Phenobarbital

# Phenobarbital ## Overview - **Classification**: Barbiturate anticonvulsant - **Mechanism**: Enhances GABA-A receptor activity, increasing chloride ion influx and neuronal hyperpolarization, thus decreasing neuronal excitability. Also inhibits AMPA receptors. ## Primary Indications 1. **Seizure Management**: Generalized tonic-clonic and partial seizures. 2. **Status Epilepticus**: Second-line treatment. 3. **Sedation**: Short-term treatment of insomnia (less common now). ## Adult Dosing ### Standard Dosing **Seizure Management / Status Epilepticus (IV Loading Dose)** - **Dose**: **15-20 mg/kg IV** - **Frequency**: Single dose (max **1-1.5 g**). Administer at **50-100 mg/min**. - **Route**: Intravenous (IV) **Seizure Management (Oral/IV Maintenance)** - **Dose**: **30-120 mg/day** - **Frequency**: Once daily or in 2-3 divided doses - **Route**: Oral (PO) or Intravenous (IV) - **Target TDM**: **15-40 mcg/mL** **Sedation/Hypnotic (Oral)** - **Dose**: **30-120 mg/day** - **Frequency**: 2-3 divided doses or a single bedtime dose - **Route**: Oral (PO) ### Dose Adjustments - **Renal Impairment**: Use with caution. CrCl < 10 mL/min: consider dose reduction up to **50%**. Monitor levels. - **Hepatic Impairment**: Significant caution; reduce dose. Monitor LFTs and phenobarbital levels closely. - **Elderly Patients**: Start with lower doses (e.g., **30 mg/day**). Increased sensitivity to CNS depression; higher risk of confusion. ## Pediatric Dosing ### Neonates (0-28 days) **Seizures** - **Loading Dose**: **15-20 mg/kg IV** over 15-30 min. - **Maintenance Dose**: **3-4 mg/kg/day PO/IV** in 1-2 divided doses. - **Maximum**: **5 mg/kg/day** - **Special Notes**: Longer half-life in neonates. Monitor for respiratory depression. ### Infants (1-12 months) **Seizures** - **Loading Dose**: **15-20 mg/kg IV** over 15-30 min. - **Maintenance Dose**: **3-5 mg/kg/day PO/IV** in 1-2 divided doses. - **Maximum**: **8 mg/kg/day** ### Children (1-12 years) **Seizures** - **Loading Dose**: **15-20 mg/kg IV** over 15-30 min. - **Maintenance Dose**: **3-6 mg/kg/day PO/IV** in 1-2 divided doses. - **Maximum**: Up to **12 mg/kg/day** or **120 mg/day** (whichever is lower for chronic use). ### Adolescents (13-18 years) **Seizures** - **Loading Dose**: **15-20 mg/kg IV** - **Maintenance Dose**: **1-5 mg/kg/day** or **30-120 mg/day PO/IV** in 1-3 divided doses. - **Maximum**: **120 mg/day** (for chronic maintenance). ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to barbiturates, porphyria, severe respiratory depression, severe hepatic impairment. - **Relative**: History of substance abuse, unmanaged pain, pre-existing CNS depression. ### Common Adverse Effects - **Very Common (>10%)**: Sedation, drowsiness, lethargy, ataxia. - **Common (1-10%)**: Dizziness, nystagmus, headache, nausea, vomiting, cognitive impairment, irritability (children). - **Serious but Rare**: Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), blood dyscrasias (agranulocytosis, megaloblastic anemia), respiratory depression, suicidal ideation, paradoxical excitement (children/elderly). ### Key Drug Interactions - **CNS Depressants (alcohol, opioids, benzodiazepines)**: Increased risk of profound sedation and respiratory depression. Avoid concurrent use. - **CYP450 Inducers**: Phenobarbital is a potent inducer of CYP2B6, CYP2C, and CYP3A4. - **Oral Contraceptives**: Decreased efficacy; advise alternative contraception. - **Warfarin**: Reduced anticoagulant effect; monitor INR closely, adjust warfarin dose. - **Corticosteroids, Doxycycline, Valproic Acid, Lamotrigine**: Decreased plasma concentrations of these drugs. - **Valproic Acid**: May increase phenobarbital levels by inhibiting metabolism; monitor phenobarbital levels. ## Monitoring & Follow-up - **Before Treatment**: Baseline LFTs, CBC with differential, renal function. - **During Treatment**: Phenobarbital serum levels (therapeutic range **15-40 mcg/mL**), LFTs, CBC, respiratory status, mental status. Monitor seizure frequency. - **Clinical Signs**: Monitor for excessive sedation, respiratory depression, rash, paradoxical excitement, and any signs of suicidality. ## Clinical Pearls - 💡 **Slow IV Administration**: Administer IV phenobarbital slowly to minimize risk of respiratory and cardiovascular depression. - 💡 **Therapeutic Drug Monitoring**: Routine monitoring of serum levels is crucial for optimizing efficacy and minimizing toxicity. - 💡 **Paradoxical Excitement**: Be aware of potential paradoxical excitement or hyperactivity, especially in children and the elderly, rather than sedation. - 💡 **Withdrawal Syndrome**: Abrupt discontinuation can precipitate status epilepticus; taper dose gradually over weeks to months. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.