<p>Pemetrexed is a thymidylate synthase inhibitor. It works by inhibiting thymidylate synthase, dihydrofolate reductase, glycinamide ribonucleotide formyltransferase and aminoimidazole carboxamide ribonucleotide formyltransferase, the enzymes involved in folate metabolism and DNA synthesis, thus inhibiting purine and thymidine nucleotide and protein synthesis.</p>