Phenobarbital

Chemical

Barbituric acid

Use

Tx epilepsy (except Petit Mal)

Presentation

Tablets

IV 200mg/mL

Dose

60 – 80mg nocte

Route

PO/IV

Onset

CNS levels peak 1 – 3hrs

MoA (mechanism)

  • ↑Cl– flux of GABAA receptors
  • ∴ hyperpolarising & ↓ excitability
  • ↑ seizure threshold
  • Also directly blocks glutamate (exit) signalling

PD

CNS – anticonvulsant, sedative

PK

A

OBA 90%

D

PPB 40%

Very low

M

Hepatic hydroxylation & glucuronidation

E

Metabolites via kidneys

*** one of the longest acting barbiturates

t ½ B up to 7 days