Affymax Shares Climb As FDA Considers Wider Use for Anemia Drug

[Corrected: 3:48 pm, 12/7/11] Investors have had pretty low expectations about the prospects for Affymax’s anemia drug, which seeks to challenge Amgen’s 22-year monopoly in the field. But the expectations are starting to rise today, as Affymax approaches its make-or-break moment.

Palo Alto, CA-based Affymax (NASDAQ: AFFY) saw its shares rise more than 20 percent this morning after staff from the FDA posted online briefing documents in advance of an advisory committee on Wednesday. The staff comments were made about peginesatide, an experimental anemia drug Affymax and its partner Takeda Pharmaceuticals hope to market to patients on kidney dialysis. The shares climbed to $6.34, up about 20 percent, at 10:19 am Eastern time.

Many investors wrote off Affymax in June 2010, when the company announced the results from a quartet of pivotal clinical trials that enrolled 2,600 patients. The studies showed that kidney patients who aren’t yet on dialysis had an increased rate of heart-related serious adverse events, such as heart attack, stroke, congestive heart failure, and death, when they got the Affymax drug instead of the usual Amgen treatment. About 21.6 percent of patients on the Affymax drug had those serious adverse events, compared with 17.4 percent on the Amgen drug.

Affymax, however, went ahead with its application to the FDA, saying the safety profile of its drug appeared similar to the Amgen drug in the sicker population of kidney dialysis patients. Today’s FDA document raises the safety concern about the Affymax drug, but does so in a balanced way that provides some context about well-known safety issues with Amgen’s drug as well. The FDA noted that while Affymax’s drug appeared worse “numerically” in the pre-dialysis population, there wasn’t a statistically significant difference between it and the Amgen drug.

The FDA also noted that despite efforts to randomly assign patients to one drug or the other in the trial, patients who were sicker at the start ended up getting the Affymax drug, putting it at a disadvantage.

Given that context, the FDA staff said it plans to ask the advisory committee not just for its opinion about Affymax’s drug for dialysis patients, but for the potentially larger group of patients that have chronic kidney disease that doesn’t yet require dialysis.

“FDA is asking the committee’s advice about the benefit risk profile of peginesatide for patients with CKD [chronic kidney disease], given the safety findings and in light of the prior history with agents that stimulate the erythropoietin receptor,” the FDA staff said.

FDA briefing documents can often be harsh toward new products, but the early read of the Affymax documents was positive on Wall Street. “We believe the probability of approval for the dialysis indication is high and that the FDA may have left the door open to approval” in the pre-dialysis population, said William Tanner, an analyst with Lazard Capital Markets, in a note to clients this morning. His comment was reported earlier today by Bloomberg News.

The FDA’s Oncologic Drugs Advisory Committee will review the evidence presented by regulators and Affymax at a meeting on Wednesday. [Corrected FDA deadline] The FDA has a deadline of March 27 to make its decision on whether to allow the Affymax drug on the U.S. market.

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