Affymax climbed 19 percent to $6.26 at 4 p.m. New York time in the biggest gain since August 2010. The drug, peginesatide, is ¡°non-inferior¡± to Amgen¡¯s Epogen and Aranesp and J&J¡¯s Procrit, Food and Drug Administration staff evaluating whether the product should be approved for sale said in a report today.

Peginesatide would be the first marketed therapy for Palo Alto, California-based Affymax, competing with drugs such as Epogen, which generated 2010 sales of $2.5 billion. FDA reviewers also said the medicine is as safe as Epogen and Procrit for people on dialysis, the patient group for whom Affymax seeks approval. An advisory panel will meet Dec. 7 to evaluate the drug.

¡°We believe the probability of approval for the dialysis indication is high and that the FDA may have left the door open to approval¡± for chronic kidney disease patients who aren¡¯t on dialysis, William Tanner, an analyst with Lazard Capital Markets in New York, said today in a note to clients after reviewing the FDA staff report.

The effects of peginesatide last longer, making it more convenient and less expensive, according to Affymax¡¯s September quarterly report. The drug can be injected once a month, compared with an initial dose of three times weekly for Epogen.