A 56-year-old lady diagnosed with colorectal cancer underwent a left hemicolectomy. She was started on opioid analgesics in the postoperative period. She is suffering from postoperative nausea and vomiting and is unable to tolerate oral medications or fluids. 

(a)   Name THREE classes of antiemetic agents. (3 marks)

(b)   Explain the mechanism of action of metoclopramide. (2 marks)

(c) What are the side effects of metoclopramide? In what conditions is metoclopramide contraindicated? (6 marks)

(d)   What is the mechanism of action of prochlorperazine as an anti-emetic? (2 marks)

(e)   Name THREE drugs that may interact with prochlorperazine. (3 marks)

(f)    Explain the mechanism of action ondansetron. (2 marks)

(g)    What are the potential adverse effects of ondansetron? (2 marks)