Assistant Professor Dr. Shamil AL-Neaimy Antiemetic drugs Assistant Professor Dr. Shamil AL-Neaimy

Vomiting : is a protective mechanism to remove harmful or irritant substances from upper GIT , controlled by vomiting center in medulla that receive stimuli from :

1-Chemoreceptor trigger zone ( CRTZ). 2-Vestibular system . 3-Periphery : Distension of gut or biliary tract or renal colic or MI . Vomiting center contains M-receptors , H1-receptors & dopamine ( D2)-receptors.

Drugs : 1-Anticholinergic : Hyosine or Scopolamine (Atropine) 2-H1-blockers: Cyclizine , Meclizine , Diphenhydramine, dimenhydrinate , promethazine

3-Dopamine ( D2) antagonists: -Metoclopramide ( plasil) , Domperidone (CRTZ , gut). -Haloperidol (CRTZ). -Chlorpromazine(largactil), Promazine , prochlorperazine (Stemetil) (CRTZ,vomiting center)

4-5-HT3-Blockers : Ondansetron, Tropisetron & granisetron. 5-Others : Dexamethasone , methylprednisolone , Diazepam & lorazepam.

Prokinetics(drugs promoting GIT motility ) : 1-Metoclopramide (plasil): Antiemetic , prokinetic , blocks dopamine receptors in CRTZ , enhances actions of Ach on M-receptors in GIT, elevates the tone of lower esophageal sphincter, increasing peristalsis & emptying upper GIT , it also stimulates prolactin secretion leading to galactorrhea .

Indications: Nausea , vomiting , pre-anesthesia , GERD , radiotherapy , endoscopy & migraine . Side effects : -extrapyramidal dystonia , torticollis , Parkinsonism , gynaecomastia & lactation .

Oculogyric crisis : Oculogyric Crisis usually occurs as a side effect of neuroleptic drug treatment. It is one of the acute dystonic reaction(torticollis & blepharospasm) , treated by procyclidine or diphenhydramine & diazepam . Drug interactions: Atropine(anti-M) as it enhances the action of Ach on M-receptors .

2-Domperidone : Dopamine antagonist, antiemetic , prokinetic 2-Domperidone : Dopamine antagonist, antiemetic , prokinetic . Indications: Nausea & vomiting of cytotoxic therapy . Side effects : Dystonia ( less than plasil) , gynaecomastia & lactation .

3-Cisapride : prokinetic , It is not dopamine antagonist but related to plasil . withdrawn from the market because it causes serious arrhythmias. Indications: GERD . Side effects : cramps & diarrhea . 4-Erythromycin : antibiotic & prokinetic . 5-Bethanechol : cholinomimetic & prokinetic .

6. Substance P/neurokinin-1 receptor blocker: Aprepitant targets the neurokinin receptor in the brain and blocks the actions of the naturalsubstance. Aprepitant is usually administered orally with dexamethasone and palonosetron. It undergoes extensive metabolism.

Combination regimens dexamethasone, increase antiemetic activity when given with high-dose metoclopramide, a 5-HT3 antagonist, phenothiazine butyrophenone, a cannabinoid, or a benzodiazepine diphenhydramine, are often administered in combination with high-dose metoclopramide to reduce EP or with corticosteroids to counter metoclopramide-induced diarrhea.

Drugs used in treatment of motion sickness : Motion sickness : is a medical condition occurs due to over-stimulation of vestibular system or visual or environmental factors or due to moving horizontally or vertically .

Drugs: 1-Hyoscine ( atropine) . 2-Cyclizine & meclizine. 3-Diphenhydramine & dimenhydrinate . 4-promethazine . Drugs used to induce vomitting : In case of poisoning , vomiting is induced by : -Ipecac syrup -Apomorphine .