Phenobarbital Sod 65mg/ml Inj, 1ml
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 anxiety.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, GABA-A receptor modulator
Pregnancy Category
Category D
FDA Approved
Jan 1970
DEA Schedule
Schedule IV
Overview
What is this medicine?
Phenobarbital is a medicine used to control seizures (epilepsy) and to help with anxiety or trouble sleeping. It works by calming down overactive brain activity. When given as an injection, it acts quickly, especially for emergencies like severe seizures.
How to Use This Medicine
To use this medication correctly, follow your doctor's instructions and carefully read all the information provided. Adhere to the dosage instructions and administration guidelines. This medication is administered via injection into a muscle or vein.
For proper storage and disposal, consult with your doctor, nurse, or pharmacist to determine the best approach if you need to store this medication at home.
If you miss a dose, contact your doctor promptly to receive guidance on the next steps to take.
For proper storage and disposal, consult with your doctor, nurse, or pharmacist to determine the best approach if you need to store this medication at home.
If you miss a dose, contact your doctor promptly to receive guidance on the next steps to take.
Lifestyle & Tips
- Avoid alcohol and other sedatives: These can increase drowsiness and breathing problems.
- Do not drive or operate machinery: Until you know how this medication affects you, as it can cause drowsiness and dizziness.
- Do not stop taking suddenly: Abrupt discontinuation can lead to withdrawal symptoms or increased seizure frequency. Always consult your doctor.
- Report unusual symptoms: Such as severe skin rash, fever, unusual bleeding/bruising, or yellowing of skin/eyes.
- Maintain good oral hygiene: Long-term use can sometimes lead to gum overgrowth.
- Consider vitamin D and calcium supplementation: Especially with long-term use, to support bone health.
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:
Status Epilepticus: Loading dose 15-20 mg/kg IV (max 100 mg/min); Maintenance 1-3 mg/kg/day IV/IM/PO once daily or divided.
Dose Range:
1 - 20 mg
Condition-Specific Dosing:
statusEpilepticusLoading:
15-20 mg/kg IV, administered at a rate not exceeding 100 mg/min (or 60 mg/min in elderly/debilitated patients). May give additional 5-10 mg/kg if seizures persist, up to a total of 30 mg/kg.
maintenanceAnticonvulsant:
1-3 mg/kg/day IV/IM/PO, usually 60-200 mg/day, given once daily or in divided doses.
sedation:
30-120 mg/day IV/IM/PO in 2-3 divided doses.
Pediatric Dosing
Neonatal:
Loading dose: 15-20 mg/kg IV (over 10-15 min). Maintenance: 3-5 mg/kg/day IV/IM/PO, divided every 12-24 hours. May require higher doses (up to 8 mg/kg/day) to achieve therapeutic levels.
Infant:
Loading dose: 15-20 mg/kg IV (over 10-15 min). Maintenance: 3-5 mg/kg/day IV/IM/PO, divided every 12-24 hours. Some sources suggest up to 6-8 mg/kg/day.
Child:
Loading dose: 15-20 mg/kg IV (over 10-15 min). Maintenance: 3-6 mg/kg/day IV/IM/PO, divided every 12-24 hours.
Adolescent:
Loading dose: 15-20 mg/kg IV (over 10-15 min). Maintenance: 1-3 mg/kg/day IV/IM/PO, usually 60-200 mg/day, given once daily or in divided doses.
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment, monitor for increased sedation.
Moderate:
Consider reducing maintenance dose by 25-50% or extending dosing interval. Monitor serum levels closely.
Severe:
Reduce maintenance dose by 50-75% or extend dosing interval significantly. Monitor serum levels closely.
Dialysis:
Hemodialysis removes phenobarbital. Administer supplemental dose after dialysis (e.g., 25-50% of daily dose). Peritoneal dialysis removes phenobarbital to a lesser extent; monitor levels.
Hepatic Impairment:
Mild:
No specific adjustment, monitor for increased sedation.
Moderate:
Reduce maintenance dose by 25-50%. Monitor serum levels and clinical response closely.
Severe:
Contraindicated or significantly reduce dose (e.g., by 50-75%). Monitor serum levels and clinical response closely. Use with extreme caution due to impaired metabolism and increased risk of toxicity.
Pharmacology
Mechanism of Action
Phenobarbital is a long-acting barbiturate that produces non-selective central nervous system (CNS) depression. Its anticonvulsant activity is primarily due to its ability to enhance the effects of gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the CNS. It binds to a distinct site on the GABA-A receptor complex, increasing the duration of chloride channel opening, leading to hyperpolarization of the neuronal membrane and decreased neuronal excitability. It also inhibits excitatory neurotransmitter release and depresses polysynaptic responses.
Pharmacokinetics
Absorption:
Bioavailability:
100% (IV)
Tmax:
IV: 5-30 minutes (onset of action); IM: 30-60 minutes; Oral: 1-6 hours
FoodEffect:
Not applicable for IV/IM. Oral absorption is not significantly affected by food.
Distribution:
Vd:
0.5-1 L/kg (adults); 0.7-1.2 L/kg (children)
ProteinBinding:
20-60% (variable, decreases with higher concentrations)
CnssPenetration:
Yes (readily crosses blood-brain barrier)
Elimination:
HalfLife:
Adults: 50-120 hours; Children: 20-70 hours; Neonates: 100-500 hours (highly variable)
Clearance:
Adults: 3-10 mL/kg/hr; Children: 5-15 mL/kg/hr
ExcretionRoute:
Renal (25-50% as unchanged drug, remainder as metabolites)
Unchanged:
25-50%
Pharmacodynamics
OnsetOfAction:
IV: 5 minutes; IM: 10-30 minutes
PeakEffect:
IV: 30 minutes; IM: 30-60 minutes
DurationOfAction:
6-10 hours (sedation); 10-12 hours (anticonvulsant effect, can be 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
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 immediate medical attention 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
Other Serious Side Effects
If you experience any of the following symptoms, contact your doctor right away:
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
Administration-Related Side Effects
If this medication is administered too quickly, you may experience:
Trouble breathing
Signs of high or low blood pressure, such as:
+ Severe headache
+ Dizziness
+ Fainting
+ Changes in eyesight
Tell your doctor right away if you experience any of these symptoms.
Tissue Damage
If the medication leaks from the vein, it can cause tissue damage. Inform your nurse immediately if you experience:
Redness
Burning
Pain
Swelling
Blisters
Skin sores
Leaking of fluid at the injection site
Other Side Effects
Most people do not experience significant side effects, but some may occur. If you experience any of the following symptoms, contact your doctor or seek medical attention if they bother you or do not go away:
Dizziness or drowsiness
Headache
Upset stomach or vomiting
Constipation
Feeling nervous and excitable
Trouble sleeping
* Irritation at the injection site
Reporting Side Effects
If you have questions about side effects or want to report any, contact your doctor or call the FDA at 1-800-332-1088. You can also report side effects 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
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 immediate medical attention 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
Other Serious Side Effects
If you experience any of the following symptoms, contact your doctor right away:
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
Administration-Related Side Effects
If this medication is administered too quickly, you may experience:
Trouble breathing
Signs of high or low blood pressure, such as:
+ Severe headache
+ Dizziness
+ Fainting
+ Changes in eyesight
Tell your doctor right away if you experience any of these symptoms.
Tissue Damage
If the medication leaks from the vein, it can cause tissue damage. Inform your nurse immediately if you experience:
Redness
Burning
Pain
Swelling
Blisters
Skin sores
Leaking of fluid at the injection site
Other Side Effects
Most people do not experience significant side effects, but some may occur. If you experience any of the following symptoms, contact your doctor or seek medical attention if they bother you or do not go away:
Dizziness or drowsiness
Headache
Upset stomach or vomiting
Constipation
Feeling nervous and excitable
Trouble sleeping
* Irritation at the injection site
Reporting Side Effects
If you have questions about side effects or want to report any, contact your doctor or call the FDA at 1-800-332-1088. You can also report side effects online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Excessive drowsiness or sedation
- Difficulty breathing or shallow breathing
- Unusual weakness or fatigue
- Confusion or disorientation
- Slurred speech
- Unsteadiness or difficulty walking (ataxia)
- Skin rash, hives, or blistering (especially if severe or spreading)
- Yellowing of the skin or eyes (jaundice)
- Unusual bleeding or bruising
- Fever or sore throat (signs of blood problems)
- Paradoxical excitement or agitation (especially in children or elderly)
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.
Existing health conditions, such as liver disease or breathing difficulties (e.g., shortness of breath).
A history of porphyria, a rare genetic disorder.
Cardiovascular conditions, including heart failure, unstable angina (a type of chest pain), or abnormal heart rhythms (e.g., long QT interval on an electrocardiogram (ECG)).
Kidney disease, hypothyroidism (underactive thyroid), or aortic stenosis (a narrow heart valve).
Recent heart attack.
Use of medications that can cause abnormal heart rhythms (prolonged QT interval). There are numerous medications that can have this effect, so consult your doctor or pharmacist if you are unsure.
Special Considerations for Newborns and Infants:
Some formulations of this medication may contain benzyl alcohol, which can be hazardous to newborns and infants in large quantities. Your doctor will weigh the benefits and risks of using this medication in these cases. If you have concerns about giving this medication to your child, discuss them with your doctor.
Interactions with Other Medications and Health Conditions:
This is not an exhaustive list of all potential interactions. Therefore, it is crucial to inform your doctor and pharmacist about all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, as well as any health conditions you have.
Before starting, stopping, or changing the dosage of any medication, consult your doctor to ensure it is safe to do so in conjunction with this medication.
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 (e.g., shortness of breath).
A history of porphyria, a rare genetic disorder.
Cardiovascular conditions, including heart failure, unstable angina (a type of chest pain), or abnormal heart rhythms (e.g., long QT interval on an electrocardiogram (ECG)).
Kidney disease, hypothyroidism (underactive thyroid), or aortic stenosis (a narrow heart valve).
Recent heart attack.
Use of medications that can cause abnormal heart rhythms (prolonged QT interval). There are numerous medications that can have this effect, so consult your doctor or pharmacist if you are unsure.
Special Considerations for Newborns and Infants:
Some formulations of this medication may contain benzyl alcohol, which can be hazardous to newborns and infants in large quantities. Your doctor will weigh the benefits and risks of using this medication in these cases. If you have concerns about giving this medication to your child, discuss them with your doctor.
Interactions with Other Medications and Health Conditions:
This is not an exhaustive list of all potential interactions. Therefore, it is crucial to inform your doctor and pharmacist about all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, as well as any health conditions you have.
Before starting, stopping, or changing the dosage of any medication, consult your doctor to ensure it is safe to do so in conjunction with this medication.
Precautions & Cautions
Important Warnings and Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. The risk of dependence and withdrawal increases with longer treatment duration and higher doses. 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 may be life-threatening. Seek immediate medical attention if you experience any adverse effects.
If you have been taking this medication for an extended period or at high doses, you may develop tolerance, requiring higher doses to achieve the same effect. If you notice this medication is no longer working as well, contact your doctor. Do not exceed the prescribed dose.
Long-term use of this medication may require regular blood tests. Discuss this with your doctor. Until you understand how this medication affects you, avoid driving and other activities that require alertness. Refrain from consuming alcohol while taking this medication.
Before using marijuana, cannabis, or prescription or over-the-counter medications that may cause drowsiness, consult your doctor. Like other seizure medications, this drug may rarely increase the risk of suicidal thoughts or actions, particularly in individuals with a history of suicidal behavior. Immediately contact your doctor if you experience new or worsening symptoms such as depression, anxiety, restlessness, irritability, panic attacks, or mood changes. If suicidal thoughts or actions occur, seek immediate medical attention.
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects. When used in children, this medication requires careful monitoring, as the risk of certain side effects may be higher.
Birth control pills and other hormone-based contraceptives may be less effective while taking this medication. Use two forms of birth control to prevent pregnancy. If you become pregnant or are planning to become pregnant, inform your doctor, as this medication 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 potential risks to your baby.
Specific Warnings for Seizure Treatment
If your seizures change or worsen after starting this medication, consult your doctor to adjust your treatment plan as needed.
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. The risk of dependence and withdrawal increases with longer treatment duration and higher doses. 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 may be life-threatening. Seek immediate medical attention if you experience any adverse effects.
If you have been taking this medication for an extended period or at high doses, you may develop tolerance, requiring higher doses to achieve the same effect. If you notice this medication is no longer working as well, contact your doctor. Do not exceed the prescribed dose.
Long-term use of this medication may require regular blood tests. Discuss this with your doctor. Until you understand how this medication affects you, avoid driving and other activities that require alertness. Refrain from consuming alcohol while taking this medication.
Before using marijuana, cannabis, or prescription or over-the-counter medications that may cause drowsiness, consult your doctor. Like other seizure medications, this drug may rarely increase the risk of suicidal thoughts or actions, particularly in individuals with a history of suicidal behavior. Immediately contact your doctor if you experience new or worsening symptoms such as depression, anxiety, restlessness, irritability, panic attacks, or mood changes. If suicidal thoughts or actions occur, seek immediate medical attention.
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects. When used in children, this medication requires careful monitoring, as the risk of certain side effects may be higher.
Birth control pills and other hormone-based contraceptives may be less effective while taking this medication. Use two forms of birth control to prevent pregnancy. If you become pregnant or are planning to become pregnant, inform your doctor, as this medication 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 potential risks to your baby.
Specific Warnings for Seizure Treatment
If your seizures change or worsen after starting this medication, consult your doctor to adjust your treatment plan as needed.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or coma
- Slow, shallow, or stopped breathing (respiratory depression)
- Low blood pressure (hypotension)
- Slow heart rate (bradycardia)
- Hypothermia
- Pulmonary edema
- Kidney failure
- Shock
What to Do:
Seek immediate medical attention. Call 911 or Poison Control (1-800-222-1222). Treatment involves supportive care, maintaining airway and breathing, IV fluids, and sometimes activated charcoal (if oral ingestion) or hemodialysis for severe cases.
Drug Interactions
Contraindicated Interactions
- Porphyria (acute intermittent porphyria)
- Severe respiratory depression
- Severe hepatic impairment (relative contraindication)
Major Interactions
- Other CNS depressants (e.g., opioids, benzodiazepines, alcohol, tricyclic antidepressants, antihistamines): Increased sedation, respiratory depression, hypotension.
- Valproic acid, valproate: Increased phenobarbital levels (inhibition of metabolism), increased CNS depression.
- Felbamate: Increased phenobarbital levels.
- Chloramphenicol: Increased phenobarbital levels.
- Oral anticoagulants (e.g., 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).
- Phenytoin: Variable interaction; can increase or decrease phenytoin levels, or phenobarbital levels.
- Carbamazepine: Decreased carbamazepine levels (CYP induction).
- Tiagabine: Decreased tiagabine levels (CYP induction).
- Topiramate: Decreased topiramate levels (CYP induction).
- Zidovudine: Decreased zidovudine levels (CYP induction).
Moderate Interactions
- Acetaminophen: Increased risk of hepatotoxicity with chronic phenobarbital use.
- Digoxin: Decreased digoxin levels (CYP induction).
- Folic acid: May decrease phenobarbital levels; phenobarbital may increase folate requirements.
- Quinine: Decreased quinine levels (CYP induction).
- Rifampin: Decreased phenobarbital levels (potent CYP induction).
- Theophylline: Decreased theophylline levels (CYP induction).
- Verapamil: Decreased verapamil levels (CYP induction).
Minor Interactions
- Ginkgo biloba: May decrease phenobarbital efficacy.
- St. John's Wort: May decrease phenobarbital levels (CYP induction).
Monitoring
Baseline Monitoring
Liver Function Tests (LFTs)
Rationale: To assess baseline hepatic function as phenobarbital is metabolized by the liver and can cause hepatotoxicity.
Timing: Prior to initiation of therapy.
Renal Function Tests (BUN, Creatinine)
Rationale: To assess baseline renal function as a portion of phenobarbital is renally excreted and dose adjustments may be needed in renal impairment.
Timing: Prior to initiation of therapy.
Complete Blood Count (CBC) with differential
Rationale: To assess for baseline hematologic abnormalities, as phenobarbital can rarely cause blood dyscrasias.
Timing: Prior to initiation of therapy.
Electrolytes (especially Calcium, Phosphate)
Rationale: Chronic phenobarbital use can affect bone metabolism and lead to hypocalcemia.
Timing: Prior to initiation of therapy.
Routine Monitoring
Phenobarbital Serum Levels (Therapeutic Drug Monitoring)
Frequency: Initially 2-4 weeks after initiation or dose change, then every 3-6 months or as clinically indicated (e.g., seizure recurrence, signs of toxicity).
Target: 15-40 mcg/mL (for anticonvulsant effect); lower for sedation (e.g., 5-15 mcg/mL).
Action Threshold: Levels >40 mcg/mL associated with increased toxicity (sedation, nystagmus, ataxia). Levels <15 mcg/mL may indicate subtherapeutic dosing.
Liver Function Tests (LFTs)
Frequency: Every 6-12 months, or if signs/symptoms of hepatic dysfunction develop.
Target: Within normal limits.
Action Threshold: Significant elevation (e.g., >3x ULN) may warrant dose reduction or discontinuation.
Complete Blood Count (CBC) with differential
Frequency: Annually, or if signs/symptoms of hematologic abnormalities (e.g., fever, sore throat, bruising) develop.
Target: Within normal limits.
Action Threshold: Significant abnormalities (e.g., leukopenia, thrombocytopenia) may warrant investigation.
Vitamin D levels and Bone Mineral Density (BMD)
Frequency: Consider periodically for long-term therapy, especially in at-risk populations.
Target: Adequate vitamin D levels; stable BMD.
Action Threshold: Low vitamin D or osteopenia/osteoporosis may require supplementation or alternative therapy.
Symptom Monitoring
- Sedation
- Drowsiness
- Lethargy
- Ataxia
- Nystagmus
- Dizziness
- Confusion
- Respiratory depression (especially with rapid IV administration or high doses)
- Hypotension (with rapid IV administration)
- Skin rash (Stevens-Johnson syndrome, toxic epidermal necrolysis - rare but serious)
- Paradoxical hyperactivity/agitation (especially in children and elderly)
- Mood changes
- Cognitive impairment
Special Patient Groups
Pregnancy
Phenobarbital is classified as Pregnancy Category D, indicating positive 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 a neonatal withdrawal syndrome (irritability, hypertonia, tremors, feeding difficulties) if used during the third trimester. Folic acid supplementation is recommended for women of childbearing potential.
Trimester-Specific Risks:
First Trimester:
Increased risk of major congenital malformations (e.g., cleft lip/palate, cardiac defects, neural tube defects).
Second Trimester:
Continued risk of malformations, though less studied than first trimester. Potential for neurodevelopmental effects.
Third Trimester:
Risk of neonatal withdrawal syndrome (irritability, hypertonia, tremors, feeding difficulties, respiratory depression) 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 the nursing infant is unknown but may be of concern. Monitor infants for sedation, poor weight gain, and developmental milestones. Use with caution, or consider alternative agents if possible.
Infant Risk:
Moderate risk (L3). Potential for infant sedation, poor feeding, withdrawal symptoms upon discontinuation of breastfeeding. Monitor infant closely.
Pediatric Use
Children, especially younger children, may exhibit paradoxical hyperactivity or agitation instead of sedation. Neonates and infants have significantly longer half-lives due to immature hepatic metabolism, requiring careful dose titration and monitoring. Higher maintenance doses per kg may be needed in older children due to faster metabolism.
Geriatric Use
Elderly patients are more sensitive to the sedative and CNS depressant effects of phenobarbital due to decreased hepatic and renal function, and reduced protein binding. They are at increased risk of falls, confusion, and respiratory depression. Lower initial doses and slower titration are recommended. Avoid use if possible due to Beers Criteria.
Clinical Information
Clinical Pearls
- Phenobarbital has a very long half-life, meaning it takes a long time to reach steady-state levels (weeks) and to be eliminated from the body. This makes dose adjustments slow and requires patience.
- Therapeutic drug monitoring (TDM) is crucial for phenobarbital to ensure efficacy and minimize toxicity, especially given its narrow therapeutic index.
- Rapid IV administration can cause severe hypotension and respiratory depression. Administer slowly, typically no faster than 100 mg/min (or 60 mg/min in elderly/debilitated patients).
- Phenobarbital is a potent inducer of multiple CYP450 enzymes, leading to numerous significant drug interactions that can decrease the efficacy of co-administered medications.
- Abrupt discontinuation can precipitate status epilepticus or severe withdrawal symptoms. Taper slowly over weeks to months.
- Despite its older age, phenobarbital remains a valuable agent for status epilepticus, especially refractory cases, and for certain types of seizures (e.g., febrile seizures in some cases, neonatal seizures).
Alternative Therapies
- For Status Epilepticus: Lorazepam, Diazepam, Midazolam, Fosphenytoin, Levetiracetam, Valproic acid.
- For Seizure Prophylaxis: Carbamazepine, Valproic acid, Phenytoin, Lamotrigine, Levetiracetam, Topiramate, Oxcarbazepine, Gabapentin, Pregabalin.
- For Sedation/Insomnia: Benzodiazepines (e.g., Temazepam, Zolpidem), non-benzodiazepine hypnotics (e.g., Z-drugs), antihistamines (e.g., Diphenhydramine).
Cost & Coverage
Average Cost:
Varies widely, typically $5-$20 per 1ml vial (65mg/ml) per 1ml vial
Generic Available:
Yes
Insurance Coverage:
Tier 1 or 2 (Generic)
General Drug Facts
If your symptoms or health problems persist or worsen, it is essential to contact your doctor promptly. To ensure safe use, never share your medication with others, and do not take medication prescribed for someone else. Store all medications in a secure location, out of reach of children and pets, to prevent accidental ingestion. Dispose of unused or expired medications properly. Unless instructed otherwise, do not flush medications down the toilet or pour them down the drain. If you are unsure about the correct disposal method, consult your pharmacist, who can also inform you about potential drug take-back programs in your area. Some medications may come with an additional patient information leaflet, which your pharmacist can provide. If you have any questions or concerns about your medication, discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately contact your local poison control center or seek medical attention. Be prepared to provide information about the medication taken, the quantity, and the time of ingestion.