Final answer:
Sponsors must report unexpected serious or fatal adverse drug events to the FDA within 15 days, and submit other adverse drug experiences on a quarterly basis. The FDA also accepts spontaneous reports through the MedWatch program.
Step-by-step explanation:
When an incident, such as an unexpected serious or fatal adverse drug event, occurs, the sponsor must report it to the FDA within 15 days. These are high-priority incidents that require prompt attention to ensure public safety and regulatory compliance. For other, less critical adverse drug experiences, reports should be made on a quarterly basis. Additionally, the FDA receives voluntary reports through its MedWatch program, which are referred to as 'spontaneous reports' because they are not mandatory and rely on the initiative of consumers and health professionals.