Pemetrexed is chemically similar to folic acid and is in the class of chemotherapy drugs called folate antimetabolites. It works by inhibiting three enzymes used in purine and pyrimidine synthesis—thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT). By inhibiting the formation of precursor purine and pyrimidine nucleotides, pemetrexed prevents the formation of DNA and RNA, which are required for the growth and survival of both normal cells and cancer cells. Pemetrexed is also recommended in combination with carboplatin for the first-line treatment of advanced non-small cell lung cancer. However, the relative efficacy or toxicity of pemetrexed-cisplatin versus pemetrexed-carboplatin has not been established beyond what is generally thought about cisplatin or carboplatin doublet drug therapy.
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