Resolution of nephrolithiasis in a feline with history of FIP infection treated with GS-441524

What are nephroliths?

Commonly referred to as kidney stones, nephroliths are deposits of minerals located in the kidneys, usually made of insoluble calcium compounds such as calcium oxalate (CaOx).

Recently, the Minnesota Urolith center had found stones comprised of the antiviral GS-441524 in 3 cats that were treated for Feline Infectious peritonitis (FIP),¹ showing that poorly soluble drugs are candidates for forming stones in the kidneys of cats.

Case presentation:

Charlie is a 13-year-old neutered male domestic short hair (DSH) feline, with history of ocular and wet FIP, HCM (hypertrophic cardiomyopathy), periodontal disease and primary GI disease (Inflammatory Bowel Disease, IBD). In January 2021, a month after treatment with GS-441524 was terminated, an abdominal ultrasound revealed a 2.8mm nephrolith in a left calyx of the kidney.

Over the subsequent 18 months, Charlie received treatment for GI disease with prednisolone 5mg a day and subsequently with Chlorambucil 2mg every other day, in addition to Revitalize Health and Immunity, from Bloom Bioscience. X-ray and abdominal ultrasound performed in July 2022 revealed mild bilateral renomegaly and bilateral nephrolithiasis.

To address the nephroliths, Revitalize Hydration supplementation (a 2.3g premeasured mineral and electrolyte packet mixed with 1-liter of filtered/bottled drinking water) was introduced in place of Charlie’s regular drinking water (bottled water). A follow-up x-ray in April 2023 revealed normal sized kidneys with smooth margins with no nephroliths detected.

Conclusions:

Prevention and non-surgical treatment of nephroliths usually consist of:  Increased hydration –

decreased oxalate and calcium consumption, and administration of potassium citrate.²

Potassium citrate increases urinary citrate levels and binds to calcium in the urine, preventing CaOx complex formation. ³ Citrate is also utilized to improve the solubility of poorly soluble drugs.⁴

The nature of the nephroliths found in Charlie’s kidneys was not investigated as the condition was not severe to require surgical intervention. However, increased hydration and supplementation with electrolytes and buffering agents contained in Revitalize Hydration may have contributed to resolution of the nephrolithiasis that previously persisted for 2 years.

1. https://vetmed.umn.edu/urolith-center/image-of-month/mysterious-new-stone-type-cats
2. Alford, E. Furrow, M. Borofsky, J. Lulich J. Animal models of naturally-occurring stone disease. Nat. rev. Urol. 17 (2020) 691-705.
3. Lulick, A. C. Berent, L. G. Adams, J. L. Westropp, J. W. Bartges, C. A. Osborne. ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats. J. Vet. Intern. Med. 30 (2016) 1564–1574.
4. Sareen, G. Mathew, L. Joseph. Improvement in solubility of poor water-soluble drugs by solid dispersion. Int. J. Pharm. Investig. 2 (2012) 12-17.