• Injections of diluted extracts of the allergen are given on a regular schedule, usually twice a week to weekly at first, then in increasing doses until a maintenance dose has been reached. It usually takes several months and may take up to 3 years to reach a maintenance dose.
• At that time, intervals between shots can be 2 - 4 weeks, and the treatment is continued for another 3 - 5 years.
• Patients can experience some relief within 3 - 6 months. If there is no benefit within 12 - 18 months, discontinue the shots.

After stopping immunotherapy, about a third of allergy sufferers no longer have any symptoms, a third have improved symptoms, and a third relapse.

The use of an injection series is effective, but patients often fail to comply with the regimens. Some other schedules and delivery methods are being investigated that might make the program easier and less distressing.

Rush Immunotherapy. Investigators are studying "rush immunotherapy," in which patients achieve the full maintenance dose with several shots a day over a period of 3 - 5 days. Rush therapy uses modifications that reduce the risk of severe reactions to excessive doses. Studies suggest that it is effective and safe, but anaphylaxis and severe reactions can occur. Patients must be selected carefully and must be monitored closely during this period for severe reactions.

Oral Forms. Trials are underway to test forms of immunotherapy taken by mouth as an alternative to allergy shots. These methods include using a pill taken by mouth or a sublingual (under-the-tongue) tablet. Although oral and sublingual immunotherapy is prescribed in many countries in Europe and South America, it is not approved in the United States and is not considered accepted therapy at this time.

Side Effects and Complications of Immunotherapy

Injections for ragweed and, sometimes, dust mites have higher risks for side effects than other allergy shots. If complications or allergic reactions develop, they usually occur within 20 minutes, although some can develop up to 2 hours after the shot is given.

Side effects of immunotherapy include:

• General itching, swelling, red eyes, hives, soreness at the injection site.
• Less common side effects are low blood pressure, asthma worsening, or difficulty breathing. This is due to an extreme hypersensitivity response called anaphylaxis. It can also occur if excessive doses are given.
• In rare cases, particularly because of excessive doses or if a patient has a serious lung problem, severe reactions can occur, which can be life threatening.
• Premedicating patients with antihistamines and corticosteroids may help reduce the risk of reactions to immunotherapy, although this could mask early warning signs.

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Review Date: 05/03/2011
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)