Genentech's Unique Drug

Genentech (NYSE: DNA  ) and Biogen Idec's (Nasdaq: BIIB  ) Phase II trial demonstrating Rituxan's effectiveness in treating moderate-to-severe rheumatoid arthritis was enshrined in the prestigious pages of the New England Journal of Medicine, adding heft to the study's results.

The findings, first released in 2002, showed that Rituxan, administered either alone or in combination with another drug, improved patients' symptoms for as long as 48 weeks. The publication should raise the profile of the drug -- first approved for the treatment of certain forms of non-Hodgkin's lymphoma back in 1997 -- among physicians who treat arthritis.

Phase III trials of Rituxan for arthritis are already under way, and given its widespread and long-term use for cancer, its chances for approval seem extremely good. If it is approved for the arthritis, though, Rituxan will hardly have a monopoly on the marketplace. The medicine would join other newer treatments that include Abbott Laboratories' (NYSE: ABT  ) Humira, Johnson & Johnson (NYSE: JNJ  ) and Schering-Plough's (NYSE: SGP  ) Remicade, and Amgen (Nasdaq: AMGN  ) and Wyeth's (NYSE: WYE  ) Enbrel. What makes all of these drugs even more tantalizing is that they could be effective against other autoimmune diseases. Rituxan's competitors, for instance, are all being tested to treat psoriasis.

Notably, though, Humira, Remicade, and Enbrel all concentrate on the same protein, TNF-alpha, to achieve results. Rituxan, meanwhile, stands apart by targeting B-cells (a type of white blood cells). This different mechanism of action could pay off over the long haul. While the competing drugs operate differently enough so that one may succeed where another fails, Rituxan's uniqueness could make it the second-line therapy of choice when a TNF-alpha drug is not effective.

Genentech and Biogen Idec are both richly valued. But given their experience with drugs using this distinct mechanism of action, and the promise such treatments hold, the long-term potential for both companies seems great.

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Fool contributor Brian Gorman is a freelance writer living in Chicago, Ill. He does not own shares of any companies mentioned here.