PHENORBARBITONE 30MG TABLET

Indications

• Generalized tonic-clonic seizures
• Partial seizures
• Status epilepticus
• Sedation in preoperative settings
• Management of withdrawal symptoms in alcohol dependence

Dosage

Children: Refer to the BNF for Children for specific dosing recommendations based on age and weight.

Adults: Refer to the BNF for specific dosing recommendations based on condition and patient factors.

Mechanism of action

Phenobarbital acts by binding to the GABA-A receptor, increasing the duration of chloride channel opening when GABA binds to its receptor. This results in enhanced inhibitory neurotransmission, leading to a sedative and anticonvulsant effect. Additionally, it may also inhibit excitatory neurotransmitter release, contributing to its overall depressant effects on the central nervous system.

Pharmacodynamics

Phenobarbital is characterized by its dose-dependent effects. At lower doses, it exhibits sedative properties, while higher doses produce hypnosis and anesthesia. The drug's primary therapeutic effect is anticonvulsant activity, making it effective in the management of generalized tonic-clonic seizures and partial seizures. Its long duration of action is beneficial for maintaining seizure control, but it can also lead to tolerance and dependence with prolonged use.

Pharmacokinetics

Phenobarbital is well absorbed after oral administration, with peak plasma concentrations occurring within 1 to 2 hours. It is primarily metabolized in the liver through oxidation and conjugation, with a half-life ranging from 53 to 118 hours, which is influenced by factors such as age and liver function. The drug is excreted mainly in urine as metabolites. Its long half-life allows for once-daily dosing in many cases, but it also necessitates careful monitoring for potential accumulation, especially in patients with liver impairment.

Contra-indications

• Porphyria
• Severe respiratory insufficiency
• Severe hepatic impairment
• Hypersensitivity to barbiturates

Adverse effects

• Drowsiness
• Dizziness
• Ataxia
• Nausea
• Vomiting
• Respiratory depression
• Dependence
• Withdrawal symptoms
• Paradoxical reactions in children

Interactions

• CNS depressants (e.g., alcohol, benzodiazepines) may enhance sedative effects
• Oral contraceptives may be less effective due to increased metabolism
• Anticoagulants may have altered effects
• Other enzyme inducers may increase metabolism

Precautions

• Use with caution in patients with a history of substance use disorder
• Monitor for signs of respiratory depression
• Consider potential for drug dependence with prolonged use
• Caution in elderly patients due to increased sensitivity

Pregnancy

Phenobarbital is classified as category D, indicating positive evidence of risk to the fetus. Use only if the potential benefit justifies the potential risk.

Breast-feeding

Phenobarbital is excreted in breast milk. Caution is advised when administering to nursing mothers, as it may affect the infant.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Oral tablets
• Oral elixir
• Injectable solution