Pig-a mutation assay in rats after 28-d treatment with molnupiravir. Mutation frequency in reticulocytes (a) and mutation frequency in red blood cells (b). Positive control: ENU 20 mg/kg administered on 6 nonconsecutive days; *P ≤ 0.05. Dotted line represents upper 95% CL of the historical vehicle control study mean distribution. CL, confidence limit; ENU, N-Nitroso-N-ethylurea; HC, historical control; PC, positive control.