Phenobarbital sodium
Related Subjects:
|Status Epilepticus (Epilepsy)
|Coma management
|Lorazepam
|Phenytoin
|Levetiracetam
|Epilepsy - General Management
|First Seizure
|Epilepsy in Pregnancy
|Febrile seizures
- Also known as phenobarbitone or phenobarbital.
- A long-acting barbiturate with both hypnotic and anticonvulsant properties.
โ๏ธ Mode of Action
- Enhances the activity of GABA (ฮณ-aminobutyric acid), the main inhibitory neurotransmitter in the CNS.
- Increases the duration of chloride channel opening at the GABA-A receptor, leading to neuronal hyperpolarisation and reduced excitability.
- Also reduces glutamate-mediated excitatory transmission.
๐ฉบ Indications & Dosing
- ๐ Epilepsy (specialist use, not 1st line): 60โ180 mg PO nocte.
- ๐จ Status epilepticus: Dilute 1 in 10 with water for injections.
Dose: 10 mg/kg IV at a rate โค100 mg/min.
โ ๏ธ Max dose = 1 g.
๐ Interactions
- Potent inducer of hepatic microsomal enzymes (CYP450) โ reduces levels of many drugs (e.g., warfarin, steroids, ciclosporin, other anticonvulsants).
- Can reduce the efficacy of oral contraceptives.
- โ Breastfeeding is not recommended due to drug excretion in breast milk.
โ ๏ธ Cautions
- Avoid concurrent use with other CNS depressants (e.g., alcohol, opioids, benzodiazepines) โ risk of severe sedation or respiratory depression.
- Monitor bone health in long-term use (risk of osteoporosis/osteopenia).
โ Contraindications
- Hypersensitivity to barbiturates.
- Severe respiratory depression.
- Acute intermittent porphyria.
- Severe renal or hepatic impairment.
โ ๏ธ Side Effects
- ๐ Haematological: Megaloblastic anaemia (folate deficiency), aplastic anaemia (rare).
- ๐ฆด Musculoskeletal: Osteopenia, osteoporosis, osteomalacia, hypocalcaemia, Dupuytrenโs contracture.
- ๐ง CNS: Drowsiness, lethargy, ataxia, nystagmus, confusion, cognitive impairment, depression.
Paradoxical agitation/excitement in elderly or children.
- ๐ก๏ธ Rare but severe: Toxic epidermal necrolysis, hepatitis, cholestasis.
๐ก Clinical Pearls
- ๐ Rarely first-line in the UK due to cognitive side effects, risk of dependence, and strong CYP450 induction leading to drug interactions.
- ๐ Still widely used in low-resource settings as it is cheap, effective, and available for epilepsy management.
- ๐ถ Occasionally used in neonatal seizures when other agents fail.
- ๐ Remains important in status epilepticus protocols (after benzodiazepines, phenytoin/levetiracetam) in some guidelines.
- ๐ง Understanding its mechanism helps appreciate how newer antiepileptics were designed to improve safety and tolerability.
๐ References
