In a letter released Wednesday, the Food and Drug Administration rebuked Seattle-based ZymoGenetics for suggesting in a news release that its first product, Recothrom, is safer than a rival treatment because patients are less likely to develop antibodies against the product.

(Read the letter here).

ZymoGenetics has claimed repeatedly that Recothrom, a synthetic protein designed to stop bleeding during surgery, avoids complications associated with another treatment manufactured by King Pharmaceuticals, which is derived from cows. King's product is sold with a "black box" warning regarding the potential for abnormalities, including severe bleeding.

In its January 17 news release announcing that the FDA had approved Recothrom, ZymoGenetics said, "A Phase 3 pivotal clinical trial showed that RECOTHROM had comparable efficacy and a significantly lower incidence of antibody formation compared to the commercially available bovine thrombin product."

But an FDA official wrote in an April 25 letter to ZymoGenetics' associate director of regulatory affairs that the statement was "false or misleading."

"This statement is false or misleading because it suggests that Recothrom is safer than the bovine thrombin product due to a lower incidence of antibody formation in the patients who took the Recothrom. However, this statement excludes important contextual information necessary to understand the limitation of this finding."

The letter continues, "The development of antibodies in either group did not lead to any adverse events such as excessive bleeding. In addition 5 the incidences of pre-specified adverse events were similar between Recothrom and bovine thrombin."

Susan Specht, a spokeswoman for ZymoGenetics, said that the company's statement about the phase three trial was correct.

"It was correct in that in the Phase 3 three trial we did see that. We did see significantly lower incidence of antibody formations. You would have to ask the FDA why they were concerned," she said.

However, Specht said that ZymoGenetics had added a footnote to the release on its Web site.

The footnote states, "In the Phase 3 pivotal clinical study comparing RECOTHROM to bovine thrombin, adverse events were reported with similar frequency in both treatment groups. No reported adverse events were considered causally related to antibody formation in either group."

(Read the updated press release here).

Specht said that ZymoGenetics has responded to the FDA's letter but has not received a response.

She said the FDA's letter would not "hamper our efforts to sell Recothrom at all," since it does not have an impact on Recothrom's packaging or marketing material. On Wednesday, ZymoGenetics said that Recothrom brought in nearly $1 million of sales during its first two months on the market.

(Read my post on the sales figures here).

"Look at our package insert. Look at the cattle plasma package insert. When you compare, you can see that there are advantages to ours," she said.

Analysts said that letters such as the one delivered to ZymoGenetics were fairly common, especially after a new drug comes to market.

David Miller, the president of Biotech Stock Research in Seattle, said that the ZymoGenetics letter would have been more concerning if it involved ZymoGenetics' marketing materials, since the company would probably have had to recall those materials.

Kevin DeGeeter, an analyst at Oppenhimer & Co., said he did not think the letter would be "material" to Recothrom's sales. However, DeGeeter, who has said it will be difficult for
ZymoGenetics to rapidly capture market share from King, said "the lack of hard head-to-head clinical data linking higher antibody levels with more adverse events – is one of the central reasons we expect the transition to be slower than management expects."