Description

Phenobarbital sodium injection 200mg/ml is a medication used to control and prevent seizures, including generalized tonic-clonic and partial seizures. It is also utilized in the acute treatment of status epilepticus, a life-threatening condition characterized by continuous or rapidly recurring seizures.

**Drug Class:**
Phenobarbital belongs to the class of anticonvulsant medications known as barbiturates.

**Mechanism of Action:**
Phenobarbital stabilizes neuronal membranes and reduces seizure activity by inhibiting sodium ion influx during neuronal depolarization, thereby decreasing the excitability of neurons.

**Common Forms:**
Phenobarbital is available in various forms, including oral tablets, chewable tablets, oral suspension, and intravenous injection.

**Dosage Instructions:**
For adults experiencing status epilepticus who have not previously received phenobarbital, an initial loading dose of 20mg per kilogram of body weight is recommended. This dose should be administered intravenously over 20 minutes. For patients already on phenobarbital therapy but not adequately controlled, a ‘top-up’ dose may be calculated using the formula:

Phenobarbital sodium ‘top-up’ dose (mg) = (20 – measured concentration (mg/L)) x 0.7 x weight (kg)

Maintenance doses typically range from 3 to 5mg per kilogram of body weight per day, divided into two doses. The first maintenance dose is usually administered 12 to 24 hours after the loading dose. Intravenous phenobarbital should be administered at a rate not exceeding 50mg per minute to minimize the risk of adverse effects. In patients who are elderly or have pre-existing cardiac conditions, the infusion rate should be reduced to 25mg per minute. Continuous monitoring of ECG, blood pressure, and respiratory function is essential during the infusion.

For pediatric patients, the dosing regimen may differ. For example, in neonates, a loading dose of 20mg/kg is administered intravenously over 10 to 15 minutes, with maintenance doses of 3-5mg/kg once daily. However, dosing should be individualized based on the patient’s clinical response and tolerance.

Phenobarbital is contraindicated in patients with hypersensitivity to phenobarbital or other barbiturates, severe respiratory depression, acute intermittent porphyria, and severe impairment of renal or hepatic function. It should be used with caution in patients with a history of alcohol or drug abuse, as it may cause addiction. Sudden withdrawal can lead to symptoms such as sleeplessness, anxiety, tremor, dizziness, nausea, seizures, and delirium. Therefore, any discontinuation should be gradual and under medical supervision.

Common side effects include drowsiness, dizziness, and ataxia. Serious adverse effects can include cardiovascular events, such as hypotension and arrhythmias, especially when administered rapidly. Long-term use may lead to gingival hyperplasia, hirsutism, and coarsening of facial features. Regular monitoring of phenobarbital serum levels is recommended to ensure therapeutic efficacy and minimize toxicity.