The FDA and biotech company Genentech have revised the safety warnings for the psoriasis drug Raptiva.

The revisions include a new warning about a type of anemia called immune-mediated hemolytic anemia. This type of anemia occurs when the immune system mistakes oxygen-carrying red blood cells for foreign substances and destroys them.

The warning also concerns reports of serious infections and a rare blood disease called thrombocytopenia, characterized by low levels of blood-clotting cells called platelets.

The changes are described in a letter to health care providers from Hal Barron, MD, Genentech's senior vice president for development and chief medical officer.

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About Raptiva

Raptiva is approved for adults aged 18 and older with longstanding moderate-to-severe psoriasis.

It's a so-called biologic agent to treat the problems at the heart of psoriasis. Raptiva is a designer antibody; it's designed to throw a monkey wrench into the mechanisms by which immune cells cause psoriasis.

The FDA approved Raptiva in October 2003.

Read WebMD's "Learn More About Raptiva"

New Anemia Warning

Two cases of hemolytic anemia were observed in Raptiva's clinical trials, and two others were reported after the drug went on the market, Barron's letter states.

In two cases, the patient's hemoglobin -- the protein that carries oxygen -- dropped to severely low levels.

Raptiva has not been shown to have caused those events, but that possibility can't be ruled out, the letter states.

The cases of hemolytic anemia were diagnosed four to six months after starting Raptiva.

Raptiva should be discontinued if hemolytic anemia occurs.

Symptoms of hemolytic anemia include: easy fatigue and loss of energy, rapid heartbeat, especially with exercise, shortness of breath, jaundice (yellow skin), brown or red urine, abdominal pain.

Read WebMD's "Newly Diagnosed with Psoriasis? Start Here"

Updated Infection, Blood Disease Warnings

Raptiva's warnings section concerning serious infections has also been updated. The update includes rare reports of the following infections:

Necrotizing fasciitis-- rapidly spreading infection that leads to death of tissues located underneath the skin Pneumonia due to tuberculosis Severe bloodstream infection Severe pneumonia with low levels of infection-fighting white blood cells Worsening of infection (skin infections, pneumonia) despite antibiotic treatment

The warnings section also includes reports of thrombocytopenia.

"Genentech is committed to ensuring that Raptiva is used safely and effectively," Barron says in the letter.

Genentech is a WebMD sponsor.

By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: News release, FDA. Letter, Genentech. WebMD Medical News: "Raptiva Approved for Psoriasis Treatment."