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ANTI EMETICS
RVS Chaitanya
Koppala
Nausea and vomiting are thought to be protective reflexes
that serves to rid the gastrointestinal tract of toxic substances
They are symptoms of altered functions but are not diseases
Nausea denotes the feeling of impending vomiting, whereas
vomiting refers to the forceful expulsion of contents of
stomach and upper intestinal tract through the mouth
Retching is the labored rhythmic respiratory activity which
usually precedes vomiting
MECHANISM OF
VOMITING
Controlled by vomiting centre in the medulla
Stimuli are relayed to this centre from peripheral areas. i.e gastric
mucosa and other parts of GIT.
Sensory stimuli also arise within the central nervous system itself
i.e cerebral cortex and vestibular apparatus and the impulses are
transmitted to the vomiting centre
The lack of BBB at the chemoreceptor trigger zone (CTZ) (so
what )
Nausea and vomiting may be the symptoms of pregnancy or
infections, drugs, radiation, painful stimuli, metabolic and
emotional disturbance or due to travel sickness
The main neurotransmitter involved in the control of vomiting
are acetylcholine , histamine, 5-hydroxytryptamine and
dopamine
EMETICS
The drugs that produce vomiting are called as emetics
MUSTARD and COMMON SALT act peripherally by irritating the
stomach and are used as household emetics
MORPHINE and APOMORPHINE are centrally acting emetics,
they induce by stimulating CTZ.
IPECAC is a safe emetic. It has both central and peripheral
actions.
Emetics are contraindicated in certain cases of poisoning.
Contraindication for the use of emetics are
Children
Comatose patients
Corrosive and caustic poisoning
CNS stimulant drug poisonin
Kerosene poisoning
Morphine and phenothiazine poisoning
ANTIEMETICS(CLASSIFICATION )
Classification:
Anticholinergics :Hyoscine, Dicyclomine
H1antihistaminics: Pro m e thazine , Diphenhydramine, Dimenhydrinate,
Doxylamine, Meclozine (Meclizine), Cinnarizine.
Neuroleptics: Chlorpromazine, (D2 blo cke rs) Triflupromazine,
Prochlorperazine, Haloperidol, etc.
Prokinetic drugs: Me to clo pram ide , Domperidone, Cisapride,
Mosapride, Itopride
5-HT3 antagonists: O ndanse tro n, Granisetron, Palonosetron,
Ramosetron
NK1receptorantagonists: Aprepitant, Fosaprepitant
Adjuvant antiemetics: Dexamethasone, Benzodiazepines, Dronabinol,
Nabilone
Emetics and Anti emetics
ANTICHOLINERGICS
Scopolamine is the drug of choice used to prevent motion sickness.
It blocks the afferent impulses to the vomiting centre by its
anticholinergic action.
Its sedative effect also contributes to its antiemetics effect
Scopolamine is not effective for other types of vomiting
Adverse effects:
Sedation,
Dryness of mouth
Blurred vision
Urinary retention
ANTIHISTAMINES (H1-
BLOCKERS)
H1 blockers are mainly useful for the prevention of motion
sickness.
They are also effective in morning sickness. Postoperative and
other types of vomiting
Dimenhydrinate, diphenhydramine, promethazine, cysclizine and
meclizine are some H1 blockers
These drug are having antihistaminergic, anti cholinergic, weak
antidopaminergic and sedative properties1
Antiemetics effect is due to sedative and central anticholinergic
Cyclizine and meclizine have less sedative effect and among the
antihistamine
Cyclizine has the shortest duration of action (8 hours) and Meclizine
has longest duration of action (24 hours)
Meclizine is used for sea sickness
Doxylamine is promoted in India for morning sickness
Cinnarizine is used as antivertigo drug
Uses: Motion sickness, morning sickness, drug induced,
postoperative, radiation sickness, cancer chemotherapy induced
vomiting
NEUROLEPTICS
The older neuroleptics (phenothiazines, haloperidol) are potent
antiemetics; act by blocking D2 receptors in the CTZ.
Antagonize apomorphine induced vomiting and have additional
antimuscarinic as well as H1antihistaminic property.
They have broad spectrum antiemetic action effective in:
Drug induced and postoperative nausea and vomiting (PONV).
Disease induced vomiting: gastroenteritis, liver disease, migraine
Malignancy associated and cancer chemotherapy (mildly emetogenic)
induced vomiting.
Radiation sickness vomiting (less effective).
Morning sickness: should not be used except in hyperemesis
gravidarum.
Neuroleptics are less effective in motion sickness: the vestibular
pathway does not involve dopaminergic link.
Acute muscle dystonia may occur after a single dose, especially in
children and girls.
The antiemetic dose is generally much lower than antipsychotic
doses.
These agents should not be administered until the cause of vomiting
has been diagnosed; otherwise specific treatment of conditions like
intestinal obstruction, appendicitis, etc. may be delayed due to
Prochlorperazine
This D2 blo cking phe no thiazine is a labyrinthine suppressant,
has selective antivertigo and antiemetic actions.
It is highly effective when given by injection in vertigo
associated vomiting, and to some extent in CINV.
Prochlorperazine is used as an antiemetic, but not as
antipsychotic.
Muscle dystonia and other extrapyramidal side effects are the
PROKINETIC DRUGS
These are drugs which promote gastrointestinal transit and
speed gastric emptying by enhancing coordinated propulsive
motility.
This excludes traditional cholinomimetics and anti-ChEs which
produce tonic and largely uncoordinated contraction.
Metoclopramide
Metoclopramide, a substituted benzamide, is chemically related
to procainamide, but has no pharmacological similarity with it.
Introduced in early 1970s as a ‘gastric hurrying’ agent, it is a
commonly used antiemetic.
Actions:
GIT:
Me to clo pram ide has m o re pro m ine nt e ffe ct on upper g.i.t.;
increases gastric peristalsis while relaxing the pylorus and the first
part of duodenum → speeds gastric emptying
This action is independent of vagal innervation, but is stronger
when vagus is intact.
Lower esophageal sphincter (LES) tone is increased and
gastroesophageal reflux is opposed.
It also increases intestinal peristalsis to some extent, but has no
significant action on colonic motility and gastric secretion.
CNS
Me to clo pram ide is an e ffe ctive antie m e tic; acting on the CTZ,
blocks apomorphine induced vomiting.
The gastrokinetic action may contribute to the antiemetic
effect.
However, it has no chlorpromazine (CPZ) like antipsychotic
property, though it does share the extrapyramidal and prolactin
secretion augmenting action of CPZ.
MECHANISM OF ACTION:
Metoclopramide acts through both dopaminergic and serotonergic
receptors
1. D2antagonism:
Do pam ine (acting thro ug h D2 receptors) is an inhibitory transmitter
in the g.i.t
Normally acts to delay gastric emptying when food is present in
stomach.
It also appears to cause gastric dilatation and LES relaxation
attending nausea and vomiting.
Metoclopramide blocks D2 receptors and has an opposite effect—
hastening gastric emptying and enhancing LES tone by augmenting
ACh release.
2. 5-HT4agonism
Me to clo pram ide acts in the g.i.t. to enhance ACh release from
myenteric motor neurones.
The g astric hurrying and LES to nic e ffe cts are mainly due to this
action which is synergized by bethanechol and attenuated by
atropine.
3. 5-HT3antagonism
At hig h co nce ntratio ns metoclopramide can block 5-HT3 receptors
present on inhibitory myenteric interneurones and in NTS/ CTZ.
The peripheral action can augment Ach release in the gut, but
appears to be minor.
The central anti 5-HT3 action appears to be significant only when
large doses are used to control CINV.
Adverse effects
Sedation,
dizziness,
loose stools,
muscle dystonias (especially in children).
Long-term use can cause parkinsonism, galactorrhoea and
gynaecomastia,
No harmful effects are known when used during pregnancy. Though
the amount secreted in milk is small, but suckling infant may develop
loose motions, dystonia, myoclonus.
Uses:
Antiemetic: Metoclopramide is an effective and popular drug for
many types of vomiting— postoperative, drug induced, disease
associated (especially migraine), radiation sickness, etc, but is less
effective in motion sickness.
Gastrokinetic:
(a) When emergency general anaesthesia has to be given and the
patient has taken food less than 4 hours before.
(b) To relieve postvagotomy or diabetic gastroparesis associated
gastric stasis.
(c) To facilitate duodenal intubation
Dyspepsia: and other functional g.i.t disorders. Metoclopramide may
succeed in stopping persistent hiccups
Gastointestinal reflux disease: Metoclopramide may benefit milder
cases of GERD, but is much less effective than PPIs/H2 blockers. It
does not aid healing of esophagitis, but may be used as adjuvant to
acid suppressive therapy
DOMPERIDONE
It is a D2 receptor antagonist, chemically related to haloperidol, but
pharmacologically related to metoclopramide.
Unlike metoclopramide, its prokinetic action is not attenuated by
atropine and is based only on D2 receptor blockade in upper g.i.t.
Domperidone crosses blood-brain barrier poorly. Accordingly,
extrapyramidal
Side effects are rare, but hyperprolactinaemia can occur. The
antiemetic action is exerted mainly through CTZ which is not protected
by blood-brain barrier.
CISAPRIDE
This benzamide derivative is a prokinetic with little antiemetic property,
because it lacks D2 receptor antagonism.
Effects of cisapride on gastric motility resemble metoclopramide, i.e.
gastric emptying is accelerated, LES tone is improved and esophageal
peristalsis is augmented
The prokinetic action is exerted mainly through 5-HT4 agonism which
promotes ACh release from myenteric neurones, aided by weak 5-HT3
antagonism which suppresses inhibitory transmission in myenteric
plexus.
Enteric neuronal activation via 5-HT4 re ce pto r also pro m o te s cAMP-
dependent Cl secretion in the colon, increasing water content of stools.
Safety of cisapride was challenged by reports of serious ventricular
arrhythmias and death, mainly among patient
5-HT3 ANTAGONIST
Ondansetron
Developed to control cancer chemotherapy/radiotherapy induced
vomiting, and later found to be highly effective in PONV and
disease/drug associated vomiting as well.
It blocks the depolarizing action of 5-HT exerted through 5-HT3
receptors on vagal afferents in the g.i.t. as well as in NTS and CTZ.
Cytotoxic drugs/radiation produce nausea and vomiting by causing
cellulardamage release of mediators including 5-HT fromintestinal→
mucosa activation of vagal afferents in the gut emetogenic→ →
impulses to the NTS and CTZ.
Ondansetron blocks emetogenic impulses both at their peripheral
origin And their central relay.
It does not block dopamine receptors.
Pharmacokinetics:
O ral bio availability o f o ndanse tro n is 60–70% due to first pass
metabolism.
It is hydroxylated by CYP1A2, 2D6 and 3A, followed by glucuronide
and sulfate conjugation.
No clinically significant drug interactions have been noted.
It is eliminated in urine and faeces, mostly as metabolites.
t½ is 3–5 hrs, and duration of action is 8–12 hrs (longer at higher
doses).
Sideeffects:
O ndanse tro n is g e ne rally we llto le rate d:
The only common side effect is headache and dizziness.
Mild constipation and abdominal discomfort occur in few
patients.
Hypotension, bradycardia, chest pain and allergic reactions
are reported, especially after i.v. injection.
NK1 RECEPTOR
ANTAGONISTS
Realizing that activation of Neurokinin (NK1) receptor in CTZ and
NTS by substance P released due to emetogenic chemotherapy and
other stimuli plays a role in the causation of vomiting,
Selective antagonists of this receptor have been produced, and are
being used as antiemetic.
Aprepitant
It is a recently introduced selective, high affinity NK1 receptor
antagonist that blocks the emetic action of substance P, with little
effect on 5 HT3 and D2 or other receptors.
Gastrointestinal motility is not affected.
Ondansetron + dexamethasone regimen significantly enhanced the
antiemetic efficacy against high emetogenic cisplatin based
chemotherapy.
ADJUVANT ANTIEMETICS
Corticosteroids (e.g. dexamethasone 8–20 mg i.v.)
More often employed to augment the efficacy of other primary
antiemetic drugs like metoclopramide and ondansetron against highly
emetogenic regimens.
Corticosteroids benefit both acute and delayed emesis. The Basis of
the effect appears to be their anti-inflammatory action.
Benzodiazepines
The weak antiemetic property of BZDs is primarily based on the
sedative action.
Used as adjuvant to metoclopramide/ondansetron,
diazepam/lorazepam (oral/ i.v.) help by relieving the psychogenic
component, anticipatory vomiting and produce amnesia for the
unpleasant procedure.
They also suppress dystonic side effects of metoclopramide
Cannabinoids:
The active principle of the hallucinogen Cannabis indica that
possesses antiemetic activity against moderately emetogenic
chemotherapy.
It probably acts through the CB1 subtype of cannabinoid receptors
located on neurones in the CTZ and/ or the vomiting centre itself.
Dronabinol
Produced synthetically or extracted from Cannabis. it can be used
as an alternative antiemetic for moderately emetogenic
chemotherapy in patients.
The CNS actions limit the use of dronabinol to few nonresponsive
patients. Its antiemetic action can be supplemented by
dexamethasone.
DIGESTANTS
These are substances intended to promote digestion
of food.
A number of proteolytic, amylolytic and lipolytic
enzymes are marketed in combination formulations.
Vigorously promoted for dyspeptic symptoms, and as
appetite stimulants or health tonics.
They are occasionally beneficial, only when
elaboration of enzymes in g.i.t. is deficient.
Their routine use in tonics and appetite improving
mixtures is irrational.
1. PepsinMaybeusedalongwithHCl ingastric achyliadue to atrophic
gastritis, gastric carcinoma, pernicious anaemia, etc.
2. PapainIt is aproteolytic enzymeobtainedfromraw papaya. Its
efficacy after oral ingestion is doubtful.
3. Pancreatin:
It is amixtureof pancreatic enzymes obtained from hog and pig
pancreas. It contains amylase, trypsin and lipase, and is indicated in
chronic pancreatitis or other exocrine pancreatic deficiency states.
Fat and nitrogen content of stools may be reduced and
diarrhoea/steatorrhoea may be prevented.
It has to be used as enteric coated tablets or capsules to protect the
enzymes from being themselves digested in stomach by pepsin.
4. DiastaseandTakadiastaseTheseareamylolytic enzymes
obtained from the fungus Aspe rg illus o ryz ae . The y have been used in
pancreatic insufficiency.
5. Methyl polysiloxane (Dimethyl polysiloxane, Simethicone,
Dimethicone)
It is a silicone polymer—reduces surface tension and collapses froth,
‘antifoaming agent’.
It is not absorbed from g.i.t. and is pharmacologically inert.
Added to antacid, digestant and antireflux preparations, it is briskly
promoted as a remedy for ‘gas’, a very common gastric complaint.
It is also claimed to coat and protect ulcer surface, to aid dispersion of
antacids in gastric contents, and to prevent gastroesophageal reflux.

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Emetics and Anti emetics

  • 2. Nausea and vomiting are thought to be protective reflexes that serves to rid the gastrointestinal tract of toxic substances They are symptoms of altered functions but are not diseases Nausea denotes the feeling of impending vomiting, whereas vomiting refers to the forceful expulsion of contents of stomach and upper intestinal tract through the mouth Retching is the labored rhythmic respiratory activity which usually precedes vomiting
  • 3. MECHANISM OF VOMITING Controlled by vomiting centre in the medulla Stimuli are relayed to this centre from peripheral areas. i.e gastric mucosa and other parts of GIT. Sensory stimuli also arise within the central nervous system itself i.e cerebral cortex and vestibular apparatus and the impulses are transmitted to the vomiting centre The lack of BBB at the chemoreceptor trigger zone (CTZ) (so what )
  • 4. Nausea and vomiting may be the symptoms of pregnancy or infections, drugs, radiation, painful stimuli, metabolic and emotional disturbance or due to travel sickness The main neurotransmitter involved in the control of vomiting are acetylcholine , histamine, 5-hydroxytryptamine and dopamine
  • 5. EMETICS The drugs that produce vomiting are called as emetics MUSTARD and COMMON SALT act peripherally by irritating the stomach and are used as household emetics MORPHINE and APOMORPHINE are centrally acting emetics, they induce by stimulating CTZ. IPECAC is a safe emetic. It has both central and peripheral actions.
  • 6. Emetics are contraindicated in certain cases of poisoning. Contraindication for the use of emetics are Children Comatose patients Corrosive and caustic poisoning CNS stimulant drug poisonin Kerosene poisoning Morphine and phenothiazine poisoning
  • 7. ANTIEMETICS(CLASSIFICATION ) Classification: Anticholinergics :Hyoscine, Dicyclomine H1antihistaminics: Pro m e thazine , Diphenhydramine, Dimenhydrinate, Doxylamine, Meclozine (Meclizine), Cinnarizine. Neuroleptics: Chlorpromazine, (D2 blo cke rs) Triflupromazine, Prochlorperazine, Haloperidol, etc. Prokinetic drugs: Me to clo pram ide , Domperidone, Cisapride, Mosapride, Itopride 5-HT3 antagonists: O ndanse tro n, Granisetron, Palonosetron, Ramosetron NK1receptorantagonists: Aprepitant, Fosaprepitant Adjuvant antiemetics: Dexamethasone, Benzodiazepines, Dronabinol, Nabilone
  • 9. ANTICHOLINERGICS Scopolamine is the drug of choice used to prevent motion sickness. It blocks the afferent impulses to the vomiting centre by its anticholinergic action. Its sedative effect also contributes to its antiemetics effect Scopolamine is not effective for other types of vomiting Adverse effects: Sedation, Dryness of mouth Blurred vision Urinary retention
  • 10. ANTIHISTAMINES (H1- BLOCKERS) H1 blockers are mainly useful for the prevention of motion sickness. They are also effective in morning sickness. Postoperative and other types of vomiting Dimenhydrinate, diphenhydramine, promethazine, cysclizine and meclizine are some H1 blockers These drug are having antihistaminergic, anti cholinergic, weak antidopaminergic and sedative properties1 Antiemetics effect is due to sedative and central anticholinergic
  • 11. Cyclizine and meclizine have less sedative effect and among the antihistamine Cyclizine has the shortest duration of action (8 hours) and Meclizine has longest duration of action (24 hours) Meclizine is used for sea sickness Doxylamine is promoted in India for morning sickness Cinnarizine is used as antivertigo drug Uses: Motion sickness, morning sickness, drug induced, postoperative, radiation sickness, cancer chemotherapy induced vomiting
  • 12. NEUROLEPTICS The older neuroleptics (phenothiazines, haloperidol) are potent antiemetics; act by blocking D2 receptors in the CTZ. Antagonize apomorphine induced vomiting and have additional antimuscarinic as well as H1antihistaminic property. They have broad spectrum antiemetic action effective in: Drug induced and postoperative nausea and vomiting (PONV). Disease induced vomiting: gastroenteritis, liver disease, migraine Malignancy associated and cancer chemotherapy (mildly emetogenic) induced vomiting. Radiation sickness vomiting (less effective). Morning sickness: should not be used except in hyperemesis gravidarum.
  • 13. Neuroleptics are less effective in motion sickness: the vestibular pathway does not involve dopaminergic link. Acute muscle dystonia may occur after a single dose, especially in children and girls. The antiemetic dose is generally much lower than antipsychotic doses. These agents should not be administered until the cause of vomiting has been diagnosed; otherwise specific treatment of conditions like intestinal obstruction, appendicitis, etc. may be delayed due to
  • 14. Prochlorperazine This D2 blo cking phe no thiazine is a labyrinthine suppressant, has selective antivertigo and antiemetic actions. It is highly effective when given by injection in vertigo associated vomiting, and to some extent in CINV. Prochlorperazine is used as an antiemetic, but not as antipsychotic. Muscle dystonia and other extrapyramidal side effects are the
  • 15. PROKINETIC DRUGS These are drugs which promote gastrointestinal transit and speed gastric emptying by enhancing coordinated propulsive motility. This excludes traditional cholinomimetics and anti-ChEs which produce tonic and largely uncoordinated contraction. Metoclopramide Metoclopramide, a substituted benzamide, is chemically related to procainamide, but has no pharmacological similarity with it. Introduced in early 1970s as a ‘gastric hurrying’ agent, it is a commonly used antiemetic.
  • 16. Actions: GIT: Me to clo pram ide has m o re pro m ine nt e ffe ct on upper g.i.t.; increases gastric peristalsis while relaxing the pylorus and the first part of duodenum → speeds gastric emptying This action is independent of vagal innervation, but is stronger when vagus is intact. Lower esophageal sphincter (LES) tone is increased and gastroesophageal reflux is opposed. It also increases intestinal peristalsis to some extent, but has no significant action on colonic motility and gastric secretion.
  • 17. CNS Me to clo pram ide is an e ffe ctive antie m e tic; acting on the CTZ, blocks apomorphine induced vomiting. The gastrokinetic action may contribute to the antiemetic effect. However, it has no chlorpromazine (CPZ) like antipsychotic property, though it does share the extrapyramidal and prolactin secretion augmenting action of CPZ.
  • 18. MECHANISM OF ACTION: Metoclopramide acts through both dopaminergic and serotonergic receptors 1. D2antagonism: Do pam ine (acting thro ug h D2 receptors) is an inhibitory transmitter in the g.i.t Normally acts to delay gastric emptying when food is present in stomach. It also appears to cause gastric dilatation and LES relaxation attending nausea and vomiting. Metoclopramide blocks D2 receptors and has an opposite effect— hastening gastric emptying and enhancing LES tone by augmenting ACh release.
  • 19. 2. 5-HT4agonism Me to clo pram ide acts in the g.i.t. to enhance ACh release from myenteric motor neurones. The g astric hurrying and LES to nic e ffe cts are mainly due to this action which is synergized by bethanechol and attenuated by atropine. 3. 5-HT3antagonism At hig h co nce ntratio ns metoclopramide can block 5-HT3 receptors present on inhibitory myenteric interneurones and in NTS/ CTZ. The peripheral action can augment Ach release in the gut, but appears to be minor. The central anti 5-HT3 action appears to be significant only when large doses are used to control CINV.
  • 20. Adverse effects Sedation, dizziness, loose stools, muscle dystonias (especially in children). Long-term use can cause parkinsonism, galactorrhoea and gynaecomastia, No harmful effects are known when used during pregnancy. Though the amount secreted in milk is small, but suckling infant may develop loose motions, dystonia, myoclonus.
  • 21. Uses: Antiemetic: Metoclopramide is an effective and popular drug for many types of vomiting— postoperative, drug induced, disease associated (especially migraine), radiation sickness, etc, but is less effective in motion sickness. Gastrokinetic: (a) When emergency general anaesthesia has to be given and the patient has taken food less than 4 hours before. (b) To relieve postvagotomy or diabetic gastroparesis associated gastric stasis. (c) To facilitate duodenal intubation Dyspepsia: and other functional g.i.t disorders. Metoclopramide may succeed in stopping persistent hiccups Gastointestinal reflux disease: Metoclopramide may benefit milder cases of GERD, but is much less effective than PPIs/H2 blockers. It does not aid healing of esophagitis, but may be used as adjuvant to acid suppressive therapy
  • 22. DOMPERIDONE It is a D2 receptor antagonist, chemically related to haloperidol, but pharmacologically related to metoclopramide. Unlike metoclopramide, its prokinetic action is not attenuated by atropine and is based only on D2 receptor blockade in upper g.i.t. Domperidone crosses blood-brain barrier poorly. Accordingly, extrapyramidal Side effects are rare, but hyperprolactinaemia can occur. The antiemetic action is exerted mainly through CTZ which is not protected by blood-brain barrier.
  • 23. CISAPRIDE This benzamide derivative is a prokinetic with little antiemetic property, because it lacks D2 receptor antagonism. Effects of cisapride on gastric motility resemble metoclopramide, i.e. gastric emptying is accelerated, LES tone is improved and esophageal peristalsis is augmented The prokinetic action is exerted mainly through 5-HT4 agonism which promotes ACh release from myenteric neurones, aided by weak 5-HT3 antagonism which suppresses inhibitory transmission in myenteric plexus. Enteric neuronal activation via 5-HT4 re ce pto r also pro m o te s cAMP- dependent Cl secretion in the colon, increasing water content of stools. Safety of cisapride was challenged by reports of serious ventricular arrhythmias and death, mainly among patient
  • 24. 5-HT3 ANTAGONIST Ondansetron Developed to control cancer chemotherapy/radiotherapy induced vomiting, and later found to be highly effective in PONV and disease/drug associated vomiting as well. It blocks the depolarizing action of 5-HT exerted through 5-HT3 receptors on vagal afferents in the g.i.t. as well as in NTS and CTZ. Cytotoxic drugs/radiation produce nausea and vomiting by causing cellulardamage release of mediators including 5-HT fromintestinal→ mucosa activation of vagal afferents in the gut emetogenic→ → impulses to the NTS and CTZ. Ondansetron blocks emetogenic impulses both at their peripheral origin And their central relay. It does not block dopamine receptors.
  • 25. Pharmacokinetics: O ral bio availability o f o ndanse tro n is 60–70% due to first pass metabolism. It is hydroxylated by CYP1A2, 2D6 and 3A, followed by glucuronide and sulfate conjugation. No clinically significant drug interactions have been noted. It is eliminated in urine and faeces, mostly as metabolites. t½ is 3–5 hrs, and duration of action is 8–12 hrs (longer at higher doses).
  • 26. Sideeffects: O ndanse tro n is g e ne rally we llto le rate d: The only common side effect is headache and dizziness. Mild constipation and abdominal discomfort occur in few patients. Hypotension, bradycardia, chest pain and allergic reactions are reported, especially after i.v. injection.
  • 27. NK1 RECEPTOR ANTAGONISTS Realizing that activation of Neurokinin (NK1) receptor in CTZ and NTS by substance P released due to emetogenic chemotherapy and other stimuli plays a role in the causation of vomiting, Selective antagonists of this receptor have been produced, and are being used as antiemetic. Aprepitant It is a recently introduced selective, high affinity NK1 receptor antagonist that blocks the emetic action of substance P, with little effect on 5 HT3 and D2 or other receptors. Gastrointestinal motility is not affected. Ondansetron + dexamethasone regimen significantly enhanced the antiemetic efficacy against high emetogenic cisplatin based chemotherapy.
  • 28. ADJUVANT ANTIEMETICS Corticosteroids (e.g. dexamethasone 8–20 mg i.v.) More often employed to augment the efficacy of other primary antiemetic drugs like metoclopramide and ondansetron against highly emetogenic regimens. Corticosteroids benefit both acute and delayed emesis. The Basis of the effect appears to be their anti-inflammatory action. Benzodiazepines The weak antiemetic property of BZDs is primarily based on the sedative action. Used as adjuvant to metoclopramide/ondansetron, diazepam/lorazepam (oral/ i.v.) help by relieving the psychogenic component, anticipatory vomiting and produce amnesia for the unpleasant procedure. They also suppress dystonic side effects of metoclopramide
  • 29. Cannabinoids: The active principle of the hallucinogen Cannabis indica that possesses antiemetic activity against moderately emetogenic chemotherapy. It probably acts through the CB1 subtype of cannabinoid receptors located on neurones in the CTZ and/ or the vomiting centre itself. Dronabinol Produced synthetically or extracted from Cannabis. it can be used as an alternative antiemetic for moderately emetogenic chemotherapy in patients. The CNS actions limit the use of dronabinol to few nonresponsive patients. Its antiemetic action can be supplemented by dexamethasone.
  • 30. DIGESTANTS These are substances intended to promote digestion of food. A number of proteolytic, amylolytic and lipolytic enzymes are marketed in combination formulations. Vigorously promoted for dyspeptic symptoms, and as appetite stimulants or health tonics. They are occasionally beneficial, only when elaboration of enzymes in g.i.t. is deficient. Their routine use in tonics and appetite improving mixtures is irrational.
  • 31. 1. PepsinMaybeusedalongwithHCl ingastric achyliadue to atrophic gastritis, gastric carcinoma, pernicious anaemia, etc. 2. PapainIt is aproteolytic enzymeobtainedfromraw papaya. Its efficacy after oral ingestion is doubtful. 3. Pancreatin: It is amixtureof pancreatic enzymes obtained from hog and pig pancreas. It contains amylase, trypsin and lipase, and is indicated in chronic pancreatitis or other exocrine pancreatic deficiency states. Fat and nitrogen content of stools may be reduced and diarrhoea/steatorrhoea may be prevented. It has to be used as enteric coated tablets or capsules to protect the enzymes from being themselves digested in stomach by pepsin.
  • 32. 4. DiastaseandTakadiastaseTheseareamylolytic enzymes obtained from the fungus Aspe rg illus o ryz ae . The y have been used in pancreatic insufficiency. 5. Methyl polysiloxane (Dimethyl polysiloxane, Simethicone, Dimethicone) It is a silicone polymer—reduces surface tension and collapses froth, ‘antifoaming agent’. It is not absorbed from g.i.t. and is pharmacologically inert. Added to antacid, digestant and antireflux preparations, it is briskly promoted as a remedy for ‘gas’, a very common gastric complaint. It is also claimed to coat and protect ulcer surface, to aid dispersion of antacids in gastric contents, and to prevent gastroesophageal reflux.