Trifluridine (Trifluorothymidine; 5-Trifluorothymidine; TFT) is an irreversible thymidylate synthase inhibitor, and thereby suppresses DNA synthesis. Trifluridine is an antiviral drug for herpes simplex virus (HSV) infection. Trifluorothymidine also has anti-orthopoxvirus activity.