A controlled-release formulation of the 5-hydroxytryptamine 3 (5-HT3) antagonist granisetron, in which granisteron is encapsulated in a biodegradable poly(ortho ester) polymer, with antiemetic activity. Upon subcutaneous administration, APF530 slowly erodes and releases the active ingredient granisetron over a period of approximately 5 days. As a selective serotonin receptor antagonist, granisetron competitively blocks the action of serotonin at 5-HT3 receptors, resulting in the suppression of nausea and vomiting.