Pharmacokinetics of Uridine Following Ocular, Oral and Intravenous Administration in Rabbits

The pyrimidine nucleoside uridine has recently been reported to have a protective effect on cultured human corneal epithelial cells, in an animal model of dry eye and in patients. In this study, we investigate the pharmacokinetic profile of uridine in rabbits, following topical ocular (8 mg/eye), oral (450 mg/kg) and intravenous (100 mg/kg) administration. Blood and urine samples were serially taken, and uridine was measured by high-performance liquid chromatography-tandem mass spectrometry. No symptoms were noted in the animals after uridine treatment. Uridine was not detected in either plasma or urine after topical ocular administration, indicating no systemic exposure to uridine with this treatment route. Following a single intravenous dose, the plasma concentration of uridine showed a bi-exponential decay, with a rapid decline over 10 min, followed by a slow decay with a terminal half-life of $0.36{\pm}0.05$ h. Clearance and volume of distribution were $1.8{\pm}0.6$ L/h/kg and $0.58{\pm}0.32$ L/kg, respectively. The area under the plasma concentration-time curves (AUC) was $59.7{\pm}18.2{\mu}g{\cdot}hr/ml$, and urinary excretion up to 12 hr was ~7.7% of the dose. Plasma uridine reached a peak of $25.8{\pm}4.1{\mu}g/ml$ at $2.3{\pm}0.8$ hr after oral administration. The AUC was $79.0{\pm}13.9{\mu}g{\cdot}hr/ml$, representing ~29.4% of absolute bioavailability. About 1% of the oral dose was excreted in the urine. These results should prove useful in the design of future clinical and nonclinical studies conducted with uridine.