Difference between emetinics and antiemetinics
Answers
Answer: Emetics and antiemetics
1. Dr. D. K. Brahma Associate Professor Department of Pharmacology NEIGRIHMS, Shillong
2. Emetic Response: Relaxation of fundus, body of stomach and also the oesophageal sphincter and oesophagus – but contraction of pylorus and duodenum – then rythmic contraction of diaphragm and abdominal muscles - expulsion via mouth Centre: Medulla Oblongata Relay Centers: chemoreceptor trigger zone (CTZ) and nucleus tractus solitarius (NTS) Afferent impulses: GIT, throat and other viscera Triggering agents: Blood borne drugs, mediators, hormones and toxins etc. – clinically cytotoxic drugs and radiation Transmitter: 5-HT (enterochromaffin cells) – via 5HT3 receptor of ENS – to vagal and spinal visceral neurones ----- to CTZ and NTS Spilling of 5-HT due to massive release – acts on CTZ
3. Other mediators: H1, D2, 5HT3, Muscarinic M and opioid μ etc. – expressed in CTZ and NTS Vestibular apparatus: generates impulses ◦ Body equilibrium disturbed ◦ Ototoxic drugs Mainly relayed by cerebellum to vomiting centre – Muscarinic and H1 receptors Directly in higher centres: Bad smell, ghastly sight, pain, fear etc. – drug cisplatin
4. Drugs which induce vomiting Acts on CTZ: Apomorphine Acts reflexly and on CTZ: Ipecacuanha Apomorphine: Morphine derivative – semi-synthetic – Dopaminergic agonist in CTZ ◦ 6 mg IM/SC – acts within 5 minutes ◦ Respiratory depression ◦ Orally – not recommended (large dose – slow inconsistent) ◦ Parkinsonism Ipecacuanha: Cephaelais ipecacuanha ◦ Syrup ipecac – 15 to 30 ml (10 to 15 in child) ◦ Action takes 15 minutes ◦ MOA: Irritation of Gastric mucosa and directly on CTZ
5. Salt water • Warm water – mild emetic • 2 spoonful of common salt in 1 pint of warm water Mustard seed • 1 table spoonful ground mustard seeds in half-pin of warm water • Strong coffee is one of the best domestic stimulants, especially after a narcotic poison
6. In Corrosive poisoning – acid and alkali (why?) In CNS stimulant poisoning To unconscious patients In Morphine and Phenothiazine poisoning
7. 1. Anticholinergics: Hyoscine, Dicyclomine 2. H1 antihistaminics: Promethazine, Diphenhydramine, Doxylamine, Cyclizine, Meclizine and Cinnarazine 3. Neuroleptics (D2 blockers): Chlorpromazine, Prochlorperazine and Haloperidol 4. Prokinetics: Metoclopramide, Domperidone, Cisapride, Mosapride and Tegaserod 5. 5HT3 antagonists: Ondansetron, Granisetron 6. Others: Dexamethasone, Benzodiazepines and Cannabinoids 7. Newer Ones: NK1 receptor antagonist - Aprepitant
8. Hyoscine: Motion Sickness (0.2 to 0.4 mg IM) ◦ Used IM/SC, but short duration of action ◦ MOA: Blocking of cholinergic link of vestibular apparatus to the vomiting centre – does not work in vomiting due to other aetiology ◦ ADRs: Sedation, dry mouth and other anticholinergic effects ◦ Transdermal delivery system (1.5 mg) Dicyclomine: Prophylaxis of motion sickness and morning sickness
9. Primarily used in motion sickness, morning sickness and some other vomiting in lesser extent – also anticholinergic, antihistaminic and antidopaminergic actions Promethazine (Phenothiazine), diphenhydramine: 4 – 6 Hours protection ◦ Combined with metoclopramide in CINV: additive effect plus counters extra pyramidal effects Promethazine theoclate (Avomine) – motion sickness Doxylamine: Sedative H1 antihistaminic – marketed in combination with Pyridoxine – specifically for morning sickness – duration of action 10 Hours (at bed time) – drowsiness, dry mouth, vertigo Meclizine: Long duration of action – sea sickness Cinnarizine: anti vertigo action – inhibits Ca++ influx in endolymph
10. Motion Sickness: Anticholinergics are preferred – followed by H1 Antihistaminics – antidopaminergics do not work Morning Sickness: Preferably drugs should be avoided – reassurance and dietary modification ◦ Dicyclomine, promethazine or metoclopramide are preferred at low doses