Phenobarbital
Phenobarbital. Long-acting barbiturate — GABA-A receptor positive allosteric modulator (binds different site than benzodiazepines).… Oral half-life 5.1 d.
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.
PK: the stored 96 h on all three routes is stated by NEITHER cited paper and is not a neonatal figure either — the adult values are 139 h intravenously and 122 h orally (PMID:7068937, verbatim "the mean elimination half-life was 5.8 days" and "averaged 5.1 days for the oral dose") and about 90 h intramuscularly (PMID:624773). Each route now carries its own. V 42 L is retained: it is 0.60 L/kg scaled to 70 kg and, being measured after intravenous dosing, is a TRUE volume that pairs safely with a bioavailability. F 0.949 is verbatim ("94.9 per cent"). The intramuscular F of 0.76 was a CROSS-PAPER PRODUCT, 0.80 relative to oral multiplied by 0.949 absolute, and is dropped. Both absorption rates dropped as unstated.
Pharmacokinetics
- Oral — t½ 5.1 d · F 95% · Vd 42 L
- IV — t½ 5.8 d · F 100% · Vd 42 L
- Intramuscular — t½ 3.8 d
Related compounds
- Theophylline — caution
Sources: PMID:7068937, PMID:659737, PMID:624773