Travere Therapeutics just misses on confirmatory study for kidney disease drug, stock plummets

Travere Therapeutics’ kidney disease drug narrowly failed its confirmatory study seven months after it won accelerated approval.

Travere said Thursday it still intends to apply for full approval of Filspari in IgA nephropathy in the first half of next year, meaning the FDA will have to weigh the study results and decide whether to pull the drug.

The key endpoint in the Phase III study was a measure of kidney function known as estimated glomerular filtration rate (eGFR) total slope. The smaller the slope, the slower the decline of kidney function. Patients either received Filspari or irbesartan — a generic blood pressure drug used to treat nephropathy. Over 110 weeks, patients who received Filspari saw a smaller change in their eGFR total slope compared to those in the comparator arm. But the difference between the total slopes of the two groups had a p-value of 0.058, just missing statistical significance.

Travere’s shares tumbled 40% on the news Thursday morning.

IgAN is caused by the buildup of an antibody called immunoglobulin A in the kidneys. The kidneys become inflamed, making it more difficult for them to function properly, and that can eventually lead to kidney failure. Travere won accelerated approval in February based on data that suggested Filspari reduced the amount of elevated protein in urine significantly more than irbesartan.

Travere’s drug has been under review in Europe since last August. The company said Thursday that European regulators agreed to a different confirmatory endpoint: eGFR chronic slope. Unlike total slope, which begins measuring at the start of treatment, chronic slope begins at week 6. On that measure, Filspari showed a statistically significant improvement over irbesartan in the data released Thursday.

Travere said it expects an opinion from the EU’s drug review body by the end of this year.

Bill Rote

“We started the study with chronic slope as the primary endpoint, and it was only after extended discussions with the FDA where we were required to shift it to total slope as the primary,” Travere’s head of R&D Bill Rote said during an analyst call Thursday morning.

Filspari’s miss on its confirmatory endpoint was “definitely surprising,” Stifel analyst Alex Thompson wrote in a note Thursday morning.

Analysts said they don’t expect the FDA to pull the drug from the market based on the study results, but they may impact the commercial launch.

“Given the lack of a clear competitive benefit, and data that provides little incentive for payers to prescribe Filspari over irbesartan, we are less certain [of] the market opportunity for Filspari in IgAN and see commercial risk for the product,” William Blair analyst Tim Lugo wrote on Thursday morning.

Travere was founded in 2011 by “Pharma Bro” Martin Shkreli under the name Retrophin, but it rebranded in 2020 to rid itself of those ties.

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