Comparative pharmacokinetics of sulfamethazine in plasma and parotid saliva of sheep.

Salivary output in sheep is large enough to be considered a physiologic body fluid compartment. The hypothesis for this work was that pharmacokinetics of sulfamethazine in saliva was similar to that in plasma. A reliable technique was developed to measure parotid salivary output. Mean output of saliva was 3.18 +/- 1.04 L from a single parotid gland per day with a mean flow of 2.21 +/- 0.43 mL/min. Using concentrations of sulfamethazine in parotid saliva made it possible to calculate the total passage of sulfamethazine to parotid saliva, which was calculated to be 3.5% of the total dose. Pharmacokinetic variables obtained for sulfamethazine in plasma and in saliva were closely related (AUC 1408 micrograms.h/mL and AUC 1484 micrograms.h/mL; Vdarea 0.434 L/kg and Vdarea 0.374 L/kg; t 1/2 beta 4.30 h and 3.46 h, respectively) and no substantial differences were observed. The convenience of using salivary concentrations of sulfamethazine for drug monitoring is discussed.