Pemetrexed disodium is primarily used in the treatment of certain types of cancer, particularly non-small cell lung cancer and malignant pleural mesothelioma. It is often administered in combination with other chemotherapy drugs, such as cisplatin, to enhance its effectiveness. The drug works by inhibiting several enzymes involved in the synthesis of nucleotides, thereby preventing cancer cells from growing and dividing.

In clinical settings, it is typically given as an intravenous infusion, with treatment cycles repeated every three weeks. Patients receiving this medication are often prescribed supplements like folic acid and vitamin B12 to reduce the risk of side effects, which can include fatigue, nausea, and low blood cell counts. Its targeted mechanism makes it a valuable option for patients with specific cancer types, especially when other treatments have proven ineffective.