Longitudinal study of phenobarbital in serum, cerebrospinal fluid, and saliva in the dog.

ABSTRACT

Serial assays for phenobarbital were done on the blood serum, cerebrospinal fluid (CSF), and saliva from three epileptic and two clinically normal dogs that were given various oral doses of the drug. In all dogs, the three fluids showed considerable daily fluctuations of phenobarbital concentrations, even after several weeks at the same dosage. The average ratio for CSF/serum was 0.53 and 0.39 for saliva/serum. A highly significant (P less than 0.001) correlation coefficient occurred between CSF and serum (0.95) and between CSF and saliva (0.93); although in some dogs at particular dosages, the CSF and saliva were poorly correlated. Dose-related curves demonstrated a gradually increased phenobarbital concentration in the three fluids up to dosages of 9.0 mg/kg of body weight. The present study suggests that multiple serum or saliva samples should be assayed to account for daily fluctuations; saliva can be a good indicator of unbound phenobarbital concentration in CSF.