Phenobarbital

Dosage Forms

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Tablets

30 mg

Injection

200 mg/ml

Uses

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Convulsions due to high fever
Grand mal epilepsy
Nodding disease

Dose and Duration

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Convulsions and grand mal epilepsy

Adult: by mouth, 60–180 mg once daily at night.
By IM or SC injection, 50–200 mg as a single dose.
May be repeated after 6 hours if necessary

Child: by mouth, 5–8 mg/kg once daily at night.
By IM injection, 3–5 mg/kg as a single dose

Preparation

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For use as an intravenous injection, dilute the solution with 10 times its volume of water for injections

Contraindications

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Absence seizures (petit mal)

Side Effects

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Drowsiness, sedation
Depression
Movement disorders
Allergic skin reactions
Mood changes
Confusion in the elderly, irritability in children

Interactions

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Alcohol (increased sedation)
Diazepam (increased sedation)
Chlorpheniramine (increased sedation)
Chlorpromazine (increased sedation)
Oral contraceptives (reduced contraceptive effect)
Amitriptyline (anticonvulsant effect cancelled)
Carbamazepine (increased risk of toxicity)
Prednisolone (reduced prednisolone effect)
Warfarin (reduced anticoagulant effect)
Saquinavir, indinavir, lopinavir (reduced plasma concentration of ARVs)

Patient Instructions

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May impair ability to perform skilled tasks, such as driving or operating machinery

Pregnancy

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Do not use in 1ˢᵗ and 3ʳᵈ trimesters

Breast-feeding

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Can be used

⚠️ Caution

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Do not stop treatment abruptly; reduce doses slowly to avoid withdrawal symptoms (uncontrolled seizures)
Identify and treat the underlying cause for convulsions (e.g. malaria, pneumonia, etc.)
Avoid using the injectable phenobarbital when patient has been regularly taking oral phenobarbital to reduce increased risk of side effects
Decreases efficacy of oral contraceptives (advise patient to use another method such as condoms or injectable medroxyprogesterone)
Give vitamin K to new born baby if mother has been taking phenobarbital
Reduce dose in severe liver and kidney disease