Pemetrexed disodium is primarily used as a chemotherapy agent in the treatment of certain types of cancer. It is especially effective in non-small cell lung cancer (NSCLC), particularly the non-squamous subtype, where it is used in both first-line and maintenance therapy. It is also approved for the treatment of malignant pleural mesothelioma, often in combination with cisplatin. The drug works by inhibiting key enzymes involved in folate metabolism, which are essential for DNA and RNA synthesis, thereby preventing rapid cell division in cancer cells. To reduce toxicity, patients are typically supplemented with folic acid and vitamin B12 before treatment. Its use is generally limited to patients with adequate kidney function due to its route of elimination.