Which of the following is NOT an anti-emetic listed in the provided information?

Metoclopramide is an important drug in the management of nausea and vomiting; however, in the context of the question regarding which option is NOT an anti-emetic, the identification of this particular drug as a correct answer may arise from its primary uses rather than its anti-emetic properties.

Metoclopramide functions as a prokinetic agent, enhancing gastrointestinal motility. While it does exert anti-emetic effects through its action on the central nervous system and peripheral receptors, its use is often more associated with addressing conditions like gastroparesis or as part of the preoperative management of patients rather than as a first-line anti-emetic during procedural sedation.

In contrast, ondansetron hydrochloride, prochlorperazine, and droperidol are primarily recognized as anti-emetic agents, frequently employed to prevent nausea and vomiting resulting from various triggers, including chemotherapy, anesthesia, and motion sickness. They have established protocols for usage specifically to combat nausea and vomiting, which clearly distinguishes them from metoclopramide in this regard in the scope of the question provided.