Sodium metabisulfite

Sodium metabisulfite is a chemical compound (Na2S2O5). It is used commercially as a disinfectant, antioxidant and preservative.
In medicine, it is commonly added to the Epipen and local anesthetics like lidocaine to extend their shelf life. However, as it has the same chemical arrangement as sulfa drugs, it will cause an allergic reaction in persons sensitive to sulfites. 
It is used in many laboratory tests due to its effect on abnormal hemoglobin and can confirm diseases like sickle cell anemia.
Sodium metabisulfite at Wikipedia
Category:Chemistry