Salivary excretion of 5-fluorouracil. II. Fluctuation of saliva/plasma concentration ratio and salivary clearance during a constant rate intravenous infusion in beagle dogs.

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Abstract
Salivary excretion of 5-fluorouracil (5-FU) was investigated during constant rate intravenous infusion (0.306 mg/kg/min) in three male beagle dogs. Parotid (Pr) and mandibular-sublingual (MS) saliva were collected separately by stimulating salivation with 10% citric acid. After the start of 5-FU infusion, plasma and salivary 5-FU concentration increased rapidly to approach their steady state leveles. There was a significant correlation between each saliva and plasma 5-FU concentration (p < 0.01). The saliva/plasma drug concentration ratio (S/P ratio) and salivary pH were significantly higher in Pr than in MS saliva (p < 0.001), similar to the results following bolus intravenous administration of 5-FU in beagle dogs. Both S/P ratio and salivary clearance increased with time before steady state. Thereafter, these values approached almost constant levels and their flucutations became smaller than those following the bolus intravenous administration. These results showing S/P ratio and salivary clearance of 5-FU were affected by the plasma drug concentration, suggested the possibility that non-linear pharmacokinetics may be involved in the salivary excretion of 5-FU.