Long-acting barbiturate — GABA-A receptor positive allosteric modulator (binds different site than benzodiazepines). Anticonvulsant + sedative. Strong CYP3A4 / CYP2B6 / UGT inducer — major DDI source. Largely replaced by safer antiseizure agents but still used in resource-limited settings + neonatal seizures.
Half-Life (t½)
PO: 96h, IV: 96h, IM: 96h
Dosing Guidelines
PO: Typical 100 mg (Range: 30–300 mg)
Target Organ Systems
nervous
digestive
Interactions
Theophylline (caution): CYP1A2 induction. Landay 1978 (PMID:659737) verbatim: "Following four weeks of phenobarbital administration, all six subjects showed a resultant increase in serum clearance varying from 11% to 60% with a mean increase of 34% (from 3.01 to 4.04 L/hr/1.73 M2)". 6 healthy nonsmoking adults, within-subject before/after design. CL × 1.34 → induction_factor 1.34. Clinically: barbiturate co-administration with asthma therapy requires theophylline dose adjustment.