Effects of phenylbutazone, firocoxib, and dipyrone on the diuretic response to furosemide in horses.
Authors: White Julianne M, Colbath Aimee C, Schott Harold C
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Phenylbutazone's well-documented interference with furosemide efficacy has long concerned practitioners managing horses requiring concurrent diuretic and anti-inflammatory therapy, yet whether selective COX-2 inhibitors or atypical NSAIDs offered a safer alternative remained unclear. White and colleagues conducted a prospective crossover study in eight healthy mares, administering each animal four different treatment protocols—furosemide alone, or furosemide combined with phenylbutazone, firocoxib, or dipyrone—with continuous urine collection via ureteral catheters for four hours post-injection. All three NSAIDs reduced furosemide-induced diuresis by approximately 25% compared to furosemide monotherapy (producing 19.1–19.1 mL/kg versus 23.4 mL/kg urine output respectively), with no statistically significant differences between the drug classes despite firocoxib trending slightly lower. The findings suggest that switching from phenylbutazone to a COX-2 selective agent or dipyrone offers minimal advantage in preserving diuretic response or potentially mitigating nephrotoxic risk—a critical consideration for equine professionals balancing pain management against the renal consequences of reduced furosemide clearance during colic or other conditions requiring both therapies.
Read the full abstract on PubMed
Practical Takeaways
- •All commonly used NSAIDs in horses reduce furosemide's diuretic effectiveness by ~25%; consider timing NSAID administration away from furosemide therapy if diuresis is clinically critical
- •Switching from phenylbutazone to firocoxib or dipyrone will not improve furosemide response—choice should be based on other factors (GI safety, individual response) rather than diuretic compatibility
- •Monitor individual horses for variable responses to furosemide when NSAIDs are co-administered; some animals may show greater or lesser reduction in urine output
Key Findings
- •All three NSAIDs (phenylbutazone, firocoxib, and dipyrone) reduced furosemide-induced 4-hour urine volume by approximately 25% compared to furosemide alone (23.4 mL/kg vs 17.7–19.1 mL/kg, P<0.001)
- •No significant differences in diuretic response reduction were observed between phenylbutazone (19.1 mL/kg), firocoxib (17.7 mL/kg), or dipyrone (19.1 mL/kg) pretreatment groups
- •Interindividual variability in furosemide diuresis response after different NSAID pretreatments was noted among study subjects
- •COX-2 selective inhibitors and atypical NSAIDs offer no clinically meaningful advantage over nonselective NSAIDs regarding effects on furosemide efficacy or potential nephrotoxicity risk