ST-193 is a potent broad-spectrum arenavirus inhibitor; inhibits Guanarito, Junin, Lassa and Machupo virus with IC 50 values of 0.44, 0.62, 1.4 and 3.1 nM, respectively. In Vitro ST-193 inhibits LASV pseudotypes with an IC 50 of 1.6 nM. ST-193 inhibits pseudotypes generated with other arenavirus envelopes as well, including the remaining four commonly associated with hemorrhagic fever (IC 50 s for Junín, Machupo, Guanarito, and Sabiá were in the 0.2 to 12 nM range) but exhibits no antiviral activity against pseudotypes incorporating either the GP from the LASV-related arenavirus lymphocytic choriomeningitis virus or the unrelated G protein from vesicular stomatitis virus, at concentrations of up to 10 μM. MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo ST-193 is found to be tolerated well when administered daily as an intraperitoneal injection of either 25 or 100 mg/kg/day for 14 days. ST-193-treated animals exhibit fewer signs of disease and enhance survival when compared to the ribavirin or vehicle groups. Body temperatures in all groups are elevated by day 9, but returned to normal by day 19 postinfection in the majority of ST-193-treated animals. ST-193 treatment mediates a 2- to 3-log reduction in viremia relative to vehicle-treated controls. The overall survival rate for the ST-193-treated guinea pigs is 62.5% (10/16) compared with 0% in the ribavirin (0/8) and vehicle (0/7) groups. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:IC50: 0.44 nM (Guanarito), 0.62 nM (Junin), 1.4 nM (Lassa) and 3.1 nM (Machupo)