SAN ANTONIO – Omalizumab diminished the signs and symptoms of chronic idiopathic urticaria in a dose-dependent fashion in a phase III study of 323 patients who failed to respond adequately to H1-antihistamines.
After 12 weeks of treatment with the recombinant humanized monoclonal antibody, improvements from baseline in weekly itch-severity scores were significantly greater in patients randomized to receive three doses of either 300 mg or 150 mg every 4 weeks, compared with placebo (score change of -9.8 and -8.1 vs. -5.1, respectively). The itch-severity score in patients randomized to receive a 75-mg dose changed by -5.9 points, but this did not differ significantly from the change in the placebo group, according to Dr. Marcus Maurer of Charite-Universitatsmedizin, Berlin. The report was published online on Feb. 24 in the New England Journal of Medicine.
The findings from this international double-blind trial were reported simultaneously at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
In addition to meeting the primary 12-week response endpoint of change in weekly itch-severity score, patients receiving the 300-mg and 150-mg doses of omalizumab also experienced significant improvements, compared with patients given placebo, on all but one secondary endpoint, including change in the 7-day urticaria activity score (UAS7), change in the score for the weekly number of hives, time until a reduction from baseline of at least 5 points in the weekly itch-severity score (the MID), the proportions of patients with a UAS7 of 6 or less, the number of patients with a weekly MID response in the itch-severity score, the change from baseline in the score for the size of the largest hive, and change from baseline in the overall score on the Dermatology Life Quality Index. Those receiving 300 mg, but not those receiving 150 mg, also experienced significant improvement in the proportion of angioedema-free days from weeks 4-12 (N. Engl. J. Med. 2013 Feb. 24 [doi:10.1056/NEJMoa1215372]).
In a post hoc analysis at 12 weeks, 53%, 23%, 18%, and 10%, of those in the 300-mg, 150-mg, 75-mg, and placebo groups, respectively, were completely free of hives, and 44%, 22%, 16%, and 5%, respectively, were free of both hives and itching.
Of note, many patients experienced extremely rapid improvement, raising questions about a potential, as-yet unidentified and fundamental characteristic of this disease, study coauthors Dr. Thomas B. Casale, professor of medicine and medical microbiology and immunology and chief of allergy/immunology at Creighton University Medical Center, Omaha, Neb., and Dr. Allen P. Kaplan, clinical professor of medicine at the Medical University of South Carolina, Charleston, reported during a press briefing at AAAAI.
They explained that omalizumab, currently approved as an add-on therapy for moderate to severe persistent allergic asthma, is known to bind the allergic antibody immunoglobulin E (IgE). Many patients with chronic urticaria have an antibody that binds to a protein on the surface of histamine-containing cells, and that protein binds IgE.
"Just one injection drops one’s IgE level pretty close to zero ... and we learned that when we drop IgE to rock bottom, the protein on the cell to which it is attached also drops – and that’s the protein that the circulating antibody interacts with. The thinking was that if we drop the surface protein low enough, there’s nothing for the antibody to react with, and the hives would improve," he said.
This was, in fact, the case, as demonstrated in a phase I study of 12 patients, in which 7 patients responded dramatically, 4 responded partially, and 1 had no response. These findings led to the current phase III study, which is one of three such studies that investigators hope will lead to the drug’s approval for chronic idiopathic urticaria, because the high cost of the drug is prohibitive with respect to off-label use.
The same effect was seen in the current study.
This effect, however, takes a couple weeks to become apparent, so the rapid responses that occur in numerous patients suggest there is something more at play.
"This is working even faster than we thought, and probably there is a function of the allergic antibody that we do not yet understand," Dr. Kaplan said. "So this is going to be not only a terrific therapy for the disorder, but will lead to research in the future that probably – we hope – will elucidate the underlying abnormality of chronic urticaria beyond our current understanding of it. It’s very exciting, because it might elucidate some fundamental analogy that we don’t appreciate, and would have implications for allergic disease across the board."