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SLIT works the same way as allergy shots, but is administered by placing a pre-determined amount of antigens under the tongue. Benefits include convenience (SLIT is administered at home once a day) and appears to be safer than injections with less risk of systemic reaction - there have been no known life-threatening anaphylaxis reactions with SLIT in over 30 years, and over 200 million doses in Europe. The World Health Organization (WHO) has endorsed sublingual immunotherapy as a viable alternative to injection therapy.

Sublingual immunotherapy with allergy drops can be given for both environmental allergies (i.e. hay fever, seasonal or perennial allergies) as well as for certain food allergies. The usual treatment regimen consists of three drops of each vial under the tongue daily. Approximately every three months, the dose is adjusted and the new vial(s) are picked up at the allergist's office. Like allergy shots, the complete immunotherapy treatment course averages about 3-5 years.

Currently, the option of sublingual immunotherapy has not been approved for coverage by health insurance. The cost of treatment averages about $25.00 for 1 vial and $50.00 for 2 vials per month.

Side Effects of Immunotherapy

While the most common side effect of allergy vaccines is redness and itching at the injection site, there is a risk of systemic reactions during immunotherapy, especially during the induction or "up-dosing" phase. Approximately 5-10% of people receiving immunotherapy have systemic reactions, which are moderate to severe in 1-3% of cases. This is why the 30 minute observation period following injection is required. Reactions include urticaria (hives), respiratory symptoms, and low blood pressure. There have also been rare instances of death from severe anaphylactic reactions. Anaphylaxis is a severe, systemic allergic reaction caused by the systemic release of histamine and other mediators. Symptoms include swelling of the throat (laryngeal edema), lower-airway obstruction and hypotension. Treatment of anaphylaxis involves prompt administration of epinephrine which should reverse the actions of histamine within minutes. This treatment can be followed by a histamine blocker and corticosteroids.

Patients should not be taking beta-adrenergic blocking drugs or angiotensin-converting enzyme (ACE) inhibitor medications when receiving immunotherapy because these drugs may mask early signs and symptoms of a severe reaction (anaphylaxis). Other people for whom immunotherapy is not suggested include those with chronic lung disease, unstable angina or history of myocardial infarction (heart attack), uncontrolled hypertension, and major organ failure.

Because a systemic reaction occurring during pregnancy may produce severe fetal hypoxia or precipitate premature uterine contractions, immunotherapy should not be initiated during pregnancy. However, immunotherapy can be maintained during pregnancy provided the woman is tolerating and benefiting from the injections. The immunotherapy dose should not be increased during pregnancy.