Phenobarbital = PB oral

Therapeutic action

Antiseizure (antiepileptic), sedative.

Indications

Epilepsy: generalised tonic-clonic seizures and focal (partial) seizures.

Forms and strengths

• 60 mg tablet.

Dose

Start with a low dose then increase gradually based on the patient's response and tolerance.

Due to the numerous and potentially severe adverse effects of PB, patients should be kept under close surveillance.

• Child 1 month to 11 years: start with 2 to 3 mg/kg once daily at bedtime or 1 to 1.5 mg/kg 2 times daily for 2 weeks; increase the daily dose by 1 to 2 mg/kg every week, up to 2 to 6 mg/kg once daily if necessary.
• Child 12 years and over and adult: start with 1 mg/kg, maximum 60 mg, once daily at bedtime for 2 weeks; increase the daily dose by 15 to 30 mg every week, up to 3 mg/kg once daily if needed, maximum 180 mg daily.

Duration

As long as required. Do not stop treatment abruptly, even if changing to another antiseizure medication.

Contra-indications, adverse effects, precautions

• Do not administer to patients with severe impairment of respiratory, renal, or hepatic function because of the risk of accumulation.
• Administer with caution in children, older patients, and patients with mild to moderate impairment of respiratory, renal, or hepatic function.
• May cause drowsiness, dizziness, headache, behavioural disturbances, respiratory depression, hypotension, vitamin D deficiency, osteoporosis, haematologic disorders, gastrointestinal disturbances, and rarely severe hypersensitivity reactions including Stevens-Johnson, Lyell, and DRESS syndromes.
• Early symptoms such as fever, rash, mouth ulcers, and bleeding require immediate medical attention.
• Avoid or monitor combination with mefloquine, drugs containing alcohol, benzodiazepines, opioid analgesics, antipsychotics, first-generation antihistamines, antidepressants, and other antiseizure medications.
• Use with extreme caution with benzodiazepines and opioid analgesics because of the increased risk of respiratory depression.
• PB may reduce the effect of many drugs including diazepam, midazolam, antimicrobials, some antiretrovirals, corticosteroids, tricyclic antidepressants, itraconazole, direct-acting antivirals for chronic hepatitis C, and warfarin. Adjust dosage if necessary.
• For implants and oral contraceptives, use injectable medroxyprogesterone or an intrauterine device.
• Avoid alcohol during treatment.
• Pregnancy: avoid because of the risk of facial and cardiac malformations, hypospadias, and small size for gestational age. If PB is the only option, use the lowest effective dose and administer folic acid 5 mg daily during the first trimester starting as early as possible.
• PB plasma concentrations may decrease during pregnancy. Monitor clinical response, increase dose if needed, then resume the usual dose after delivery. Monitor the child for a few days.
• Breast-feeding: administer with caution, reduce the dose if increased during pregnancy, and monitor the child for drowsiness, lethargy, and poor feeding.
• PB is not recommended for absence seizures because symptoms may worsen.