Nosiheptide exhibits extremely potent activity against all contemporary Staphylococcus aureus strains tested including multiple drug-resistant clinical isolates, with MIC values ≤ 0.25 mg/L. Nosiheptide is also highly active against Enterococcus spp and the contemporary hypervirulent BI strain of Clostridium difficile but is inactive against most Gram-negative strains tested. Time-kill analysis reveals Nosiheptide to be rapidly bactericidal against Staphylococcus aureus in a concentration- and time-dependent manner, with a nearly 2-log kill noted at 6 hours at 10X MIC. Furthermore, Nosiheptide is found to be non-cytotoxic against mammalian cells at >> 100X MIC, and its anti- Staphylococcus aureus activity is not inhibited by 20% human serum. Notably, Nosiheptide exhibits a significantly prolonged post-antibiotic effect against both healthcare- and community-associated Staphylococcus aureus compared to vancomycin.

Nosiheptide (20 mg/kg; intraperitoneal injection; injected at 1 and 8 h post-infection; female CD1 mice) provids significant protection against mortality. Ten out of 10 of the Nosiheptide-treated mice remains alive on day 3, while 6/10 of the controls died on day 1.