Be aggressive with suspected peanut allergy

Pediatric News, Nov, 2005 by Doug Brunk

YOSEMITE, CALIF. -- A 13-month-old girl eats one bite of a peanut butter sandwich and vomits immediately. Hives start to appear on her face and trunk, and her face starts to turn red. She also starts to cough and becomes irritable.

If your approach to treating this classic description of peanut allergy is to have the girl take an antihistamine and "see what happens," you are not practicing proper medical care, Laurie J. Smith, M.D., said at a pediatric conference sponsored by Symposia Medicus.

"When you have an acute, witnessed, IgE-mediated event--even if the early symptoms are mild, such as a few hives--you need to be very aggressive in your approach to this problem," said Dr. Smith, of the department of allergy and immunology at Walter Reed Army Medical Center, Washington. 'Appropriate therapy for an acute IgE-mediated reaction is epinephrine, which should be given IM, preferably in the lateral thigh."

She offered three reasons why antihistamines are not a first-line therapy for peanut allergy and other IgE-mediated reactions:

First, antihistamines are slowly absorbed. They don't peak until 4 hours after ingestion. Second, they may help relieve hives and itching, but they have no antianaphylactic properties. "The things that can kill you with an acute allergic event are either cardiovascular or respiratory [in nature]," she said. "Antihistamines do absolutely nothing for that." Third, epinephrine shuts off mast cell mediator release. "That means it's turning off the [allergic] reaction," she noted. "Antihistamines do not do that."

Antihistamines do play a role in treatment, but only after epinephrine is administered. Then, depending on the symptoms, the child should be treated with other agents, such as inhaled bronchodilators and oxygen for bronchospasm, and fluids and pressors for hypotension.

Most severe IgE-mediated reactions have a sudden onset of severe symptoms, but not always. For example, in biphasic anaphylaxis, a patient presents with initial symptoms that clear with or without treatment. "Then 2, 4, 6, or 8 hours later, they have a recurrence of the symptoms--sometimes even more severe--that can lead to fatality," said Dr. Smith.

Protracted anaphylaxis also can occur. In this condition, someone presents to your office with acute symptoms that persist over hours to days. "There are case reports of people who have required pressor treatment for 24-36 hours," she noted. "Persistent shock is a potential event, as is severe respiratory compromise--wheezing or angioedema occurring hours after the initial event. That's one of the reasons why these patients need to be observed for longer than just an hour [after onset of symptoms]."

Risk factors for a severe allergic reaction include previous severe reaction to a food, a personal history of asthma, a personal history of severe atopy, and known allergy to peanuts or tree nuts.

A convincing history may be all you need to diagnose a case of peanut allergy. You can perform a skin test or a radioallergosorbent test (RAST) on the child. But Dr. Smith noted that allergy skin testing for foods is an imprecise science. "We estimate that 50%-60% of the positive tests mean sensitization but do not correlate with actual symptoms if the person ingests that food," she said. "It's not uncommon to get several positive skin tests to foods in these children, and you have to interpret. Sometimes we see children who have been sent to an allergist because they may have had milk allergy at 6 months of age. The allergist skin-tested them or did a RAST test for things they'd never even eaten, such as peanuts, and they tested positive. So they've never eaten peanuts; they've never had a reaction; but they have this positive test. If you follow those kids, about one-third of them will go on to react to peanuts upon subsequent ingestion, even though all of them have evidence of sensitization on a blood test."

Dr. Smith routinely prescribes six EpiPen Jr. devices for children with known peanut allergy: two for school, two for after-school day care, and two for home. It's important to "have the EpiPens within 5 minutes of the child all of the time," she said. "It's not at home, or in the glove compartment. It's not in the mother's purse when the child is at the babysitter."

She developed a sliding scale for using the EpiPen Jr., depending on whether the child has asthma, what the culprit food is, and how severe the reactions have been. "If the food is peanut or nuts, I say use your EpiPen immediately, even if you only think you've gotten the food into your mouth," she advised. "Don't wait for symptoms."

If the child has asthma, inject the EpiPen at the first sign of an IgE-mediated symptom. "It needs to be taken seriously, as if it is a potential emergency," she said. "The message in the medical literature has been that a severe reaction may not be predicted by how soon the symptoms start or how severe the symptoms are."

If a child presents with no risk factors for a severe allergic reaction, if they've had mild reactions before, if they don't have asthma, and if the antigen is not peanuts, "I might say, wait and watch with your EpiPen available," Dr. Smith said. "At the first sign of any other symptom--they vomit, they cough, and their nose starts to run--give the epinephrine. After you give it, proceed to the [emergency department] or call 911."