Roche and partner Biogen Idec (NASDAQ:BIIB) are off to a good start with their rheumatoid arthritis drug candidate, ocrelizumab, but there's still a ways to go before we can put revenue from the potential blockbuster onto the income statement.

Phase 3 trial results released today were brief, but said that ocrelizumab combined with methotrexate -- a standard early treatment for rheumatoid arthritis -- worked better than methotrexate alone in patients who weren't getting an adequate response from methotrexate.

Roche reported "a higher percentage of serious infections" for patients taking ocrelizumab, but without the full details, it's hard to determine whether that could derail the drug or not. Warnings about serious infections on their labels haven't stopped Pfizer (NYSE:PFE) and Amgen's (NASDAQ:AMGN) Enbrel, Abbott Labs' (NYSE:ABT) Humira, and Johnson & Johnson (NYSE:JNJ) and Merck's (NYSE:MRK) Remicade from becoming blockbusters many times over.

The drug is in three other phase 3 trials that should report results in the first half of next year. Unfortunately 25% of the trials being positive doesn't equate into 25% of sales, or even 25% approval. Biogen and Roche will still need the other trials to come through before they'll be able to get the regulators to sign off on the drug.

Ocrelizumab is a follow up to the duo's rheumatoid arthritis and cancer drug, Rituxan. For rheumatoid arthritis patients, Rituxan is only approved for patients who have failed an anti-TNF alpha treatment: Enbrel, Humira, and Remicade. If Biogen and Roche can get ocrelizumab approved for treating patients earlier in the treatment cycle with manageable side effects, it should be a nice addition to their portfolios.

We'll need a little more data to know whether that's possible.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.