Antiemetics Drugs - Classification, Mechanism of action, Indications, Contraindication, Adverse effects and Drug interactions



Antiemetics are the Drugs which prevents or control the Vomiting/Nausea.


5HT3 Antagonists – Ondansetron, Granisetron, Dolasetron.

Prokinetics / Dopamine Antagonists - Domperidone, Olanzapine, Metoclopramide

Antihistamines – Cyclizine, Diphenhydramine, Meclozine, Promethazine, Hydroxyzine.

Anticholinergics - HydroxyzineHyoscine & Dicyclomine.

Mechanism of action

5HT3 Antagonists They block serotonin receptors in CNS and Gastrointestinal tract so they can be used to treat post-operative cytotoxic (Chemotherapy) drugs nausea/ vomiting.

Prokinetics (Dopamine Antagonists): They block The Dopamin neurotransmitter also they promote gastrointestinal motility & quicken gastric emptying.

Antihistamines: They block the histamine neurotransmitter and they act by an effect on vomiting center and by producing sedative effect.

Anticholinergics: An Anticholinergic agent block the neurotransmitter Acetyl choline in central and peripheral nervous system.

Durgs and their Dosage

1 Hyoscine - 200-600mg (SC)

2 Diclomine - 40mg 6hourly

3 Cyclizine - 50mg 4-6 hour

4 Meclizine - 25mg/day

5 Metoclopramide - 10mg

6 Domperidone - 10-20 mg 4-6hours

7 Ondansetron - 8-16mg

Indications / Uses

5HT3 antagonists are used in management of nausea vomiting associated with chemotherapy.

Antihistamine such as diphen hydramine is used for motion sickness and morning sickness.

Metoclopramide is used for gastric emptying in patient’s receiving tube feeding.

Anticholinergic such as hyoscine, Dicyclomine are useful in travel sickness.

Contraindication / Precautions

Diphenhydramine is contraindicated in hypertensive patients.

Metoclopramide is contraindicated in suspected gastrointestinal problem.

Use cautiously and reduced dose in renal impairment conditions.

Adverse effects



Dryness of mouth.

Blurred vision.

Pain in IM injection site.


Rectal irritation.

Photo sensitivity reaction.

Drug interactions

Use antihistamine, other CNS depressants including opioids and sedative -hypnotic drugs causes additive CNS depression.

Metoclopramide affects GI motility and alter GI absorption of other drugs such as salicylates, levodopa, diazepam, lithium, and tetracycline.

Antiemetics Drugs Notes PDF

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