Chemotherapy drug. Computer model of a molecule of the intravenous chemotherapy drug gemcitabine. Atoms are represented as spheres and are colour- coded: carbon (yellow), hydrogen (white), oxygen (red), nitrogen (blue) and fluorine (green). Gemcitabine (brand name Gemzar) is used to treat non-small cell lung cancer, pancreatic, bladder and breast cancers. It belongs to a family of drugs known as antimetabolites. These drugs closely resemble a substance, or metabolite, that is essential for a cell's normal biochemical reactions. By replacing the metabolite, the drug prevents the cells from growing or reproducing.