The first drug made using genetically engineered animals is now on sale in the United States.

The drug, called ATryn, is an intravenous anti-clotting therapy made using a human protein gathered from female goats specially bred to produce it in their milk.

The medicine aims to prevent excessive blood clots in patients with a disorder known as hereditary antithrombin deficiency, which affects approximately one in 2,000 to one in 5,000 people. It was approved by the Food and Drug Administration in February.

The goats are bred using cells injected with human DNA in a process the drugmaker says is a cost effective way to produce human antithrombin, a natural anti-clotting protein.

The drug is being marketed by the U.S. arm of the pharmaceutical company Lundbeck, the Danish drugmaker said on Wednesday.

The company has a herd of about 200 goats in Massachusetts.