Allergen immunotherapy to desensitize patients from allergic rhinitis and asthma has been practiced for many many years. It is usually administered via subcutaneous injections (allergy shots, SCIT). Although very effective, it requires regular injections in allergist’s office for a period of 3-5 years. Patients receiving shots are under the potential risk of having serious systemic allergic reactions.
An alternate approach of desensitization is to administer allergen underneath the tongue (sublingual immunotherapy, SLIT). The allergen is given as either a dissolvable tablet or as a liquid extract. Compared with the injection immunotherapy, SLIT can be self- administered by patients or caregivers at home, does not require injections, and carries a much lower risk of severe allergic reactions.
SLIT has been used in Europe and Canada for years. In April 2014, the US Food and Drug Administration (FDA) approved Oralair (a mixed five-grass tablet by Stallergenes), Grastek (a timothy grass tablet by Merck), and Ragwitek (a short ragweed tablet by Merck). These SLIT are used in patients with significant allergic rhinitis during grass (Oralair and Grastek) or ragweed (Ragwitek) seasons but are not on allergy shots or other SLIT. While allergy shots are usually given in patients 5 yo and above, Oralair is approved in patients aged 10 to 65 yo, Grastek is approved for 5 to 65 yo, and Ragwitek is approved in adults 18 to 65 yo. SLIT may not be suitable for patients with certain medical conditions that may reduce their ability to survive a serious allergic reaction, or those taking beta-blockers which may render them unresponsive to epinephrine. It is contraindicated in patients with severe, unstable or uncontrolled asthma; with a history of severe allergic reactions to SLIT or its inactive ingredients; or with a history of eosinophilic esophagitis.
The treatment should be started 3 months (Grastek or Ragwitek) or 4 months (Oralair) prior to the expected onset of the grass or ragweed season and continued throughout the season. The most common adverse effects are mouth itchiness, throat irritation, ear pruritus, oral edema. The first dose should be taken in the allergist’s office under supervision, and the patient should be observed for at least 30 minutes for signs of allergic reactions. If the patient tolerates the first dose, the subsequent doses can be administered once a day at home. The physician will instruct the patient how to recognize and treat allergic reactions, and prescribe and train the patient how to use an epinephrine auto-injector if a severe allergic reaction (anaphylaxis) happens.