Eribulin is an anti-cancer drug. Eribulin is a synthetic derivative of the Japanese sponge, Halichondria Okadai. This drug comes in the form of an injection. It is an anticancer drug that belongs to the group of drugs known as microtubule dynamics inhibitors. Eribulin works by stopping the growth and spread of cancerous cells. It is a prescription only drug that comes only with a prescription from the doctor.