GRASTEK® Allergen Extract and Warfarin

Publication Date: 
Sat, 08/01/2015
By: Alere Staff

During the spring and summer months many people are affected by seasonal allergies produced by plants and flowers that are in their prime growing season. Timothy grass, scientifically called Phelum Pretense, grows nationwide, typically as a weed in locations such as vacant lots, along fences and highways. It produces a long, narrow seed head that flowers and generates large amounts of pollen for approximately two weeks. 

Each Timothy grass flower head blooms at a different time so the allergic season can be long and bothersome for those allergic to grasses. As with many plants, if you are allergic to one type of grass the likelihood that allergic reactions occur with others is high. 

GRASTEK® medication is a new allergen extract available to help manage the allergic reaction and symptoms to Timothy grass and other grasses that is used sublingually or under the tongue. This medication can help with the sneezing, runny, congested or itchy nose and itchy and watery eyes. Although this medication does not give immediate relief, it allows tolerance to the allergen to be built over time by those that use it regularly. The GRASTEK® medication can be used on people age 5 to 65 with allergies to grass pollen.

According to the manufacturer, the dosing is typically one tablet placed under the tongue daily. The first dose is given in the doctor’s office so the patient can be watched for severe allergic reaction. If this is tolerated the dosing is then done at home, but the patient should have been given a prescribed EPI-Pen and instructed in its use. This dosing should begin about 12 weeks prior to prime grass allergy season and continue throughout the season. It can also be taken daily for three years to provide continue relief during the fourth year in which you do not take it daily.

A GRASTEK® Prescription and Warfarin

There does not appear to be any problems associated with using the GRASTEK® allergen extract in those who also take warfarin. Those who should not take the medication are people with severe, or unstable, or uncontrolled asthma, or those who have had severe allergic reactions in the past that include difficulty breathing, dizziness or fainting or rapid or weak heartbeat.  Although the GRASTEK® medication can cause severe allergic reactions the most common side effects reported with use were itching of mouth, lips or tongue, swelling under the tongue or throat irritation. 

As with any added medications, especially for those who take warfarin and are being treated for other medical conditions, it is recommended that you speak with your doctors to determine if this is an appropriate medication for addition to your care prior to using it.

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  1. Antigen Laboratories, Inc. Timothy Grass(Phleum pretense). University of Missouri. Retrieved July 21, 2015 from website:
  2. Merck Sharp & Dohme Corp. Highlights of Prescribing Information: GRASTEK (Timothy Grass Pollen Allergen Extract) [Package Insert]. 2014. Whitehouse Station, NJ. Merck & Co., Inc. Retrieved from website:

GRASTEK® is a registered trademark of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc. Alere is not affiliated or associated with Merck Sharp & Dohme Corp., Merck & Co., Inc. or the GRASTEK® trademark.