Final answer:
A sponsor has 15 calendar days to report a fatal or life-threatening unexpected adverse drug reaction according to FDA regulations.
Step-by-step explanation:
According to FDA regulations, a sponsor has 15 calendar days to report a fatal or life-threatening unexpected adverse drug reaction. This means that from the time they become aware of the event, they must submit the report within 15 days. However, it is important to note that other events should be reported on a quarterly basis.