Big Blue^® Transgenic Rat Gene Mutation Assay in somatic cells after 28-d treatment with molnupiravir. Mutation frequency in bone marrow (a) and mutation frequency in liver cells (b). The dotted line represents the upper 95% CL of the historical vehicle control study mean distribution. Positive control: ENU 20 mg/kg administered on 6 nonconsecutive days (ENU); *P ≤ 0.05. CL, confidence limit; ENU, N-Nitroso-N-ethylurea; HC, historical control; PC, positive control.