24.4 : 催吐剂和止吐剂：多巴胺受体拮抗剂

Vomiting is a distressing symptom often triggered by cancer chemotherapy.

Dopamine receptor antagonists are key antiemetics. They bind to dopamine receptors in the chemoreceptor trigger zone and prevent receptor-dopamine interaction. This inactivates the receptor and reduces signal transmission to the vomiting center.

Common dopamine receptor antagonists belong to phenothiazines, butyrophenones, thienobenzodiazepines, and benzamides.

Phenothiazines, like prochlorperazine and promethazine, are available as tablets, injectables, or suppositories. As they also block histamine and muscarinic receptors, they are effective for motion sickness and GI disorder-related emesis.

Butyrophenones, such as droperidol, are given intramuscularly or intravenously to control acute chemotherapy-induced emesis.

Thienobenzodiazepines, like olanzapine, inactivate both dopamine and 5HT₂ receptors, preventing delayed vomiting post-chemotherapy.

Benzamides comprise metoclopramide, which inhibits vomiting and treats gastroparesis by increasing GI tract motility.

Adverse effects of these drugs include sedation, hypotension, dystonia, and cardiac arrhythmias.