The FDA has announced new “black box” labeling for Genentech’s Xolair (omalizumab) to address the risk of anaphylaxis in patients using the asthma drug.

The new labeling, the FDA’s strictest, indicates that patient reports following the drug’s approval in 2003 through 2006 noted cases of anaphylaxis were seen in roughly two out of 1000 patients.

Genentech collaborates with Novartis on the marketing of Xolair, which had $425 million in global sales last year.