Antiemetics:

Are drugs used to prevent or treat nausea and vomiting.
Nausea is an unpleasant sensation of abdominal discomfort accompanied by a desire to vomit.
Vomiting is the expulsion of stomach contents through the mouth Nausea may occur without
vomiting and vomiting may occur without prior nausea, but the two symptoms most often occur
together.
93

• Vomiting occurs when the vomiting center in the medulla oblongata is stimulated.
  Dopamine and acetylcholine play a major role in stimulating the vomiting center. To a
  certain extent, vomiting is a protective mechanism which can result from various noxious
  stimuli.
  Drugs used in nausea and vomiting belong to several different therapeutic classifications.
• Most antiemetic agents relieve nausea and vomiting by acting on the vomiting center,
  CTZ, cerebral cortex, vestibular apparatus, or a combination of these.
• Antiemetic drugs are generally more effective in prophylaxis than treatment. Antiemetic
  drugs include:
  Phenothiazines (neuroleptics) such as chlorpromazine
• Acts on CTZ and vomiting center
• Block dopamine receptors
• Are effective in prevention or treating nausea and vomiting induced by drugs, radiation
  therapy, surgery and most other stimuli
  (e.g. pregnancy).
• Are generally ineffective in motion sickness.
  Antihistamines – such as promothazine, dimehydrinate etc.
• Are especially effective in prevention and treatment of motion sickness (but they may
  cause concurrent drowsiness, that may be troublesome for travellers)
  Miscellaneous antiemetics
  Metoclopramide has both central and peripheral antiemetic effects. Centrally, metoclopoamide
  antagonizes the action of dopamine.
  Peripherally metoclopoamide stimulates the release of acetylcholine, which in turn, increases
  the rate of gastric emptying (used in esophapeal reflux)
  Indication as chlorpromazine
• Scopolamine, an anticholinergic drug is very effective in reliving nausea & vomiting
  associated with motion sickness.
• Ondansetron- is serotonin antagonist (5-HT3 receptors) found on the afferent fibers of the
  vagus nerve and in parts of the brain associated with CTZ.
• Controls chemical induced vomiting and nausea)
  V. Drugs used to induce vomiting
  In case of poisoning with noncorrosive agents, and assuming incomplete absorption of the
  poison has taken place, induction of vomiting can be carried out
  The drug used for this purpose is emetine, the active ingredient of ipecacuanha (syrup of
  ipecac).
  Emetine induces by direct irritation of the upper gut and on absorption, it also acts on CTZ.
  Drugs used in the treatment of haemorrhoids
  Haemorrhoids are varicose veins of the anal canal which can be very distressing for the
  sufferer. There is no pharmacological cure for this disorder, which is often self-limiting, if not,
  may require surgical intervention.
  The use of drugs may however, linder the sufferings:
• Stool softeners may alleviate constipation; lessen straining which can worsen the
  condition.
• Local anesthetics (e.g. lignocaine, benzocaine) relieve pain
• Corticosteroids (e.g. predniosolone) suppress inflammation, itching & swelling
• Vasoconstrictors (e.g. adrenaline, phenylephine) lessen venous swelling
• Astringent compounds (e.g. tannic acid) reduce swelling by precipitating cell surface
  proteins. Antihaemmorhoidal preparations contain one or more of these agents.