Fanotaprim is a dihydrofolate reductase (DHFR) inhibitor. Fanotaprim inhibits the growth of T. gondii strains with a TgDHFR IC50 of 1.57 ± 0.11 nM and a hDHFR IC50 of 308 ± 71 nM and a hDHFR to TgDHFR selectivity ratio of 196.

TgDHFR:1.57 ± 0.11 nM(Toxoplasma gondii), DHFR (human):308 ± 71 nM(human)

Fanotaprim had a parasiticidal EC50 of 13 nM against the type I RH strain of T. gondii. In human MCF-7 cells, Fanotaprim had an EC50 value of 7300 nM. The selectivity of Fanotaprim in the cell-based assays is in line with its DHFR selectivity profiles of 200-fold[1].

Fanotaprim had moderate mouse liver microsome (MLM) intrinsic clearance (Clint) of 56.3 mL min–1 kg–1, which is 63% of mouse liver blood flow (LBF). Fanotaprim has low to moderate clearance of 10.6 mL min–1 kg–1, a volume of distribution of 1.14 L/kg, and a half-life of 3.9 h after a 1.0 mg/kg, iv dose. Oral bioavailability after a 0.83 mg/kg po dose was 47.3% with a Cmax of 178 ng/mL 30 min after dosing. The unbound fraction (%) in mouse plasma is 8.7 ± 0.2 and in brain homogenate 2.4 ± 0.3, determined using an equilibrium dialysis method. Fanotaprim was freely permeable into the mouse CNS at 0.5 h after a 10 mg/kg oral dose; the concentration in brain was 2560 ± 240 ng/g and in blood 1610 ± 580 ng/mL, giving a brain to blood ratio of 1.7 ± 0.6[1].