Allergy shots can cause systemic side effects: Study

Aug 9 2010

Allergy shots can reduce symptoms of asthma, use of inhaled medications and allergy-related asthma attacks, confirms an updated review of studies. Yet, the treatment can also cause systemic side effects that range from a stuffy nose to fatal anaphylactic shock.

About 30 percent of asthma patients experience improved breathing after receiving a series of injections that desensitize their immune systems to specific irritants, according to the review. The medical term for this treatment protocol is allergen immunotherapy.

The number of patients experiencing systemic reactions of any severity nears 20 percent, the reviewers say, although they note that more than 8 percent of patients receiving placebo experience similar reactions. Fatalities remain extremely rare at one death per 2.5 million injections.

Allergic asthma is the most common form of asthma, affecting over 50 percent of the 20 million asthma sufferers in the United States, according to the Asthma and Allergy Foundation of America. Asthma is responsible for more than 2 million visits to U.S. emergency rooms and 4,000 deaths each year.

"Whilst inhaled corticosteroid therapy remains the mainstay of asthma management, any reduction in this type of treatment while maintaining good asthma control would be welcome," the authors write.

The review provides evidence to help patients and their doctors have a "sensible discussion" about the benefits versus risks of immunotherapy, said co-author Michael Abramson, Ph.D., a pulmonologist at Monash University in Melbourne, Australia

Immunotherapy is most risky for patients with poorly controlled asthma, said Harold Nelson, M.D., of National Jewish Health, a Denver hospital specializing in respiratory, cardiac, immune and related disorders. Nelson is an international authority on immunotherapy. "People with treatment-resistant asthma are not candidates for allergy shots," he said.

Allergists should also review each patient's symptoms before every injection, Nelson said. "Patients shouldn't be actively wheezing, they shouldn't be waking up at night due to asthma symptoms and their pulmonary function should be relatively normal." If symptoms are flaring up, doctors should postpone the injection.

Professional guidelines recommend that patients remain under observation for 30 to 45 minutes after an injection, so that clinicians can recognize any serious reactions and treat them immediately.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.

The meta-analysis encompasses 88 studies, with 13 published since 2001, and about 3,800 participants. All studies were randomized controlled trials. Most of the studies focus on house mite or pollen allergies, while a few looked at animal dander, mold, latex or a combination of allergens.

"Among allergists there's no question that asthma caused by allergies is responsive to immunotherapy," Nelson said. "The advantage of immunotherapy is that it causes long-lasting, if not permanent, improvement."

Furthermore, most people who have allergy-induced asthma also have nasal symptoms, Nelson said. "They have to inhale steroids into their lungs and spray them into their nose, and a lot of people don't like to do that forever. Immunotherapy treats both the nasal and chest symptoms."

Abramson, for his part, now also encourages doctors to consider immunotherapy for appropriate patients. He describes the risk of side effects as "acceptable but definite" for both adults and children.

The review authors say that allergy drops, which patients place under the tongue, might offer effective asthma control with a reduced risk of serious side effects. While widely used in Europe and the United Kingdom, the U.S. Food and Drug Administration has not yet approved "sublingual immunotherapy."

"During my training as a respiratory physician, I was taught that this was a potentially dangerous form of therapy that was of no benefit in asthma, Abramson said. "I personally have changed my views since working on this series of reviews."

SOURCE The Cochrane Library