Selling $7.9 billion worth of a drug annually has put a target on the back of Abbott Labs' (NYSE: ABT) Humira. Two companies presented data from head-to-head trials pitting their drugs against Humira at the European League Against Rheumatism annual meeting.

Bristol-Myers Squibb's (NYSE: BMY) Orencia proved just as effective as Humira at treating patients with rheumatoid arthritis. After one year of treatment, 64.8% of patients taking Orencia plus a generic called methotrexate saw their symptoms improve by 20% compared to 63.4% of patients taking Humira plus methotrexate.

Being just as good as the leader might seem like a win, but I'm not sure it'll be enough to capture a large chunk of Humira's market share. On a whole, Orencia appears to have a better safety profile; only 3.5% of patients taking Orencia dropped out of the study because of adverse events compared to 6.1% for Humira patients. But Orencia had more autoimmune events, which are likely drug-related since the drugs work by tempering the overactive immune system that causes the rheumatoid arthritis attacks.

More worrisome for Abbott is Roche's Actemra, which goes by RoActemra in Europe. The drug didn't just match Humira, it actually beat it. Using the same scale as the Orencia trial, Actemra improved symptoms in 65% of patients compared to just 49% of Humira-treated patients.

That's a solid win for Actemra, but don't expect prescription habits to change overnight. Doctors are comfortable with Humira, as witnessed by the nearly $8 billion in sales last year, which gives the drug a distinct advantage compared to Actemra, which just gained U.S. approval in 2010. In fact, Roche will have to get the new data added to the label before it can market Actemra as a direct competitor to Humira. The drug is currently approved as a treatment for patients who have failed a TNF inhibitor, a class that includes Humira, Pfizer (NYSE: PFE) and Amgen's (Nasdaq: AMGN) Enbrel, and Johnson & Johnson's (NYSE: JNJ) Remicade.

While the injected and infused drugs are all fighting for market share among themselves, Pfizer is hoping to move into the market with its oral rheumatoid arthritis treatment, tofacitinib. After a solid 8-2 vote from a Food and Drug Administration advisory committee, an approval in August looks likely. Like Actemra, tofacitinib might be initially approved as a post-TNF-inhibitor treatment, which will take one of the targets off Humira's back at least for a little while.

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