PHENOBARBITAL = PB oral

Therapeutic action

• Antiseizure (antiepileptic), sedative

Indications

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

Forms and strengths

• 60 mg tablet

Dosage

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

• 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 increments of 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 (max. 60 mg) once daily at bedtime for 2 weeks; increase the daily dose by increments of 15 to 30 mg every week, up to 3 mg/kg once daily if needed (max. 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 (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 (caution when driving/operating machinery), dizziness, headache, behavioural disturbances;
  • respiratory depression, hypotension;
  • vitamin D deficiency (consider supplementation), osteoporosis, haematologic disorders, gastrointestinal disturbances;
  • rarely: hypersensitivity reactions (including severe cutaneous reactions such as Stevens-Johnson, Lyell and DRESS syndromes). In these cases, stop treatment. Early symptoms such as fever, rash, mouth ulcers and bleeding require immediate medical attention.
• Avoid or monitor the combination with: 
  • mefloquine (reduced effect of PB);
  • drugs containing alcohol, benzodiazepines, opioid analgesics, antipsychotics, first-generation antihistamines (hydroxyzine, promethazine), antidepressants, other antiseizure medications, etc. (increased sedation).
• Use with extreme caution with benzodiazepines and opioid analgesics (increased risk of respiratory depression).
• PB may reduce the effect of many drugs:
  • diazepam, midazolam, antimicrobials, some antiretrovirals, corticosteroids, tricyclic antidepressants, itraconazole, direct-acting antivirals for chronic hepatitis C, warfarin, etc. Adjust dosage if necessary.
  • implants and oral contraceptives: use injectable medroxyprogesterone or an intrauterine device.
• Avoid alcohol during treatment (increased risk of adverse effects).
• Pregnancy: avoid (risk of facial and cardiac malformations, hypospadias, small for gestational age). 
  • In case of pregnancy during treatment, prefer a safer drug (levetiracetam). If PB is the only option, provide counselling about the risks to the child; use the lowest effective dose.
  • Administer folic acid high dose (5 mg daily) during the first trimester. Start as soon as possible, including during the preconception period in case of planned pregnancy.
  • 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 (risk of accumulation and drowsiness or withdrawal symptoms). 
• Breast-feeding: administer with caution (excreted in milk); reduce the dose if increased during pregnancy and monitor the child (risk of drowsiness, lethargy and poor feeding). 

Remarks

• PB is subject to international controls: follow national regulations.
• PB is not recommended for absence seizures (risk of worsening symptoms).
• Plasma concentrations are stable after 2 to 3 weeks. Caution: risk of accumulation. 
• Also comes in 15 mg and 30 mg tablets.

Storage