Help for patients with drug allergy

Desensitization can allow many to tolerate meds

By Lauran Neergaard
Associated Press / April 13, 2010

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WASHINGTON — Having a bad reaction to penicillin as a child does not guarantee you are still allergic decades later. And if the oncologist says you have to switch chemotherapies because of an allergic reaction, well, maybe not.

More medical centers are recommending a lesser-known choice: drug desensitization, a carefully controlled method of helping patients temporarily tolerate medications — from aspirin to antibiotics to chemo — that their bodies once rejected.

Not everyone is a candidate. But for those who are, the process can mean the difference between getting the best treatment or a runner-up that may not do the job, says Dr. Mariana Castells, an allergist at Harvard Medical School and Brigham and Women’s Hospital in Boston who helped pioneer the care.

“You don’t know how lucky I feel’’ to have been desensitized, says Vanessa Greenleaf of Marblehead, Mass.

Greenleaf developed a severe allergy to carboplatin, a mainstay of her treatment for ovarian cancer.

Even as a burning sensation engulfed her body during the allergic attack, Greenleaf’s chief fear was that doctors at Massachusetts General Hospital would take her off the chemo combination she believed her best shot.

“I kept mumbling, ‘I want to stay on,’ ’’ recalls Greenleaf, 52, who eventually got her wish. “All the nurses kept telling me, ‘You can, we’ll get the drug into you safely.’ ’’

Allergies make up 5 to 10 percent of all adverse reactions to medications, according to the American Academy of Allergy, Asthma, and Immunology. Sometimes drug allergies kill. So anyone who has ever reported an allergic reaction to a medicine, even decades earlier, is told never to take that drug.

Penicillin and related antibiotics are a leading trigger, as are anti-inflammatory painkillers like aspirin. But increasingly, severe reactions to some leading cancer therapies are being reported, including allergies developed by more than a quarter of patients who take widely used platinum-based chemos.

In one common approach to neutralizing hay fever reactions, patients get small doses of the problem allergen for a few years until they build up a tolerance to it. More recently, allergists have begun testing similar therapy for children with life-threatening food allergies.

Desensitization for drug allergies is the same concept. It was first started for penicillin allergies and expanded to chemo in recent years: Tiny, diluted amounts of the problem drug, sometimes with anti-allergy medicines, are given in slowly escalating doses over hours to a day — usually in the hospital or even the intensive care unit for safety — until reaching the optimal dose.

But desensitization’s effects last only as long as the patient is taking a daily dose of that medication. That means chemo patients, for instance, must get desensitized all over again before each new treatment cycle.

First step: Prove the allergy. About 30 percent of penicillin allergies can disappear in a decade or so as immune cells age and are replaced, but only testing can tell, says Dr. Elina Jerschow, who directs a newly opened drug desensitization program at Montefiore Medical Center in New York.

A skin test for penicillin allergy returned to the market last fall after an absence of several years.

Castells’s office is working through a waiting list of people eager to be tested. Many other drugs lack a skin test and may require a challenge, in which a small amount of the drug is administered to the patient in the doctor’s office or hospital to be sure of the diagnosis.

When patients do not have a good alternative, customized desensitization can calm the immune cells that control this allergic response.