Probenecid was tested as a way to reduce the massive water loss caused by tolvaptan, potentially making the only approved PKD drug more tolerable for patients.
Background
Tolvaptan (Jynarque) is the only FDA-approved treatment for ADPKD, but it has a major tolerability problem: it blocks vasopressin receptors in the kidney collecting ducts, causing patients to produce 4–8 liters of urine daily. Many patients discontinue treatment because of this burden. Mayo Clinic researchers hypothesized that probenecid — a cheap gout drug that blocks renal organic anion transporters — could reduce this polyuria by altering tolvaptan's renal handling.
How It Works
Probenecid inhibits organic anion transporters (OAT1/OAT3) in the kidney proximal tubule. The hypothesis was that blocking these transporters would reduce tolvaptan's access to its target (V2 receptors in collecting ducts) or alter its metabolite excretion, thereby maintaining the cyst-inhibiting effect while reducing the water loss side effect. This is a pharmacokinetic optimization approach rather than a new therapeutic target.
Clinical Trial Details
The Phase 2 study (NCT05190744) enrolled 36 ADPKD patients already on tolvaptan at Mayo Clinic. It measured urine osmolality and volume with and without probenecid co-administration. The study was completed in 2024 with Otsuka America (maker of tolvaptan) as a collaborator. Results have not been widely published.
Why It's Promising
If probenecid reduces tolvaptan-induced polyuria without reducing efficacy, it could dramatically improve quality of life for the thousands of patients on tolvaptan. Both drugs are generic and cheap.
Limitations & Concerns
Study completed but results not widely published — silence after completion sometimes indicates negative results. Probenecid has its own side effects (kidney stones, GI issues). This doesn't treat PKD itself, only a side effect of the current treatment.