Skip to content

Tolfenamic Acid Has a 12-Hour Half-Life in Himalayan Griffons

Himalayan griffon in flight against a blue sky in Shivapuri National Park, Nepal.
Research · Physiology

Tolfenamic acid has an elimination half-life of about 12 hours in Himalayan griffons (Gyps himalayensis), according to an analysis published in 2026. The elimination half-life is the time it takes for the drug concentration in the body to fall by half during elimination; in these vultures it was roughly six times longer than reported in other bird species. The veterinary anti-inflammatory drug was eliminated about as slowly as diclofenac, which is highly toxic to Gyps vultures, but its effects on uric acid were less severe and more reversible.

The researchers reanalysed published results from experiments in which 38 captive vultures received oral doses of 3.2–3.7 mg/kg. Two birds had died during those experiments. The estimated elimination half-life was about 12 hours, and the highest plasma concentration, about 5.7 µg/ml, was reached after roughly 2.1 hours.

Uric acid is the main nitrogenous waste product in birds, and when its concentration becomes high enough, urate crystals can accumulate in tissues as visceral gout. Tolfenamic acid caused a smaller and more reversible rise in uric acid than diclofenac, and the authors found that lethal outcomes occurred only when plasma uric acid exceeded its saturation threshold. They suggest that tolfenamic acid affects the kidneys mainly by altering renal blood flow, rather than by inhibiting uric-acid transport as diclofenac does. This difference may explain why such slow elimination did not produce the same severe toxicity pattern.

Sources and image credit

  1. van der Merwe, P.-H., Mathesh, K., Prakash, V., Siddappa, C. M., & Naidoo, V. (2026). The pharmacokinetics of tolfenamic acid in Himalayan Griffon vultures. A better understanding for the safety of the drug in old world vultures. Environmental Toxicology and Pharmacology, 123, 104977. https://doi.org/10.1016/j.etap.2026.104977Published online 28 February 2026. Pharmacokinetic reanalysis of previously published dosing data from 38 Himalayan griffons.

Image: Shadow Ayush / Wikimedia Commons. Himalayan griffon in Shivapuri National Park, Nepal, 31 January 2021. Representative species photograph, not an experimental bird. Cropped to 16:9. · CC BY-SA 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Physiology

SPECIES IN THIS STORY

Species in this story

Himalayan Griffon Gyps himalayensis Explore species

Independent research and conservation news archive

Did you find this information useful?

Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.

Support Wildlife Vagabond

The news archive will remain freely available.