Which of the following is NOT a centrally acting antiemetic?

Adsorbents are not classified as centrally acting antiemetics. These agents, such as activated charcoal and certain over-the-counter medications, work by binding to toxins and substances in the gastrointestinal tract, thereby preventing their absorption into the body. They are primarily utilized for their ability to adsorb various substances, including some drugs and toxins, rather than exerting a direct effect on the central nervous system (CNS) to control nausea and vomiting.

In contrast, centrally acting antiemetics like prochlorperazine, dimenhydrinate, and ondansetron interact with receptors in the brain to alleviate nausea. Prochlorperazine is a phenothiazine that blocks dopamine receptors in the CTZ (chemoreceptor trigger zone), while dimenhydrinate is an antihistamine that has anticholinergic properties, affecting the vestibular system. Ondansetron is a serotonin 5-HT3 receptor antagonist that works by blocking the signals that trigger nausea and vomiting in the CNS. Each of these medications has a specific mechanism of action that targets neurotransmitters in the brain, differentiating them from adsorbents, which act locally within the gastrointestinal tract.