Germ cell development over a 28-d exposure window and 70-d treatment-free periods accounts for the spermatogenic cycle kinetics in rats and maximizes exposure in undifferentiated spermatogonia (stem cells). The full line denotes the developmental trajectory of spermatogonia that received a full 28-d exposure to molnupiravir into sperm that were collected from the cauda epididymis at the end of the treatment-free period.