarbital 60mg Tablets
- Phenobarbital 60mg Tablets
- Phenobarbital 15mg Tablets
- Phenobarbital 16.2mg Tablets
- Phenobarbital 32.4mg Tablets
- Phenobarbital 64.8mg Tablets
- Phenobarbital 20mg/5ml Solution
- Phenobarbital 30mg Tablets
- Phenobarbital 97.2mg Tablets
- Phenobarbital 15mg Tablets
Dosing & Administration
Adult Dosing
Standard Dose:
Epilepsy: 60-200 mg/day orally, usually given once daily at bedtime or in divided doses.
Dose Range:
60 - 200 mg
Condition-Specific Dosing:
sedation:
30-120 mg/day orally, in 2-3 divided doses
insomnia:
100-320 mg orally at bedtime (short-term use)
Pediatric Dosing
Neonatal:
Loading dose: 15-20 mg/kg IV; Maintenance: 3-4 mg/kg/day orally or IV, divided every 12-24 hours (adjust based on levels)
Infant:
Loading dose: 15-20 mg/kg IV; Maintenance: 3-5 mg/kg/day orally or IV, divided every 12-24 hours (adjust based on levels)
Child:
Loading dose: 15-20 mg/kg IV; Maintenance: 3-6 mg/kg/day orally or IV, divided every 12-24 hours (adjust based on levels)
Adolescent:
Epilepsy: 1-6 mg/kg/day orally, usually given once daily at bedtime or in divided doses (max 200 mg/day)
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment needed, monitor for increased effects.
Moderate:
Consider dose reduction (e.g., 25% reduction) and monitor serum levels.
Severe:
Significant dose reduction (e.g., 50% reduction) and close monitoring of serum levels and clinical response. Avoid if possible.
Dialysis:
Phenobarbital is dialyzable. Supplemental dose may be needed after dialysis. Monitor serum levels closely.
Hepatic Impairment:
Mild:
Use with caution, monitor for increased effects.
Moderate:
Consider dose reduction (e.g., 25-50% reduction) and close monitoring of serum levels and clinical response.
Severe:
Contraindicated or significant dose reduction (e.g., 50-75% reduction) and very close monitoring. Avoid if possible.
Pharmacology
Mechanism of Action
Phenobarbital is a barbiturate that produces nonselective central nervous system (CNS) depression. It binds to the GABA-A receptor complex, enhancing the inhibitory effects of GABA by increasing the duration of chloride channel opening. This leads to hyperpolarization of the neuronal membrane, decreasing neuronal excitability and raising the seizure threshold. At higher doses, it may also inhibit excitatory neurotransmitter release and directly activate chloride channels.
Pharmacokinetics
Absorption:
Bioavailability:
80-100%
Tmax:
2-12 hours (oral)
FoodEffect:
Food may slightly delay absorption but does not significantly affect the extent of absorption.
Distribution:
Vd:
0.5-1 L/kg
ProteinBinding:
20-45%
CnssPenetration:
Yes
Elimination:
HalfLife:
50-120 hours (adults); 20-70 hours (children)
Clearance:
0.003-0.007 L/kg/hr
ExcretionRoute:
Renal (primarily as inactive metabolites, some unchanged drug)
Unchanged:
25-50%
Pharmacodynamics
OnsetOfAction:
Oral: 30-60 minutes; IV: <5 minutes
PeakEffect:
Oral: 8-12 hours; IV: 30 minutes
DurationOfAction:
6-10 hours (sedative effect); Anticonvulsant effect persists longer due to long 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
Feeling confused
Change in balance
Muscle spasm
Bad dreams
Restlessness
Hallucinations (seeing or hearing things that are not there)
Shortness of breath
Slow heartbeat
Feeling very tired or weak
Severe dizziness or passing out
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
People taking seizure medications like this one may be at risk for severe and potentially deadly effects. Contact your doctor right away if you experience:
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
+ Throwing up
+ Yellow skin or eyes
Other Possible Side Effects
Most people do not experience severe side effects, but some may occur. If you notice any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Feeling dizzy or sleepy
Headache
Upset stomach or throwing up
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.
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
Feeling confused
Change in balance
Muscle spasm
Bad dreams
Restlessness
Hallucinations (seeing or hearing things that are not there)
Shortness of breath
Slow heartbeat
Feeling very tired or weak
Severe dizziness or passing out
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
People taking seizure medications like this one may be at risk for severe and potentially deadly effects. Contact your doctor right away if you experience:
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
+ Throwing up
+ Yellow skin or eyes
Other Possible Side Effects
Most people do not experience severe side effects, but some may occur. If you notice any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Feeling dizzy or sleepy
Headache
Upset stomach or throwing up
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.
Seek Immediate Medical Attention If You Experience:
- Severe drowsiness or dizziness
- Difficulty breathing or shallow breathing
- Unusual weakness or fatigue
- Skin rash, hives, or blistering
- Yellowing of the skin or eyes (jaundice)
- Dark urine or pale stools
- Unusual bleeding or bruising
- Fever, sore throat, or other signs of infection
- Confusion, agitation, or hallucinations
- Paradoxical hyperactivity or irritability (especially in children)
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. Be sure to describe the allergic reaction and its symptoms.
Certain health conditions, such as liver disease or breathing difficulties, like shortness of breath.
A history of porphyria, a rare genetic disorder.
Heart-related 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 consult your doctor or pharmacist if you are unsure.
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions with your doctor and pharmacist. They will help determine if it is safe to take this medication with your existing treatments and health status. Never start, stop, or adjust the dosage of any medication without consulting 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.
Certain health conditions, such as liver disease or breathing difficulties, like shortness of breath.
A history of porphyria, a rare genetic disorder.
Heart-related 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 consult your doctor or pharmacist if you are unsure.
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions with your doctor and pharmacist. They will help determine if it is safe to take this medication with your existing treatments and health status. Never start, stop, or adjust the dosage of any medication without consulting your doctor.
Precautions & Cautions
Important Warnings and Cautions
When taking this medication, it is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, about your treatment.
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 the medication, consult your doctor and follow their instructions carefully. Abruptly lowering the dose or stopping the medication can lead to withdrawal, which can be life-threatening. Seek immediate medical attention if you experience any adverse effects.
Tolerance and Dosage
If you have been taking this medication for an extended period or at high doses, it may lose its effectiveness, and you may require higher doses to achieve the same effect. This is known as tolerance. If you notice the medication is no longer working as well, 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 the 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 medication may rarely increase the risk of suicidal thoughts or actions, particularly in individuals with a history of suicidal behavior. Monitor your mood and behavior, and immediately contact your doctor if you experience any new or worsening symptoms, such as depression, anxiety, restlessness, or mood changes. If you have suicidal thoughts or actions, seek immediate medical attention.
Special Populations
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 and Pregnancy
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. This medication may harm the unborn baby if taken during pregnancy. If you become pregnant or are pregnant, contact your doctor immediately. Taking this medication in the third trimester of pregnancy may lead to side effects or withdrawal in the newborn.
Breastfeeding
If you are breastfeeding, consult your doctor to discuss any potential risks to your baby.
Seizure Management
If your seizures change or worsen after starting this medication, consult your doctor.
When taking this medication, it is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, about your treatment.
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 the medication, consult your doctor and follow their instructions carefully. Abruptly lowering the dose or stopping the medication can lead to withdrawal, which can be life-threatening. Seek immediate medical attention if you experience any adverse effects.
Tolerance and Dosage
If you have been taking this medication for an extended period or at high doses, it may lose its effectiveness, and you may require higher doses to achieve the same effect. This is known as tolerance. If you notice the medication is no longer working as well, 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 the 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 medication may rarely increase the risk of suicidal thoughts or actions, particularly in individuals with a history of suicidal behavior. Monitor your mood and behavior, and immediately contact your doctor if you experience any new or worsening symptoms, such as depression, anxiety, restlessness, or mood changes. If you have suicidal thoughts or actions, seek immediate medical attention.
Special Populations
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 and Pregnancy
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. This medication may harm the unborn baby if taken during pregnancy. If you become pregnant or are pregnant, contact your doctor immediately. Taking this medication in the third trimester of pregnancy may lead to side effects or withdrawal in the newborn.
Breastfeeding
If you are breastfeeding, consult your doctor to discuss any potential risks to your baby.
Seizure Management
If your seizures change or worsen after starting this medication, consult your doctor.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or coma
- Slow, shallow, or absent breathing
- Slow heartbeat
- Low blood pressure
- Cold, clammy skin
- Dilated pupils
- Hypothermia
- Shock
- Kidney failure
What to Do:
Call 911 or your local emergency number immediately. For poison control, call 1-800-222-1222. Overdose requires immediate medical attention, often involving supportive care, respiratory and cardiovascular support, and sometimes activated charcoal or hemodialysis.
Drug Interactions
Contraindicated Interactions
- Porphyria (acute intermittent porphyria)
- Severe respiratory depression
- Known hypersensitivity to barbiturates
Major Interactions
- Other CNS depressants (e.g., alcohol, opioids, benzodiazepines, tricyclic antidepressants, antihistamines) - increased sedation and respiratory depression
- Valproic acid - increased phenobarbital levels (decreased metabolism)
- Warfarin - decreased anticoagulant effect (CYP induction)
- Oral contraceptives - decreased contraceptive efficacy (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)
- Felodipine, Nimodipine, Nisoldipine - decreased calcium channel blocker levels (CYP induction)
- Cyclosporine, Tacrolimus - decreased immunosuppressant levels (CYP induction)
- Ritonavir and other protease inhibitors - decreased protease inhibitor levels (CYP induction)
Moderate Interactions
- Phenytoin - variable effects on both drug levels
- Carbamazepine - decreased carbamazepine levels
- Chloramphenicol - increased phenobarbital levels
- Disulfiram - increased phenobarbital levels
- MAO inhibitors - increased phenobarbital effects
- Rifampin - decreased phenobarbital levels
- Theophylline - decreased theophylline levels (CYP induction)
Minor Interactions
- Folic acid - may decrease phenobarbital levels or increase seizure frequency in some patients
Monitoring
Baseline Monitoring
Complete Blood Count (CBC) with differential
Rationale: To establish baseline and monitor for potential hematologic abnormalities (e.g., megaloblastic anemia, agranulocytosis) with long-term use.
Timing: Prior to initiation of therapy
Liver Function Tests (LFTs) - AST, ALT, alkaline phosphatase, bilirubin
Rationale: To establish baseline and monitor for potential hepatotoxicity.
Timing: Prior to initiation of therapy
Renal Function Tests (RFTs) - BUN, creatinine
Rationale: To establish baseline and assess renal clearance, as a portion of the drug is renally excreted.
Timing: Prior to initiation of therapy
Serum Phenobarbital Level
Rationale: To establish baseline and guide initial dosing, especially in complex cases or when rapid therapeutic levels are desired.
Timing: Prior to initiation or after loading dose
Routine Monitoring
Serum Phenobarbital Level
Frequency: Initially after steady-state (2-3 weeks), then every 6-12 months or as clinically indicated (e.g., dose change, suspected toxicity, loss of seizure control, drug interactions)
Target: 15-40 mcg/mL (therapeutic range for epilepsy)
Action Threshold: Levels >40 mcg/mL may indicate toxicity; levels <15 mcg/mL may indicate subtherapeutic dosing or non-adherence. Adjust dose based on clinical response and levels.
Liver Function Tests (LFTs)
Frequency: Every 6-12 months or as clinically indicated (e.g., signs of liver dysfunction)
Target: Within normal limits
Action Threshold: Significant elevations (e.g., >3x ULN) may warrant dose reduction or discontinuation.
Complete Blood Count (CBC)
Frequency: Every 6-12 months or as clinically indicated (e.g., signs of hematologic abnormalities)
Target: Within normal limits
Action Threshold: Significant abnormalities (e.g., severe anemia, leukopenia, thrombocytopenia) may warrant investigation and potential discontinuation.
Vitamin D and Calcium levels (long-term use)
Frequency: Annually or as clinically indicated
Target: Within normal limits
Action Threshold: Low levels may indicate need for supplementation.
Symptom Monitoring
- Sedation, drowsiness, lethargy
- Dizziness, ataxia, nystagmus
- Cognitive impairment (e.g., memory, concentration)
- Mood changes, irritability, paradoxical hyperactivity (especially in children)
- Rash or other hypersensitivity reactions
- Respiratory depression
- Changes in seizure frequency or type
- Signs of liver dysfunction (e.g., jaundice, dark urine, abdominal pain)
- Signs of hematologic abnormalities (e.g., unusual bruising, bleeding, fever, fatigue)
Special Patient Groups
Pregnancy
Phenobarbital is classified as Pregnancy Category D due to clear evidence of human fetal risk. It is associated with an increased risk of congenital malformations (e.g., cleft lip/palate, cardiac defects, neural tube defects) and neonatal withdrawal syndrome. Use only if the potential benefit outweighs the risk, and discuss risks thoroughly with the patient. Folic acid supplementation is recommended for women of childbearing potential.
Trimester-Specific Risks:
First Trimester:
Increased risk of major congenital malformations (e.g., oral clefts, cardiac anomalies, neural tube defects).
Second Trimester:
Potential for developmental neurotoxicity, though less data than first trimester.
Third Trimester:
Risk of neonatal withdrawal syndrome (irritability, tremors, hypertonia, feeding difficulties) and hemorrhagic disease of the newborn (due to vitamin K deficiency).
Lactation
Phenobarbital is excreted into breast milk and can cause sedation, poor feeding, and withdrawal symptoms in breastfed infants. The American Academy of Pediatrics considers it a drug for which the effect on nursing infants is unknown but may be of concern. Monitor infants closely for drowsiness, poor suckling, and developmental delays. Consider alternative anticonvulsants if possible, or use the lowest effective dose and feed just before the next dose.
Infant Risk:
Moderate risk (L3). Potential for sedation, poor feeding, irritability, and withdrawal symptoms in the infant. Long-term effects on neurodevelopment are not fully established but are a concern.
Pediatric Use
Children, especially younger children, may experience paradoxical hyperactivity or irritability. Close monitoring for behavioral changes is essential. Dosing is weight-based and requires careful titration and therapeutic drug monitoring due to variable pharmacokinetics and long half-life. Neonates are particularly sensitive and require careful monitoring for respiratory depression and sedation.
Geriatric Use
Elderly patients are more sensitive to the CNS depressant effects of phenobarbital (e.g., sedation, dizziness, ataxia) and are at increased risk of falls. They may also have reduced hepatic and renal function, leading to decreased clearance and increased serum levels. Lower initial doses and slower titration are recommended, with close monitoring for adverse effects and serum levels.
Clinical Information
Clinical Pearls
- Phenobarbital has a very long half-life, meaning it takes a long time to reach steady-state (weeks) and to be eliminated from the body. This allows for once-daily dosing but also means dose adjustments take time to show full effect and toxicity can be prolonged.
- Therapeutic drug monitoring (TDM) is crucial for phenobarbital due to its narrow therapeutic index, variable pharmacokinetics, and significant drug interactions.
- It is a potent inducer of multiple CYP450 enzymes, leading to numerous clinically significant drug interactions, particularly with oral contraceptives, warfarin, and other anticonvulsants.
- Abrupt discontinuation can precipitate status epilepticus; therefore, withdrawal should always be gradual.
- Despite its age, phenobarbital remains an effective and inexpensive anticonvulsant, particularly for generalized tonic-clonic and partial seizures, and is still used in resource-limited settings or for refractory epilepsy.
- Patients should be educated about the signs of toxicity (e.g., excessive sedation, ataxia, nystagmus) and the importance of adherence and avoiding alcohol/other CNS depressants.
Alternative Therapies
- Levetiracetam
- Valproic acid
- Carbamazepine
- Phenytoin
- Lamotrigine
- Topiramate
- Oxcarbazepine
- Zonisamide
- Gabapentin
- Pregabalin
- Benzodiazepines (e.g., clonazepam, clobazam for specific seizure types or acute management)
Cost & Coverage
Average Cost:
Check current market data (typically low cost) 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 and effective treatment, 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 for more information. If you have any questions or concerns about your medication, don't hesitate to discuss them with 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 details about the medication taken, the amount, and the time it happened.