2. Emetics
emetics are drugs that produce or induce emesis/vomiting.
MECHANISM OF EMESIS/VOMITING
emesis is the forceful expulsion of the contents of the stomach via
the mouth or sometimes through the nose.
the vomiting reflex is stimulated by two centers in the medulla
vomiting center
chemoreceptor trigger zone(CTZ)
3. Haw CTZ is stimulated?
tactile stimulation of the back of the throat, a reflex to get
rid of something that is too big or too irritating to be
swallowed.
excessive stomach distention.
Increase intercranial pressure by direct stimulation
Stimulation of the vestibular receptor in the inner ear
intense pain fiber stimulation
direct stimulation by varies chemicals, including fumes,
certain drugs, and debris from cellular death
4. Classification of emetics
1. STIMULANTS OF CTZ
A. apomorphine
B. morphine
2. IRRITANTS OF GASTRIC MUCOSA
A. Mustard
B. sodium chloride
3. BOTH CTZ STIMULANT AND IRRITANT EFFECT
A. ipecacuanha
B. digitalis
5. APOMORPHINE
given through subcutaneously or through intramuscular -6mg
causes vomiting within 15 min
in hypertensive individual, however ,even a subtherapeutic dose may
elicit sever emesis and collapse
vomiting is often accompanied by sedation
it should not be used if respiration is depressed
larger doses often produce restlessness, tremor, occasionally
convulsion
sometimes may cause hypotension, syncope and coma
6. MUSTARD
it is household remedy to induce vomiting
volatile oil
dose-1teaspoonful with water
formed as a result of a reaction between a glycoside and an enzyme in the
presence of water
SODIUM CHLORIDE:
given orally
Withdraw fluids from the cells lining the stomach thus causes irritation
which reflex emesis.
7. Ipecacuanha(Emetine)
act by irritating gastric mucosa as well as through CTZ
dried root of cephalis ipecacuanha contains emetine
commonly available as syrup to induce emesis at a dose of:
adults-15-20ml
children- 10-15ml
infant-5ml
takes 15 min or more for the effect.
12. prokinetics
these drugs which promote gastrointestinal motility and quicken
gastric emptying
drug available:
metochlorpramide
domperidone
mechanism of action of prokinetic drug
D2 antagonist
5-HT4 agonism
5HT3 antagonism
13. metoclopramide
introduced in early 1970s as a “gastric hurrying agent”
widely used antiemetic
it has both central and peripheral effect:
central-block the dopaminergic receptor
peripheral- increased gastric emptying at a dose of-5-
10mg
14. Interaction:
hastens absorption of many drugs:
Aspirin
diazepam etc. facilitate the gastric emptying
reduced absorption of digoxin
adverse effect:
sedations, dizziness, diarrhea, muscle dystonia
long term use can cause parkinsonism, galactorrhea and
gynecomastia
15. domperidone
D2 antagonist
chemically related to haloperidol but pharmacologically related to
metoclopramide
has lower ceiling antiemetic and prokinetic action
poorly crosses BBB
rare extra pyramidal side effect
given with lavodo or bromocriptine to counteract their dose limiting
emetic action
absorbed orally, but bioavailability is only 15% due to first pass
metabolism
16. completely metabolized and excreted in urine
t1/2 I 7.5hr
side effect are less than with metoclopramide:
dry mouth
loose stool
headache
rashes
galactorrhea
cardiac arrhythmias on rapid I.V injection
17. ANTIMUSCARINIC
competitively inhibit action of acetylcholine at muscarinic receptor
hyoscine:
most effective in controlling motion sickness
0.2-0.4 mg oral, I.M
brief duration of action
transdermal patch 1.5mg applied behind thee pinna to be delivered
over 3 days-suppresses motion sickness while producing only mild
side effect
18. Neuroleptics
they act by suppressing the CTZ so they antagonize vomiting
produced by drug which stimulate CTZ.
act by block d1 receptors in the CTZ
antiemetic dose is much lower than antipsychotic doses
these agents should not be administered until the cause of vomiting
has been diagnosed
19. broad spectrum antiemetic, effective in:
drug induced and post anesthetic nausea and vomiting
disease induced vomiting
chemotherapy induced
morning sickness: should not be used except in
hyperemesis gravidarum
20. 5-HT3 Antagonists
(5-HT3) receptor antagonists block the vomiting reflex by inhibiting
5-HT3 receptors in the vomiting center, the chemoreceptor trigger
zone and in the small intestine.
high first pass metabolism
Excreted by the liver and kidney
given once or twice daily-orally or intravenously.
even though 5 HT3 receptors are present in vomiting center and CTZ,
the antiemetic action is restricted to emesis caused by vagal
stimulation.
21. Granicetron
it is 10 to 15 times more potent than ondansetron
more effective in chemotherapy
dose- iv 1mg
Ondansetron(emeset):
block 5 HT3 receptors in GIT and CTZ
specially used in the chemotherapy,
dose- 4mg in each ampule, 4,8 mg tablet
22. Antihistamine
they act by sedating the vomiting center
they are safer for long term use
effective in motion sickness and vomiting due to labyrinthine
disorder
all antimotion drugs are more effective when taken ½-1 hr. before
commencing journey
once sickness has started, it is more difficult to control