Antiemetic pharmacology and classification are fundamental aspects of understanding how drugs are used to manage nausea and vomiting, common symptoms in various medical conditions. Antiemetics encompass a diverse group of medications that play a crucial role in providing relief to patients. These drugs are classified into several categories based on their mechanisms of action and target receptors. One important class of antiemetics is serotonin antagonists, which work by blocking serotonin receptors in the gastrointestinal tract and the central nervous system. Dopamine antagonists, on the other hand, target dopamine receptors and are particularly effective in preventing chemotherapy-induced nausea and vomiting. Antihistamines, often used for motion sickness, act on histamine receptors, while corticosteroids have broad anti-inflammatory effects and are employed in various situations where nausea and vomiting are problematic. NK1 receptor antagonists are newer additions to the antiemetic arsenal and specifically target substance P receptors. Lastly, cannabinoids, derived from cannabis, have gained attention for their potential antiemetic properties. Understanding the pharmacological mechanisms and classifications of these antiemetic drugs is essential for healthcare professionals to select the most appropriate treatment for their patients, tailored to the underlying cause and individual needs.
2. EMESIS
🌷 It is protective mechanism which serves to eliminate harmful substances from the
stomach.
🌷 Occurs due to stimulation of the emetic center situated in the medulla oblongata.
🌷 Multiple pathways can rlicit vomiting.
🌷 CTZ and NTS are the most important relay areas for afferent impulsesarisibg from
GIT, throat and other viscera.
🌷 CTZ also accessible to blood borne drugs, mediators, hormones, toxins, etc.
3. 🤮 EMETICS 🤮
🌼 These are the drugs which are used to evoke vomiting.
1️⃣ Centrally acting – Apomorphine ( directly stimulate the CTZ or VC )
2️⃣ Peripherally acting – mustard , potassium tartrate, and hypertonic NaCl (
concentrated solutions )
3️⃣ Both – Ipecacuanha ( stimulate the VC by irritating gastric & duodenal mucosa
which stimulate afferent fibres of vagus nerve)
4. 👉🏻 Apomorphine 💉
✏️ Semi synthetic derivative of morphine.
✏️ Given IM or SC, acts centrally.
✏️ Dose is 6 mg ( 2-8 mg )
✏️ Induces vomiting in 5-10 minutes.
✏️ Not given if respiration is depressed.
👉🏻 Ipecacuanha 🧂
✏️ Contains two alkaloids – emetine &
cephaeline .
✏️ Used as syrup ipecac.
✏️ Produces effect in 15 minutes.
✏️ Acts by irritating gastric mucosa & through
CTZ centre.
✏️ Dose – 5 ml in infants, 10-15 ml in children,
15-20 in adults.
6. 🤮 INTRODUCTION – ANTI EMETICS
🌿 Two Centres
- Vomiting Centre (VC)
- Chemoreceptor trigger zone (CTZ)
🌿 Both near to the floor of the fourth ventricle, close to the vital centres.
🌿 VC is within the BBB
🌿 CTZ outside in the area postrema & they both are connected together.
🌿 Def. - A group of drugs which are used to control the nausea and vomiting.
10. 1. ANTICHOLINERGICS
👉🏻 HYOSCINE –
• 0.2 – 0.4 mg oral, i.m.
• Most effective for motion sickness
• Brief duration of action – produce sedation, dry mouth and anticholinergic side
effects.
👉🏻 DICYCLOMINE –
• 10-20 mg oral
• Prophylaxis of morning & motion sickness
11. 🍁H-1 ANTIHISTAMINICS🤮
• Some antihistaminics are antiemetic like promethazine, diphenhydramine,
dimenhydinate.
• They protect from motion sickness for 4-6 hours.
• Produce sedation & dryness of mouth so driving should not be proceede after having
these drugs.
• Combination of these with other antiemetics has been used in chemotherapy-
induced nausea and vomiting (CINV)
12. 🍁NEUROLEPTICS🤮
• The older neuroleptics ( phenothiazines, haloperidol) are potent antiemetics and
sedative.
• They act by blocking D2 receptors in the CTZ; antagonize apomorphine induced
vomiting.
👉🏻 Useful in –
- Drug induced vomiting
- Post operative nausea and vomiting
- Radiation sickness vomiting
13. 🍁PROKINETIC DRUGS 💉
• These drugs promote GIT transit and speed gastric emptying by rnhancing
coordinated propulsive motility.
• They acts through both dopaminergic and serotonergic receptors.
• D-2 antagonism
• 5-HT3 agonism
• Sedation, dizziness, loose stools, muscle dystonias are the main side effects.
• Long term use can cause parkinsonism, galactorrhoea and gynaecomastia.
14. 🍁5 – HT3 ANTAGONISTS 💊
• Ondansetron is prototype developed to control cancer chemotherapy induced
vomiting.
• Cytotoxic drugs produces nausea & vomiting by causing cellular damage, which
releases mediators including 5- HT from intestinal mucosa resulting in transmission
of impulses to the NTS and CTZ.
• Oral bioavailability of ondansetron is 60-70 % due to first pass metabolism.
• Elimenated by urine and faeces t1/2 is 3-5 hrs.
