Medication Protects Patients with Peanut Allergies
Study Shows Life-Threatening Reactions from Accidental Ingestion Can Be Avoided
A new medication could help most people with peanut allergies avoid life-threatening allergic reactions, according to a report in the March 14 issue of the New England Journal of Medicine. A research team led by Donald Leung, MD, PhD of National Jewish Medical and Research Center, and Hugh Sampson, MD of Mount Sinai School of Medicine, found that treatment with an anti-IgE antibody raised the average level at which study participants began reacting to peanuts from about half a peanut to almost nine peanuts.
Researchers estimate that most of the 50-100 annual fatal reactions to peanuts occur after an allergic person accidentally eats the equivalent of just one to two nuts. The researchers also presented their findings March 10 in Denver at the annual meeting of the American Academy of Allergy, Asthma & Immunology.
IgE is the molecule that binds to a group of cells called mast cells, which then trigger the allergic response. Food allergy symptoms can range from nausea and itching to anaphylactic shock and death. TNX-901, the treatment used in this study, is a genetically engineered antibody made by Tanox Inc. that binds to the IgE molecule and prevents it from triggering the allergic response.
"Our results indicate that the anti-IgE antibody could become the first preventive medicine for peanut allergies," said Dr. Leung. "If future studies bear out this initial promise, anti-IgE could not only save lives, but help lift a cloud of fear that people with peanut allergies live under every time they eat."
Approximately 1.5 million people in the U.S. have peanut allergy, the leading cause of severe allergic reactions. Each year, thousands of people rush to hospital emergency rooms, and approximately 50 to 100 people die after accidentally eating peanuts. Strict avoidance is the only means of preventing an allergic reaction. But, that can be difficult to impossible, especially, since food labels do not always mention tiny amounts of peanuts that are found in some foods.
An earlier study found that fatal reactions can occur after such difficult-to-avoid situations as eating a tuna sandwich made with a knife that had not been thoroughly cleaned after spreading peanut butter or eating cookies that were made on factory equipment that had earlier been used to make other cookies with peanuts. Existing medications, including epinephrine, antihistamines, bronchodilators, and charcoal pills, are taken only after the peanuts have been eaten and are not always effective.
"Anti-IgE therapy is not a cure for peanut allergy," said Dr. Sampson. "We believe that patients would have to continue the injections for the benefits to persist and they still would need to be careful about what they eat. But, because the amount they could consume without serious reaction would be greatly increased, the fear of accidental ingestion that detracts from quality of life for many patients would be eliminated. These are very promising results."
Blocking IgE is considered a major advance because it inhibits the allergic response at an earlier stage than other medicines, effectively stopping it before it begins. A slightly different anti-IgE molecule has shown promise in treating severe hay fever and asthma.
In the current randomized, double-blinded, placebo-controlled study, 82 people ages 12 to 60 with severe peanut allergy were given four injections at monthly intervals of either a placebo or one of three doses (150 mg, 300 mg, or 450mg) of TNX-901. Before the trial began, each patient underwent an oral food challenge with increasing doses of peanut flour and a food challenge with a placebo to establish their sensitivity to peanuts.
Patients were monitored closely during the challenges. Each challenge was halted and treatment begun as soon as a doctor determined that an allergic reaction had begun. Symptoms that commonly signaled an allergic reaction included nausea, abdominal pain, vomiting, throat or chest tightness, wheezing, itching, cough, and hives. Each patient's threshold sensitivity to peanuts was considered the amount of peanut flour consumed immediately before the challenge was stopped. TNX-901 was well tolerated with no significant side effects.
Blood levels of IgE were measured before the injections began and periodically throughout the test. Two to four weeks after the final injection, patients underwent one more food challenge with peanut flour.
TNX-901 raised patients' threshold sensitivity to peanut flour in a dose-responsive manner. The threshold sensitivity for patients receiving the largest dose (450 mg) of TNX-901 increased from an average of 177 mg to 2,805 mg. The average accidental ingestion is estimated to one to two peanuts or about 325 mg to 650 mg. Nearly a quarter of the patients receiving the highest dose of TNX-901 consumed 8,000 mg, or about 24 peanuts, with no reaction. Many patients still reacted to peanuts even after the injections. But on average, they could eat more peanuts without a reaction, and reacted less vigorously to the peanuts they did eat.
Other medical centers participating in the trial included Mayo Clinic in Rochester, MN; Arkansas Children's Hospital in Little Rock, AR; and Children's Hospital in Boston, MA.
