This medication is used to help prevent swelling problems that occur with a certain immune disease passed down through families (hereditary angioedema-HAE). HAE is caused by low levels or improper function of a natural substance produced by the body (C1-inhibitor). Symptoms such as rapid swelling of the hands, feet, limbs, face, tongue, or throat can occur. Swelling of the intestinal tract may cause symptoms such as abdominal cramps, diarrhea, or vomiting. Attacks of swelling may occur without reason. However, anxiety, stress, sickness, and surgery may trigger attacks in some people. This medication increases the level of C1-inhibitor to help prevent attacks of sudden swelling due to hereditary angioedema.