Phenobarbital

How it works

It enhances the action of the inhibitory neurotransmitter GABA at the GABA-A receptor by prolonging chloride channel opening, increasing inhibitory tone and raising the seizure threshold.

Prescribing in practice

• It causes dose-related sedation and can produce respiratory depression, so facilities for respiratory support must be available, particularly when loading or used with other CNS depressants.
• It is a hepatic enzyme inducer and can interact with many co-administered drugs, and it has a narrow therapeutic margin.
• Loading and maintenance should follow a children's formulary and the SPC, with maintenance guided by clinical response and serum concentrations.

Monitoring

Monitor seizure control, level of consciousness, respiration and serum phenobarbital concentrations, particularly when adjusting therapy.

Counselling the patient

• Explain to parents that the medicine is used to control the baby's seizures and may make the baby drowsy.
• The neonatal team will monitor breathing and may take blood tests to check drug levels.
• Do not stop the medicine abruptly, as this can provoke further seizures.

Evidence & guidelines

Phenobarbital remains the established first-line agent for neonatal seizures in UK practice, although controlled trials show overall seizure control with monotherapy is often incomplete.