Preferably we use both sexes. If you are looking for systemic toxicity, female rats are in most cases more susceptable than males.
@Lan Ma-Hock, thank you. I have seen many studies use male rats for sub-chronic studies and only female rats for acute toxicity study.I want to believe that there is nothing wrong in using only one sex for any of the studies provided the number of rats in each group exceed five. What do you think?
As Lan mentioned females are preferred spp as per OECD for Acute studies. However, for repeated dose systemic tox studies, equal no. of both sex is required as a general rule by most of regulatory agencies.
For Acute studies, selection of any one sex with demonstrating less tolerability than other sex would be sufficient. Whereas, in subchronic non-regulatory studies, the sex with high or comparable systemic test item exposure would be of choice.
Please note that the regulatory studies should be in both the sexes.
For acute and sub-acute (2 weeks) toxicity/maximum tolerated dose studies, female mice are commonly used since they are more sensitive to chemicals than their male counterparts, and help detect any residual toxicities easily. For sub-chronic and chronic toxicities, two species (one rodent and one non-rodent) involving both sexes should be used.
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