Relationship between serum and brain concentrations of phenytoin in the dog.

The concentrations of phenytoin (DPH) in the CNS of adult dogs given the drug by IV injection, continuous IV infusion, or repeated daily oral administration and of newborn pups given DPH by IV injection were consistently proportional to serum concentrations of the drug at the time of blood sample collections. Adult dogs injected IV with [14C]DPH failed to show predilection of the drug for the 13 anatomic brain sections sampled. The pharmacokinetics of DPH were studied in adult and neonatal dogs given 15 mg of the drug/kg of body weight as a single IV injection. The mean half-life of the drug in adult dogs injected IV was 4.5 hours. The serum half-life of injected DPH was lowest in pups 30 days of age when compared with that in other age groups. The serum half-life of injected DPH was increased in adult dogs under pentobarbital anesthesia.