PHENOBARBITAL

Mechanism of Action :


Phenobarbitone is a short-acting barbiturate. It depresses the sensory cortex, reduces motor activity, changes cerebellar function, and produces drowsiness, sedation and hypnosis. Its anticonvulsant property is exhibited at high doses.
Onset: Hypnosis: Oral: 20-60 min; IV: Approx 5 min.
Duration: Oral: 6-10 hr; IV: 4-10 hr.

Indication, Dosage and Frequency :

Oral
PARTIAL SEIZURES
Adult: 60-180 mg daily taken at night. Titrate dose according to patient's needs to achieve adequate control of seizures. Plasma concentrations of 15-40 mcg/ml (65-170 micromol/l) are usually required.
Child: 1 mth-12 yr: Initially, 1-1.5 mg/kg bid. Increase by 2 mg/kg daily, as required, to a maintenance dose of 2.5-4 mg/kg once or bid. 12-18 yr: Initially, 60-180 mg bid. Maintenance: 60-180 mg once daily.
GENERALISED TONIC-CLONIC SEIZURES
Adult: 60-180 mg daily taken at night. Titrate dose according to patient's needs to achieve adequate control of seizures. Plasma concentrations of 15-40 mcg/ml (65-170 micromol/l) are usually required.
Child: 1 mth-12 yr: Initially, 1-1.5 mg/kg bid. Increase by 2 mg/kg daily, as required, to a maintenance dose of 2.5-4 mg/kg once or bid. 12-18 yr: Initially, 60-180 mg bid. Maintenance: 60-180 mg once daily.
SEDATION
Adult: 30-120 mg/day in 2-3 divided doses.
Child: 6 mg/kg/day or 180 mg/m2/day divided in 3 equal doses.
HYPNOTIC
Adult: 100-320 mg at bedtime. Do not admin for >2 wk for the treatment of insomnia.
PRE-OPERATIVE SEDATION
Child: 1-3 mg/kg 1-1.5 hr before procedure.
Intravenous
STATUS EPILEPTICUS
Adult: Doses of 10 mg/kg to a max of 1 g.
Child: As sodium: Neonates and children up to 12 yr: Initially, 20 mg/kg by slow IV inj then 2.5-5 mg/kg once or bid. 12-18 yr: Initially 20 mg/kg (max 1 g) by slow IV inj then 300 mg bid.
GENERALISED TONIC-CLONIC SEIZURES
Child: As sodium: Neonates: Loading dose is 20 mg/kg by slow IV inj followed by 2.5-5 mg/kg once daily either by slow IV inj or orally.
PARTIAL SEIZURES
Child: As sodium: Neonates: Loading dose is 20 mg/kg by slow IV inj followed by 2.5-5 mg/kg once daily either by slow IV inj or orally.
PRE-OPERATIVE SEDATION
Child: As sodium: 1-3 mg/kg 1-1.5 hr before procedure.
Intramuscular
EMERGENCY MANAGEMENT OF ACUTE SEIZURES
Adult: As sodium: 200 mg IM repeated after 6 hr if necessary.
Child: As sodium: 15 mg/kg IM as a single dose.
SEDATION
Adult: As sodium: 30-120 mg/day in 2-3 divided doses.
PRE-OPERATIVE SEDATION
Adult: As sodium: 100-200 mg 1-1.5 hr be

Interactions :

May enhance the hepatotoxic potential of paracetemaol overdoses. May decrease levels/effects of various CYP isoenzyme substrates e.g. teniposide, methotrexate, antipsychotics, β-blockers, calcium-channel blockers, other anticonvulsants, chloramphenicol, cimetidine, corticosteroids, ciclosporin, doxycycline, oestrogens, felbamate, griseofulvin, tacrolimus, furosemide, methadone, oral contraceptives, theophylline, TCAs, warfarin. May reduce effects of guanfacine. Reduced metabolism and or increased toxicity with chloramphenicol, felbamate, MAOIs, valproic acid. May enhance the nephrotoxic effects of methoxyflurane.
Evening primrose may reduce seizure threshold. Increased CNS depression may occur with valerian, St John's wort, kava kava, gotu kol