What is the dosage and usage of Phenobarbitone (phenobarbital) for treating seizures and insomnia?

Phenobarbital Dosing and Usage

Phenobarbital is indicated as both a sedative and anticonvulsant, with IV loading doses of 15-20 mg/kg for acute seizure management in adults and neonates, achieving therapeutic levels (15-30 mcg/mL) within minutes, followed by maintenance dosing of 3-5 mg/kg/day. 1, 2

Acute Seizure Management (Status Epilepticus)

Loading Dose Protocol

For adults with status epilepticus:

• Initial IV loading dose: 9-12 mg/kg, titrated up to 36 mg/kg if seizures persist 3
• Infusion rate: 100 mg/min 3
• Seizure control achieved in 79% of patients, typically within the first minute of infusion 3
• In emergency department settings, phenobarbital demonstrated shorter cumulative convulsive time and response latency compared to other agents 4

For neonates with seizures:

• Loading dose: 15-20 mg/kg IV 2
• Therapeutic plasma levels (15-30 mcg/mL) reached within minutes and remain stable for 48 hours 2
• Do not add additional anticonvulsants until phenobarbital levels exceed 40 mcg/mL 2
• Phenobarbital and phenytoin show equal efficacy in neonates (43% vs 45% seizure control) 4

Refractory Status Epilepticus

For benzodiazepine-refractory status epilepticus:

• Phenobarbital 30-100 mg/kg IM produces dose-dependent seizure protection 5
• Complete seizure termination achieved with 100 mg/kg within 40 minutes of treatment 5
• Critical caveat: Higher doses (100 mg/kg) cause significant adverse effects including anesthetic/comatose state and do not improve survival rates 5
• In refractory cases, 70% of patients required phenobarbital after high-dose phenytoin failed, but hypotension occurred in all patients requiring vasopressor support 4, 6

Maintenance Therapy

Chronic Seizure Control

Maintenance dosing:

• 3-4 mg/kg/day for neonates 2
• Do not exceed 5 mg/kg/day to avoid drug accumulation (plasma half-life 69-165 hours) 2
• For adults with idiopathic generalized epilepsy: once-daily low-dose phenobarbital provides complete seizure control with no side effects 7

Duration of therapy:

• Neonates: Early discontinuation after 1-2 weeks is generally possible 2
• Adults with generalized epilepsy: Long-term therapy may be required, as discontinuation attempts lead to seizure recurrence 7

Febrile Seizures in Children

Initial dose for febrile convulsions:

• 15 mg/kg IM achieves effective serum levels (15 mcg/mL) within 40 minutes 8
• Oral dosing of 15 mg/kg reaches therapeutic levels in 90 minutes 8
• Maintenance: 5 mg/kg every 24 hours orally or IM until fever resolves 8

Monitoring Requirements

Therapeutic drug monitoring is essential:

• Target therapeutic range: 15-30 mcg/mL 2, 6
• Regular serum phenobarbital level monitoring recommended 6
• Monitor for drug interactions, as phenobarbital is a potent CYP3A4 inducer 6, 9

Safety Considerations and Adverse Effects

Cardiovascular and respiratory:

• Hypotension occurs in all patients with refractory status epilepticus, requiring vasopressor support (typically dopamine) 4, 6
• Respiratory depression is common, especially with rapid administration 6
• Mild adverse effects in standard dosing include prolonged postictal depression of consciousness 3

Efficacy limitations:

• In patients with anoxic or metabolic disturbances, seizure control drops to <40% 4, 6
• Seizures in premature infants are difficult to control with phenobarbital 2

Drug interactions:

• Significant interactions due to CYP3A4 induction require careful monitoring 6, 9
• Behavioral disturbances, irritability, and sleep disturbances may occur 9

Special Clinical Scenarios

Palliative sedation (end-of-life care):

• 1-3 mg/kg SC or IV bolus, followed by 0.5 mg/kg/h infusion 4
• Usual maintenance: 50-100 mg/h 4
• Provides rapid onset and anticonvulsant properties 4
• Adverse effects include paradoxical excitement in elderly, hypotension, nausea/vomiting 4

Prophylactic use:

• Recommended for term neonates with asphyxia and bacterial meningitis 2
• Consider administration before mechanical ventilation with muscle relaxants to improve ventilation efficacy 2