Trimethoprim-d₃is intended for use as an internal standard for the quantification of trimethoprim by GC- or LC-MS. Trimethoprim is a synthetic antibiotic that inhibits dihydrofolate reductase (DHFR), which is necessary for the synthesis of purines, amino acids, and thymidylic acid.^1,2Trimethoprim shows prominent selectivity for bacterial DHFR over mammalian DHFR (IC₅₀s = 5 and 30,000 nM, respectively).²Formulations containing trimethoprim, commonly used in combination with sulfamethoxazole to minimize acquired resistance, have been used in the treatment of urinary tract infections.

1.Lam, T., Hilgers, M.T., Cunningham, M.L., et al.Structure-based design of new dihydrofolate reductase antibacterial agents: 7-(Benzimidazol-1-yl)-2,4-diaminoquinazolinesJ. Med. Chem.57(3)651-668(2014) 2.Schweitzer, B.I., Dicker, A.P., and Bertino, J.R.Dihydrofolate reductase as a therapeutic targetFASEB J.4(8)2441-2452(1990)