Determining the Relationship Between Clofazimine Gastrointestinal Levels and anti‐CryptosporidiumEfficacy in Mice

Introduction Cryptosporidiosis, the disease caused by parasitic infections with Cryptosporidium spp. can cause long‐term adverse impacts and even death in malnourished children and immunocompromised patients. The only FDA‐approved drug for treating cryptosporidiosis, nitazoxanide, has limited efficacy in the populations that are impacted most by the disease. A large‐scale phenotypic screening campaign identified clofazimine as active in both in vitro and in vivo preclinical models of Cryptosporidium infection. However, clofazimine was not effective in controlling Cryptosporidium infection in a subsequent Phase 2a clinical trial in HIV‐positive adults with cryptosporidiosis. Our recent pharmacokinetic/pharmacodynamic (PK/PD) modeling work demonstrated that plasma clofazimine levels observed in the Phase 2a clinical trial fell well below projected efficacious plasma concentrations estimated with preclinical in vivo data. Therefore, suboptimal clofazimine exposure in the Phase 2a trial likely contributed to the observed lack of efficacy. Nevertheless, plasma clofazimine levels may not represent local concentrations at the gastrointestinal (GI) tract, the site of action for treatment of Cryptosporidium infection. Thus, the objective of our current study is to build a physiologically based pharmacokinetic (PBPK) model of clofazimine in mice to simulate clofazimine GI pharmacokinetics (PK), estimate efficacious clofazimine concentrations at the tissue level, and explore important factors that can impact clofazimine exposure at the site of infection. Methods C57BL/6 mice were administered a single oral dose of clofazimine at dose levels ranging 0.03‐300 mg/kg. Blood samples were collected up to 240 hours post‐dosing and GI samples were collected at 240 hours post‐dosing. In tandem, an efficacy study treated C. parvum‐infected IFN‐γ‐/‐ mice with equivalent clofazimine dosing and oocysts in fecal samples were quantified over time. GastroPlus (Simulations Plus) was used for modeling and simulation. Results The final PBPK model captured clofazimine plasma PK in mice well across most doses (within a 2‐fold margin). The simulated clofazimine GI concentrations increased with increasing dose in a non‐proportional manner, similar to what was observed with the plasma PK. As expected for a drug with poor solubility, the non‐linearity was attributed to diminished drug dissolution at higher dose levels. The simulated clofazimine tissue concentrations were used to construct PK