Time   total free bound f/b ratio % free % bound Pre mean 28.1 11.2 16.9 0.7 39.8 60.2 SD 0.6 0.3 0.5 0.0 0.6 0.6 Post Sulfa mean 28.0 14.0* 14.0* 1.0* 49.9* 50.1* SD 0.5 0.3 0.3 0.0 0.3 0.3

Table 2: Phenobarbital levels in normal dogs on oral phenobarbital before and 1 hour after IV sulfadimethozine administration (15 mg/kg). Levels are expressed in μg/ml for total, free and protein-bound phenobarbital serum levels. Samples were taken 2 and 3 hours following administration of 4 mg/kg of phenobarbital. Data are as mean and standard deviation (n=5). While the total phenobarbital levels are not statistically significant, all other measures were significantly different (p<0.05*, student's paired t-test).