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Although you can comment on any guidance at any time (see 21 CFR 10.115(g)(5)), to ensure that the FDA considers your comment on a draft guidance before it begins work on the final version of the guidance, submit either online or written comments on the draft guidance before the close date.
If unable to submit comments online, please mail written comments to:
Food and Drug Administration
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All written comments should be identified with this document's docket number: FDA-2022-D-0113
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Guidance Issuing OfficeCenter for Drug Evaluation and Research
This guidance describes the FDA’s recommendations regarding clinical pharmacology considerations for conducting human radiolabeled mass balance studies of investigational drugs, including: (1) deciding whether and when to conduct the study, (2) designing the study, and (3) reporting results. This guidance does not cover animal mass balance studies, safety testing of drug metabolites, or recommendations for selecting the radioactive dose.