SANCUSO transdermal patch is indicated in adults for the prevention of nausea and vomiting caused by chemotherapy. It contains granisetron as the active ingredient. The patch is usually applied 24 to 48 hours before chemotherapy begins and should be left in place for at least 24 hours after chemotherapy, but should not be worn continuously for longer than a total of 7 days.

a) Explain why the patch should be applied 24 to 46 hours before chemotherapy. (2 marks)

Transdermal delivery system drug release and drug absorption into the body is gradual, and it takes at least 24 hours for effective blood levels of drug to be reached.