Pharmacokinetics of Phenazopyridine in Healthy Goats at Two Different Dosing Regimens

Abstract:

Background: Obstructive urolithiasis is one of the most frequent small ruminant emergencies. Because of the possibility of renal compromise, non-steroidal anti-inflammatories are sometimes contraindicated for analgesia. Phenazopyridine, a urinary bladder analgesic, may be an alternative. Hypothesis/

Objective: The objective was to investigate the pharmacokinetics of orally administered phenazopyridine. We hypothesized that the phenazopyridine concentration in the plasma and urine will be increased in the 8 mg/kg every 12-hour dosing regimen when compared to 4 mg/kg every 8 hours. Animals: Six male intact Boer goats were used (8-9 months old). They were deemed healthy based on physical examination and blood work.

Methods: The goats were administered 4 mg/kg of phenazopyridine orally every 8 hours; blood and urine was collected. After a 7 day wash out period, the goats were orally dosed with 8 mg/kg of phenazopyridine every 12 hours. Blood and urine were collected at pre-determined time points. Phenazopyridine concentrations were assessed by high performance liquid chromatography with UV detection.

Results: All of the goats did well during the study. There was no phenazopyridine detected in the urine. In the plasma, phenazopyridine was only detected at 8 hours (4 mg/kg dosing group) and at 12 hours (8 mg/kg dosing group). Conclusions and Clinical Importance: The pharmacokinetics of phenazopyridine have been elucidated, but phenazopyridine is not well absorbed or excreted in the urine. There appears to be no adverse effects, but the efficacy remains unclear. The metabolites of phenazopyridine may be responsible for any analgesic effect, but this still needs to be characterized.