In vitro activity and in vivo efficacy of sulopenem against Bacillus anthracis in inhalational anthrax mouse and rabbit models.

Bacillus anthracis is a gram-positive, spore-forming bacterium and the etiological agent of anthrax. As a Tier 1 Select Agent, the pathogen can be isolated from the natural environment, and the endospore is a significant biological threat that can be produced in large quantities, stored, and disseminated by aerosolization. The intentional release of B. anthracis spores has the potential for mass casualties and is a serious threat to public and military health. Fluoroquinolones and tetracyclines are common antibiotics used for post-exposure prophylaxis and treatment in the United States (U.S.), whereas penicillin is the drug of choice throughout the rest of the world. However, these commonly used antibiotics may be contraindicated or suboptimal in a public health crisis. Thus, there is a need for novel medical countermeasures to be developed and tested against B. anthracis. Sulopenem is a broad-spectrum, orally bioavailable penem antibiotic recently approved in the U.S. for the treatment of uncomplicated urinary tract infections in women with limited therapeutic options. Here, we demonstrate that sulopenem has potent in vitro activity against both wild-type virulent B. anthracis strains, as well as biosafety level 2 surrogate strains resistant to current standards of care. Using human-equivalent dosing regimens, we show that sulopenem is highly protective in both the mouse and rabbit inhalational anthrax models. Together, these results support continued evaluation of this oral penem as a countermeasure for inhalational anthrax.