Emesis phenothiazines

A variety of drugs that block DA receptors are available for clinical use, and even more for experimental purposes. These drugs, also referred to as neuroleptics, include phenothiazines (e.g., chlorpromazine), thioxanthenes (e.g., chlorprothixene), butyrophenones (e.g., haloperidol), diphenylbutylpiperidines (e.g., pimozide), and dibenzodiazepines (e.g., clozapine). The major medical applications for these drugs are in the treatment of severe psychiatric illnesses, certain movement disorders, emesis and intractable hiccough. 

Emesis. BA receptor blocking agents suppress nausea and vomiting. Phenothiazines, such as chlorpromazine and prochlorperazine, are usually employed. Their action is probably mediated via blockade of BA receptors in the chemoreceptor trigger zone of the medulla oblongata. 

The nausea and vomiting associated with chemicophysical agents that stimulate the chemoreceptor trigger zone for emesis are best treated with a phenothiazine derivative. With the exception of thioridazine (Mellaril), aU have antiemetic effects, and the ones most often used are ... 

Phenothiazine derivatives depress the chemoreceptor trigger zone for emesis, and large doses also inhibit the vomiting center. It has been reported that thiethylperazine depresses both the chemoreceptor trigger zone and the vomiting center (see Figure 73). 

Radiation-induced emesis, or uncontrolled vomiting in patients undergoing radiation therapy, may necessitate either discontinuation of the treatment or prophylactic treatment with phenothiazine antiemetics. 

Postoperative nausea and vomiting are directly related to the type and dose of the anesthetic used. It has been shown that the use of a muscle relaxant, which substantially reduces the amount of anesthetic needed, lessens the incidence and intensity of postoperative nausea and vomiting. Flowever, most of the phenothiazines may be used to control postoperative emesis. 

Phenothiazines such as prochlorperazine, thiethylperazine, and chlorpromazine see Chapter 18) are among the most commonly used antinauseants and antiemetics. Their principal mechanism of action is dopamine receptor antagonism at the CTZ. Compared to metoclopramide or ondansetron see above), these drugs do not appear to be as uniformly effective in cancer chemotherapy-induced emesis. On the other hand, they also possess antihistaminic and anticholinergic activities, which are of value in other forms of nausea, such as motion sickness. 

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