Phenothiazines antiemetic action

Use cautiously in people with acute or chronic respiratory impairment, particularly children, because phenothiazines may suppress the cough reflex. If hypotension occurs, epinephrine is not recommended because phenothiazines may reverse its usual pressor effect and cause a paradoxical further lowering of blood pressure. Because these drugs have an antiemetic action, they may obscure signs of intestinal obstruction, brain tumor, or overdosage of toxic drugs. 

A number of the antihistamines, particularly the phenothi-azines and aminoalkyl ethers, have antiemetic actions and thus may be u.seful in the treatment of nausea, vomiting, and motion sickness. Also, those agents that produce pronounced. sedation have application as nonpiescription sleeping aids." - "Several of the phenothiazines have limited u.se in Parkinson-like syndromes as a result of their ability to block central muscarinic receptors." -And. a number of antihistamines, including promethazine, pyrilamine. tri-pelennamine and diphenhydramine, display local anesthetic activity that may be therapeutically useful. ... 

Nonpsychiatric indications With the exception of thioridazine, most phenothiazines have antiemetic actions prochlorperazine is promoted solely for this indication. Hj receptor blockade, mosi often present in short side-chain phenothiazines, provides the basis for their use as antipruritics and sedatives and contributes to their antiemetic effects. 

Mechanism of Action A phenothiazine that blocks dopamine neurotransmission at postsynaptic dopamine receptor sites. Possesses strong anticholinergic, sedative, and antiemetic effects moderate extrapyramidal effects and slight antihistamine action. Therapeutic Effect Relieves nausea and vomiting improves psychotic conditions controls intractable hiccups and porphyria. 

Mechanism of Action A phenothiazine that antagonizes dopamine neurotransmission at synapses by blocking postsynaptic dopaminergic receptors in the brain. Therapeutic Effect Decreases psychotic behavior. Also produces weak anticholinergic, sedative, and antiemetic effects and strong extrapyramidal effects. Pharmacokinetics Erratic absorption. Protein binding greater than 90%. Metabolized in liver. Excreted in urine. Half-life 33 hr. 

Mechanism of Action A phenothiazine that acts as an antihistamine, antiemetic, and CNS-antipsychotiC typical hypnotic. As an antihistamine, inhibits histamine at histamine receptor sites. As an antiemetic, diminishes vestibular stimulation, depresses labyrinthine function, and acts on the chemoreceptor trigger zone. As a sedative-hypnotic, produces CNS depression by decreasing stimulation to the brainstem reticular formation. Therapeutic Effect Prevents allergic responses mediated by histamine, such as rhinitis, urticaria, and pruritus. Prevents and relieves nausea and vomiting. Pharmacokinetics ... 

Mechanism of Action A phenothiazine derivative that blocks dopamine at postsynap-tic receptor sites. Possesses strong extrapyramidal and antiemetic effects and weak anticholinergic and sedative effects. Therapeutic Effect Suppresses behavioral response in psychosis reduces locomotor activity and aggressiveness. Pharmacokinetics Readily absorbed following PO administration. Protein binding 90%-99%. Metabolized in liver. Excreted in urine. Half-life 24 hr. 

Haloperidol blocks dopamine receptors in the brain and hence produces a very high incidence of movement disorders such as parkinsonism (see phenothiazine derivatives). Its mechanism of action in Gilles de la Tourette s syndrome is unknown. In addition to blocking dopamine receptors, haloperidol has many other central and peripheral effects it has weak peripheral anticholinergic and antiemetic... 

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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