Pharmacokinetics of pentobarbital in the dog

The pharmacokinetics of pentobarbital were studied after i.v. administration of a 30-mg/kg dose to five dogs. Pentobarbital plasma concentrations were measured with a new gas chromatographic method, utilizing on-column methylation of pentobarbital and as a butabarbital internal standard. The kinetics of pentobarbital distribution and elimination were analyzed with a three-compartment open mammillary model. The elimination-phase half-life of pentobarbital was 8.2 +/- 2.2 hr. The steady-state volume of pentobarbital distribution was 1.08 +/- 0.21 liters/kg and the elimination clearance was 0.0013 +/- 0.0004 liters/min X kg. Threshold pentobarbital concentrations required to suppress the corneal reflex and withdrawal response to pain were 26.4 +/- 4.6 and 23.0 +/- 2.9 micrograms/ml, respectively. These results should facilitate the design of i.v. anesthetic regimens with pentobarbital.