The chief executive of Keryx Biopharmaceuticals Inc., Gregory P. Madison, has resigned, the company said Monday, but did not provide a specific reason for his departure.

Madison, who also gave up his seat on the board, had served as CEO of Boston-based Keryx since April 2015, and joined the company the previous year as president and chief operating officer. Keryx is in the Seaport District and develops medicines for kidney diseases.

"On behalf of the entire board, I would like to thank Greg for his contributions to Keryx over the past four years, in particular for his role in transitioning Keryx from a development-stage organization to a commercial entity," Michael Rogers, chairman of the board of directors, said in a news release.


Jodie Morrison, a board member and former CEO of Tokai Pharmaceuticals Inc., will be Keryx's interim chief executive while the company searches for a replacement.

Madison could not be reached for comment. The company's stock closed down 7.3 percent, to $4.43 on the Nasdaq exchange, giving it a market valuation of $528 million.

A company spokeswoman, Amy Sullivan, said that he resigned last Friday and that "there are no improprieties surrounding Greg's resignation."

Reni Benjamin, an analyst with Raymond James & Associates Inc., said he too was reassured by Keryx chief financial officer, Scott A. Holmes, that the resignation "wasn't due to any impropriety. But that's all we know."

Keryx is expecting to report revenue for the first quarter of 2018 of $21 million to $22.5 million, including at least $20 million in net US sales of Auryxia, a kidney disease drug.

"The revenues were in line with analysts' expectations," said Benjamin, who remains bullish on Keryx and believes it will soon top $100 million in annual sales.

The Food and Drug Administration approved Auryxia in 2014 for chronic kidney disease patients on dialysis. Last November, the FDA expanded its use to include the treatment of iron deficiency anemia in patients with chronic kidney disease who weren't on dialysis.


Madison, who holds a business undergraduate degree from the University of Massachusetts Amherst, is a veteran of the biopharma industry. His prior employers include AMAG Pharmaceuticals of Waltham and Genzyme Corp. of Cambridge.

Jonathan Saltzman can be reached at jsaltzman@