What are the key pharmacological characteristics of phenobarbital?

Phenobarbital is an old antiseizure medicine with specific mechanisms of action, bioavailability, distribution, and elimination pathways.

Mechanism of action: Potentiation of GABA(A) receptor-mediated inhibition by prolonging periods of Cl channel opening; inhibition of AMPA-ergic glutamate receptors; at high doses, inhibition of rapid-firing voltage-gated Na-channels.
Bioavailability: Intravenous: 100%; Intramuscular: 101 ± 11%.
Time to peak after single dose: Intravenous: 12 to 60 minutes; Intramuscular: 2-8 hours.
Volume of distribution: Neonates and young infants: 0.8-1.0 L/kg; Adults: 0.42-0.73 L/kg.
Main routes of elimination: 9-33% (average 23%) of the dose is excreted unchanged in urine. The remainder undergoes hepatic N-glucosidation and oxidation (CYP2C9 with a minor role of CYP2C19 and CYP2E1) followed by conjugation.
Elimination half-life (hours): Neonates: 43-217; Infants (1-12 months): 63.2+4.2; Children: 37-198; Adults: 75-126.
Plasma clearance (mL/h/kg): Neonates: 2.7-10.7; Children: 5.3-11.3; Adults: 2.1-4.9.
Protein binding: 45-60%.
Active metabolites: None.