The disodium salt of a synthetic pyrimidine-based antifolate. Pemetrexed binds to and inhibits the enzyme thymidylate synthase (TS) which catalyses the methylation of 2'-deoxyuridine-5'-monophosphate (dUMP) to 2'-deoxythymidine-5'-monophosphate (dTMP), an essential precursor in DNA synthesis. or A drug used alone or with another drug to treat certain types of non-small cell lung cancer and malignant pleural mesothelioma. It is being studied in the treatment of other types of cancer. Pemetrexed disodium blocks DNA synthesis and may kill cancer cells. It is a type of folate antagonist. Also called Alimta and LY231514.