Definition: Antivenin is a drug used to treat bacterial infections. It's derived from a venom that comes from the snake Encephalopis melanogaster. Definition: Antivenin refers to a type of medication used to treat bacterial infections, which typically contains a combination of antivirals and antibiotics. Anten means first, and venin is an English term meaning "ant." So, antenvenin literally translates as the venom from the snake Encephalopis melanogaster.