Just a month after Abbott Laboratories (NYSE: ABT) snagged a fifth approval for its anti-inflammatory Humira, the FDA approved the biotech drug to treat another disease.

The most recent approval is for the treatment of juvenile idiopathic arthritis, commonly referred to as juvenile rheumatoid arthritis. Humira is already approved to treat the adult version of the disease, which leaves patients with painfully stiff, swollen joints.

Having never met a kid who likes getting shots, I'm going to go out on a limb and say that Humira will compete well with Amgen (Nasdaq: AMGN) and Wyeth's (NYSE: WYE) Enbrel, since Humira has a more convenient every-other-week dosing compared to Enbrel's twice weekly. On the other hand, it's unlikely that Humira will be a first-line choice of doctors, since they consider nonsteroidal anti-inflammatory drugs (NSAID) like Pfizer's (NYSE: PFE) Celebrex safer, and kids definitely prefer popping pills to being stuck with needles.

No matter how much of a market Humira manages to capture, sales for this newest indication will be a small portion of the more than $3 billion in Humira sales that Abbott brought in last year. There are only about 50,000 children in the U.S. with the disease, compared to about 1.3 million adults with the condition (not to mention the other four diseases Humira treats). Nevertheless, the move into juvenile arthritis was probably a good one financially, since Abbott had to run only a small 171-subject trial to get approved for the additional indication.

Ultimately, the growth story for Humira -- and what will allow Abbott to reach its goal of 13%-14% EPS growth (excluding one-time items) -- is its launch into treating plaque psoriasis. Investors will get an early indication at how both launches are going at the end of this quarter, but they'll probably have to wait until the end of the second or third quarter before the additional growth really kicks in.

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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.