Raltitrexed (Thaltitrexed, Tomudex, TDX, ZD 1694) is an antimetabolite drug used in cancer chemotherapy.

[3][4] Raltitrexed is chemically similar to folic acid and is in the class of chemotherapy drugs called folate antimetabolites, which inhibit one or more of three enzymes that use folate and derivatives as substrates: DHFR, GARFT and thymidylate synthase.

Raltitrexed is fully active after polyglutamylation, which allows cellular retention of the drug.

By inhibiting Thymidylate synthase (TS), thus formation of precursor pyrimidine nucleotides, raltitrexed prevents the formation of DNA and RNA, which are required for the growth and survival of both normal cells and cancer cells.

Inhibition of L1210 cell growth in culture IC50 = 9 nM, is one of the strongest antimetabolites in use.