Trimetrexate (CI-898) is an antibiotic, also a potent and orally active dihydrofolate reductase (DHFR) inhibitor, reducing the production of DNA and RNA precursors and leading to cell death, with IC50 values of 4.74 nM and 1.35 nM for human DHFR and Toxoplasma gondii DHFR. Trimetrexate can also inhibit the growth of various cancer cells. Trimetrexate can be used for researching Pneumocystis carinii pneumonia (PCP) and cancer[1][2][3][4][5].