UPDATE 2-Astellas: U.S. not ready to approve transplant drug

(Adds analyst comment)

By Edwina Gibbs

TOKYO, May 7 (Reuters) - Japan's Astellas Pharma (4503.T) said on Wednesday it would suffer further delays in approval for a new version of its key transplant drug after U.S. authorities said they were not ready to approve it for liver transplants.

Astellas is keen to gain approval for Advagraf, a modified release version of transplant drug Prograf, which brings in some $2 billion in annual sales but lost U.S. patent protection last month.

Advagraf, which is taken once a day, has already been approved in Europe. Prograf is taken twice a day.

Astellas spokesman Takeshi Suda said the U.S. Food and Drug Administration has made a point about the drug's efficacy and safety in its latest action letter but he declined to elaborate.

Receiving an action letter usually means that a drug faces a delay of at least six months before receiving approval.

The FDA declined in January 2007 to approve Advagraf for heart transplants and requested data on kidney and liver transplants.

In March this year it requested further information on Advagraf for kidney transplants.

"I don't think this will come as much of a surprise to the market. If they weren't going to approve it for kidney transplants then they probably weren't going to approve it for liver transplants in the space of a month," said Mizuho Securities analyst Hiroshi Tanaka.

While other drugs can easily lose up to half their sales after a patent ends, doctors and patients dealing with the chances of organ rejection are expected to be reluctant to switch to a generic transplant drug.

Basing their assumptions on slow generic inroads into Novartis's (NOVN.VX) immunosuppressant cyclosporine when it went off patent, most analysts are forecasting annual sales declines of only around 10-15 percent for Prograf.

In a market dominated by Prograf and Novartis's cyclosporine, Prograf commands about 60 percent of the immunosuppressant market for a class of drugs known as calcineurin inhibitors.

In new transplants, its holds market share of around 84 percent for kidney transplants, 90 percent for liver transplants and 63 percent for heart transplants.

Astellas also announced it had received European approval to market Mycamine, a drug to prevent Candida infections in blood stem cell transplants, which include bone marrow transplants and to treat Candida fungal infections of the oesophagus. (Editing by Michael Watson)