Biogen Idec ( BIIB) and partner Elan ( ELN) said Monday afternoon that the Food and Drug Administration cleared Tysabri for treatment of Crohn's disease (CD).

The drug, already used for relapsing multiple sclerosis, is now approved for patients with moderately to severely active CD, a chronic and progressive inflammatory disease of the gastrointestinal tract. It's specifically indicated for CD patients who've tried conventional treatment to no avail.

The FDA was originally scheduled to make a decision on the drug by mid-October, but pushed back the review three extra months in order to review a risk-management plan.

Cambridge, Mass-based Biogen said the approval is accompanied by "robust labeling" with safety warnings and a CD-specific risk management plan to minimize potential risk of progressive multifocal leukoencephalopathy (PML) and other serious infections. In 2005, a possible link to PML pushed the drug off the market as a treatment for multiple sclerosis, but there have been no recent occurrences of the deadly viral infection of the brain with regard to Tysabri.

Biogen shares closed up 96 cents, or 1.6%, at $59.98, and were up another 41 cents at $60.39 in recent after-hours trading. Elan, which ended the regular session up 13 cents, or 0.5% at $24.89, were recently trading down 4 cents at $24.85 post-close. The companies have a 50/50 interest in the drug.

About 500,000 people in the U.S. have CD, according to Biogen, which expects to distribute the product for CD by the end of February.

The drug will compete with Johnson & Johnson's ( JNJ) Remicade, the leading treatment for the disease. Other Crohn's disease treatments include Abbott's ( ABT) Humira, which was launched in the U.S. and Europe in the first half of 2007.