A drug used alone or with cisplatin to treat certain types of non-small cell lung cancer that is locally advanced or has spread to other parts of the body. It is also used with cisplatin to treat malignant pleural mesothelioma in patients whose cancer cannot be treated with surgery. It is also being studied in the treatment of other types of cancer. Pemetrexed disodium stops cells from using folic acid to make DNA and may kill cancer cells. It is a type of folate antagonist. Also called Alimta and LY231514.