Pemetrexed Disodium Salt Heptahydrate is primarily used in chemotherapy for the treatment of certain types of cancer. It is most commonly administered for non-small cell lung cancer (NSCLC), particularly in cases where the cancer is locally advanced or metastatic. It is also effective in treating malignant pleural mesothelioma, often in combination with cisplatin. The drug works by inhibiting several enzymes involved in the synthesis of nucleotides, thereby preventing the growth and replication of cancer cells. It is typically given intravenously and requires premedication with folic acid and vitamin B12 to reduce potential side effects. Regular monitoring of blood counts and kidney function is essential during treatment to manage any adverse effects.