phenobarbital sodium: clinical use

Prescribing considerations

• Confirm seizure type because absence and myoclonic seizures may not respond and can be aggravated.
• Avoid abrupt withdrawal because dependence, withdrawal symptoms and rebound seizures can occur.
• Review the extensive enzyme-inducing interaction burden, including contraception, anticoagulants, antivirals and other antiseizure treatments.
• Use particular caution with respiratory disease, depression, older or debilitated patients, renal or hepatic impairment, pregnancy and a history of substance dependence.
• The injection contains a high proportion of propylene glycol and requires product-specific parenteral precautions.

Contraindications and cautions

• Hypersensitivity to phenobarbital, another barbiturate or a formulation excipient.
• Severe respiratory depression.
• Acute intermittent porphyria.
• Severe renal or hepatic impairment.
• The oral suspension has additional product-specific contraindications, including hyperkinetic children and several strong interacting medicines or St John’s wort.
• Do not restart phenobarbital after phenobarbital-associated Stevens–Johnson syndrome or toxic epidermal necrolysis.

Monitoring

• Assess seizure control, sedation, cognition, coordination, behaviour, mood and suicidal ideation.
• Monitor promptly for rash, systemic hypersensitivity and hepatic injury, especially early in treatment.
• Consider phenobarbital concentration monitoring where clinically justified, including suspected toxicity, altered seizure control, pregnancy or interacting-treatment changes.
• Consider hepatic, renal, haematological, folate and bone-health assessment according to clinical context and treatment duration.
• Monitor interaction-specific outcomes such as INR, thyroid status or concentrations of other antiseizure treatments when indicated.

Clinical pharmacology

A long-acting barbiturate that enhances GABA-A-mediated chloride influx and depresses neuronal excitability. It has slow oral absorption, a long and variable elimination half-life, partial hepatic metabolism, urinary elimination and strong hepatic enzyme-inducing effects.

Formulation and product differences

• The oral suspension is supplied with a graduated oral syringe and adapter, must be shaken, and can be administered through compatible nasogastric or gastrostomy tubes.
• The oral suspension contains sodium benzoate, which may worsen jaundice in newborn infants, and contains sodium.
• The injection is a clear alkaline solution containing propylene glycol, disodium edetate and water for injections; it is administered by a healthcare professional.
• Intravenous injection requires the product-specific dilution procedure; subcutaneous injection can cause tissue necrosis.

Oral suspension

Route: Oral

Strengths: 50 mg/5 mL

Injection

Route: Parenteral

Strengths: 30 mg/mL, 60 mg/mL, 200 mg/mL