drugs acting on git
DESCRIPTION
Gastrointestinal agents' chemistry & synthesisTRANSCRIPT
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Presented by,
ROSHNI ANN BABY
Pharm. Chemistry
M.Pharm Part I
*Drugs Acting on Gastro
Intestinal Tract
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*CONTENTS
INTRODUCTION TO GI AGENTS
EMETICS
ANTIEMETICS
DIARRHOEA AND ANTIDIARRHOEALS
CONSTIPATION AND LAXATIVES
MISCELLANEOUS DRUGS
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*GASTRO INTESTINAL AGENTS
Drugs acting on gastrointestinal tract gastrointestinal
agents/drugs.
Classified as –
Drugs for peptic ulcer – Cimetidine, ranitidine, omeprazole,
misoprostol, sucralfate etc.
Emetics and anti emetics.
Laxatives – lactulose, bisacodyl, liquid paraffin, castor oil etc.
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Anti diarrhoeal drugs – Ispaghula, atropine, codeine,
loperamide, sulfasalazine etc.
Miscellaneous – Peppermint, cardamom, pepsin, papain,
ursodiol, chenodiol etc
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*EMETICS
Emetics drugs used to evoke vomiting.
Vomiting undesirable substances are ingested.
At emergency powdered mustard suspension or strong salt
solution may be used.
CLASSIFICATION.
Act on Chemoreceptor Trigger Zone(CTZ).
eg: Apomorphine.
Act reflexly and on CTZ.
eg: Cephaeline.
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*APOMORPHINE.
Mechanism of action(MOA)
Acts centrally by stimulating the
medullary CTZ connected with
vomiting centre
Uses
As emetic.
OHOH
N
CH3
H
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*CEPHAELINE
MOA.
Locally by irritating the gastric mucosa & centrally by
stimulating the medullary CTZ to induce
vomiting.
Uses – as emetic.
Chemically it is an alkaloid found in ipecac.
CH3
H
H
CH3
CH3
O
O
N
NH
OH
O CH3
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*ANTIEMETICS
Anti emetics drugs used to prevent or suppress
vomiting.
CLASSIFICATION OF ANTI EMETICS
Anticholinergics
eg: Hyoscine,Dicyclomine.
H1 antihistamines.
eg: Promethazine, Diphenhydramine, Dimenhydrinate,
Doxylamine, Cyclizine, Meclizine, Cinnarizine.
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Neuroleptics or D2 blockers.
eg: Chlorpromazine, Prochlorperazine, Haloperidol.
Prokinetic drugs.
eg: Metoclopramide, Domperidone, Cisapride, Mosapride,
Tegaserod.
5HT3 antagonists.
eg: Ondansetron, Granisetron.
Adjuant antiemetics.
eg: Dexamethasone, Benzodiazepine, Cannabinoids.
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*ANTICHOLINERGICS
HYOSCINE
MOA
Blocks conduction of
nerve impulses across a
cholinergic link in the pathway
leading from the vestibular
apparatus to the vomiting centre.
Uses
For motion sickness.
O
O
O
N OH
CH3
9-methyl-3-oxa-9-azatri
cyclo[3.3.1.02,4]non-7-yl
(2S)-3-hydroxy-2-phenylpropanoate
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*DICYCLOMINE
MOA
Same as that of hyoscine.
2-(diethyl amino)ethyl(bicyclohexane)-
1- carboxylate.
Uses
As antiemetic, spasmolytic, in motion sickness, morning
sickness.
O
O N
CH3
CH3
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*H1 ANTIHISTAMINES.
MOA OF ANTIHISTAMINES
Act by both relaxing the smooth muscles and also act
centrally to depress vomiting centres.
They diminish vestibular stimulation & depress labyrinthine
function.
H1 antagonism.
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*PROMETHAZINE
Uses
Antihistaminic
Antiemetic
sedative
10-(2-(dimethylamino)propyl)
phenothiazine.
CH3
S
N
CH3
N
CH3
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S
NH
PHENOTHAIZINE
S
N
NaNH2ClCH2CHN(CH3)2
S
N
CH3
N
CH3
CH3
+
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*DIPHENHYDRAMINE
Uses
Antihistaminic
Antiemetic
Antitussive
2-(diphenylmethoxy)
Sedative N,N-dimethylethanamine.
CH3
O
N
CH3
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*MECLIZINE
Uses
Antihistaminic
Antiemetic
1-(p-chlorophenylbenzyl)-4-
(m-methylbenzyl)piperazine.
Cl
NN
CH3
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*CYCLIZINE
1-(diphenylmethyl)-4-methyl piperazine.
Uses
In postoperative and drug induced vomiting.
In motion sickness.
C
H
C6H5
N N CH3
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*
NH NH + CH3COCl N NHCH3
O
CH3I
-HIN N CH3
CH3
O
HCl
NH N CH3+
Cl
N N CH3-HCl
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*NEUROLEPTICS
MOA – They block D2 receptors in the CTZ.
CHLORPROMAZINE.Uses
Antipsychotic
Antiemetic
Antitussive
2-chloro-10-(3-(dimethylamino)
propyl)phenothiazine.
CH3
CH3N
N
S
Cl
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*HALOPERIDOL
4-(4-(p-chlorophenyl)-4-hydroxy
piperidone)-4-N-fluorobutyrophenone
Uses
Antipsychotic
antiemetic
CCH 2CH2CH2
O
F N
Cl
OH
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*PROCHLORPERAZINE
2-chloro-10-[3-(4-methyl-1-piperazinyl) propyl ] phenothiazine
Uses
antiemetic
S
N Cl
(CH2)3 N N CH3
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*
S
NH
Cl
2 CHLORO PHENOTHAIZINE
+ N NCH3 Cl-HCl
NaNH2/TOLUENE
NNCH3
S
N Cl
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*PROKINETIC DRUGS
METOCLOPRAMIDEMOA
D2 antagonism,
5HT3 antagonism,
5HT4 agonism in CTZ
or NTS.
Uses
Antiemetic 4-amino-5-chloro-N-(2-(diethyl-
aminoethyl)-2-methoxy benzamide
NH2
Cl
O
NHN
CH3
CH3
O
CH3
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*DOMPERIDONE
5-chloro-1-(1-(3-(2-oxo2,3-dihydro-1H-benzo
imidazol-1-yl)propyl)piperidin-4-yl)-1H-benzo
imidazol-2(3H)-one.
MOA – D2 antagonism in CTZ.
Uses
Antiemetic
ONH
N
O
N
N
NH
Cl
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*5HT3 ANTAGONISTS
ONDANSETRONAct via CTZ or NTS
Uses
In chemotherapy induced vomiting.
In post operative vomiting.
CH3O
N
N N
CH3
9-methyl-3-[(2-methyl-1H-imidazol-1-yl)methyl]-1,2,3,9-tetrahydro-4H-carbazol-4-one
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*GRANISETRON
Has long half life compared to
ondansetron.
Uses
In chemotherapy induced vomiting
In post operative vomiting
O
N
CH3
NH
N
N
CH3
1-methyl-N-(9-methyl-9-azabicyclo[3.3.1]non-3-yl)-1H-indazole-3-carboxamide
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DIARRHOEA
Loose bowel movements resulting into the frequent
passage of watery,uniformed stools with or without
mucous and blood.
Classification
Osmotic diarrhoea
Something in the bowel draws water from the body into the
bowel.
Eg;Sorbitol is not absorbed by the body but draws water from
the body into the bowel, resulting in diarrhoea.
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Secretory diarrhoea
Occurs when the body is releasing water into the bowel,
many infections, drugs causes secretory diarrhoea.
Exudative diarrhoea
Diarrhoea with the presence of blood and pus in the stool.
This occurs with inflammatory bowels disease (IBD), such as
Crohn’s disease or ulcerative colitis etc.
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Acute diarrhoea
Sudden onset in a previously healthy person
Lasts from 3 days to 2 weeks
Self-limiting
Resolves without sequels
Chronic diarrhoea
Lasts for more than 3 weeks.
Associated with recurring passage of diarrhoeal stools, fever,
loss of appetite, nausea, vomiting, weight loss, and chronic
weakness
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CAUSES OF DIARRHOEA
Acute Diarrhoea
Microbes
Drug induced
Nutritional
Chronic Diarrhoea
Tumours
Diabetes
Addison’s disease
Hyperthyroidism
Irritable bowel syndrome
E. Coli bacteria Rotavirus
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DRUG THERAPY
i. Specific antimicrobial drugs
ii. Non specific antidiarrhoeal drugs
ORAL REHYDRATION
THERAPY
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Specific anti microbial drugs
A. Antimicrobials are of no value
Due to non infective causes such as
Irritable bowel syndrome
Colic disease
Pancreatic enzyme deficiency etc
Rota virus causes acute diarrhoea, specially in children
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B. Antimicrobials are regularly useful
choleraTetracyclines,
chloramphenicoletc
Clostridium difficile
Vancomycin, metronidazole etc
amoebiasisMetronidazole,
dioxonidfuroate
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NON SPECIFIC ANTIDIARROEALS
1.Adsorbents
Eg; kaolin, pectin, calcium carbonate. Etc
2.Anti secretory drugs
Eg; sulphasalazine, bismuth sub salicylate,
atropine etc.
3.Antimotility drugs
Eg: codeine, loperamide, diphenoxylate etc
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Functions of Antidiarrhoeal Drugs
Decrease irritation to the intestinal wall
Block GI muscle activity to decrease movement
Affect CNS activity that cause GI spasm and stop
movement
Relief of symptoms and compensation of fluid &
electrolyte loss
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Non Specific Antidiarrhoeal Drugs
Adsorbents
Coat the walls of the GI tract
Bind to the causative bacteria or toxin, which is then
eliminated through the stool
Examples: bismuth subsalicylate, kaolin-pectin, activated
charcoal.
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Side Effects
Increased bleeding time
Constipation, dark stools
Confusion
Hearing loss, metallic taste, blue gums
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Anti secretory drugs
Agents which reduce the secretion
Decrease intestinal muscle tone and peristalsis of GI tract
Result: slowing the movement of faecal matter through the
GI tract
Examples: belladonna alkaloids, atropine, sulphasalazine,
hyoscyamine
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Side effects
Urinary retention, impotence
Headache, dizziness, confusion, anxiety, drowsiness
Dry skin, rash, flushing
Blurred vision, photophobia, increased intraocular
pressure
Hypotension, hypertension, bradycardia, tachycardia
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Antimotility drugs
Decrease bowel motility and relieve rectal spasms
Decrease transit time through the bowel, allowing more
time for water and electrolytes to be absorbed
Examples: codeine, loperamide, diphenoxylate
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Side effects
Drowsiness, sedation, dizziness, lethargy
Nausea, vomiting, anorexia, constipation
Respiratory depression
Bradycardia, palpitations, hypotension
Urinary retention
Flushing, rash, urticaria
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O
N
N
C CH2
CH2C
C
O
CH2
CH3
Diphenoxylate HCl
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CH2
CH3
NHO
O
+ OCH2
CH2
CH2
CH3
NO
O
CH2
CH2OH
CH2
CH3
NO
O
CH2
CH2Cl
CCH3H +
N
N
C CH2
CH2 O
O
CH2
CH3
C
ethyl 4-phenylpiperidine-4-carboxylate ethyl 1-(2-hydroxyethyl)-4-phenylpiperidine-4-carboxylate
ethylene oxide
SYNTHESIS OF DIPHENOXYLATE HCL
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N
N
C CH2
CH2
OH
C
Cl
O
CH3CH3
LOPERAMIDE
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N
NH
OS
N
N
OH
O
OH
O
SULPHASALAZINE
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O
OH
OH
NH2
Cl
N O
OH
OH
N
+
H
S
O
O
N N
NH2
H
N
N
O
S
N
N
OH
O
OH
O
5-amino-2-hydroxybenzoic acid
NaNO2/HCl
5-[(Z)-chlorodiazenyl]-2-hydroxybenzoic acid
4-amino-N-(pyridin-2-yl)benzenesulfonamide
2-hydroxy-5-{(E)-[4-(pyridin-2-ylsulfamoyl)phenyl]diazenyl}benzoic acid
Synthesis of Sulphasalazine
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Metabolism of Sulphasalazine
Sulphasalazine[H]
Gut
NH2
OH
O
OH
5- Amino salicylic acid
+
HO
SN
NO
N-(pyridin-2-yl)benzenesulfonamide
Prodrug, having low solubility and poorly absorbed from
ileum.
The azo bond split by colon bacteria into Sulfapyridine and
5-amino salicylic acid.
Blocks cyclooxgenase and lipooxygenase pathway and
reduce mucosal secretion.
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Laxatives
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CONSTIPATION
Constipation is the infrequent and/or unsatisfactory
defecation fewer than 3 times per week.
Abnormally infrequent and difficult passage of faeces through
the lower GI tract
Symptom, not a disease
Disorder of movement through the colon and/or rectum
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CAUSES OF CONSTIPATION
Diet
Lack of exercise
Irregular bowel habits
Drug induced
Disease States/Conditions
Spasm of colon
Dysfunction of myenteric plexus
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SYMPTOMS OF CONSTIPATION
Infrequent defecation
Nausea
Vomiting
Anorexia
Feeling full quickly
Stools that are small, hard, and/or difficult
to evacuate
Rectal bleeding
Weight loss (in chronic constipation)
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• Mild action, elimination of soft stools but formed stools.
Laxative or aperients
• Stronger action resulting in more fluid evacuation.
Purgative or cathartic
LAXATIVES
Drugs that promote evacuation of bowels.
Based on intensity of action
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Classification
• Methyl cellulose, ispaghula,Agar, Psyllium seeds
1. Bulk forming
• Liquid paraffin, Glycerine, Olive oil
2. Stool softener
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Diphenylmethanes
• Bisacodyl, phenolphthalein, sodium
picosulphate.
Anthraquinones
• Senna, cascara sagrada
5HT4 agonist • Tegaserod
Fixed oil • Castor oil
3. Stimulant purgative
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4. Osmotic purgativeMagnesium salts, lactulose
etc
Bulk Forming Laxatives
Improve stool consistency and frequency with regular use
Ensure good fluid intake to prevent faecal impaction
Onset of action 2-3 days
Side Effects may include bloating, flatulence, distension
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Stool Softeners
May be useful with anal fissures of haemorrhoids
Liquid paraffin is not recommended for treatment of
constipation
- risk of aspiration and lipoid pneumonia
- long term use may result in depletion of Vitamins
A, D, E and K
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Stimulant Laxatives
Increase intestinal motility by stimulating colonic nerves
Useful with opioids
Onset of action 8-12 hours
May develop tolerance
2nd line therapy in elderly due to risk of electrolyte
disturbances
Cramping, diarrhoea, dehydration
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Osmotic Laxatives
Increase fecal water content
Result: bowel distention, increased peristalsis, and
evacuation
Improving stool frequency
Onset of action – up to 48 hours
Metabolized by bacteria flatulence
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OO
N
OOCH3 CH3
Bisacodyl
ON
CH + 2C6H5OH
H2SO
4
(CH3CO)
2O
N
O
O
C
CH3
C
CH3
O
O
pyridine-2-carbaldehyde
(pyridin-2-ylmethanediyl)dibenzene-3,1-diyl diacetate
Synthesis of Bisacodyl
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O
O
OH
OH
O
O
O
+
OH
OH
H2SO
4
O
O
OH
OH
phathalic anhydride
phenol
phenolphthalein
3,3-bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one
Synthesis of phenolphthalein
Phenolphthalein
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Na Na
N
OOSS
O-
O-
O
O O
O
sodium picosulphate
-{(pyridin-2-ylmethanediyl)dibenzene-4,1-diyl bis[hydrogenato(2-)-O sulfate]}disodate(2-)
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OH
NHN NH
NH
CH3Tegaserod
3-[(E)-{2-[(pentylamino)methyl]hydrazinylidene}methyl]-1H-indol-5-ol
It is 5HT4 agonist used for the management of
irritable bowel syndrome and constipation
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*Contract stomach muscles and stimulate hunger
N
N
3-phenyl-3,4-dihydroquinazoline( Orexin)
Bitters – secretion of gastric juice
Eg: Quassins
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*
*Disturbance of appestat – weight regulating
mechanism in hypothalamus
Eg: Dextro amphetamine
CH3
NH2
CH3
NH2
CH3
Aptrol
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**HCl
*Pepsin
O
O
CH3
O
CH3
O
OH
CH3
Florantyrone
Si O
CH3
O
CH3
Si CH3
CH3
CH3
Si
CH3
CH3
CH3
n
Simethicone
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*
*Protect sensitive surface from irritation
*Lozenges or gargles
*Cohesive substances like colloids, dextrins, sugar, starches
*Eg: Acacia
Tragacanth
Liquorice
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*
*PPI
*H2 blockers
*Sodium alginate
*Prokinetic drugs
*Antacids
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*
*Expulsion of gases
*Eg: Sodium bicarbonate
Peppermint oil
Tincture of cardamom
Oil of dill
Tincture of ginger
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*
*Anticholinergics
O O CH3
CH3
NH
N
CH3
CH3
Camylofin
NH
O
CH3
O
CH3
OCH3
OCH3
Dicycloverine
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Liver protectants*Chenodiol ( chenodeoxy cholic acid)
*Ursodiol ( Ursodeoxy cholic acid)
Gall stone dissolving drugs *Metadoxine
*L-Ornithine
*L- Aspartase
*Silymarin
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*
Proton pump inhibitor
IL – YANG pharmaceuticals
NH
NH
N
S
O
N
CH3 O CH3
Ilaprazole
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Anti diarroheal
HIV Assosiated
NAPO pharmaceuticals
O
O
OHOH
OH
OHOH
OH
OH
OH
OH
OH
O
OH
OH
OH
OH
OH
Crofelimer
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Antiemetic drug
Neurokinin receptor antagonist
N
N
N
F
CH3
O
CH3
N
O
CH3
CH3
CF 3
CF 3
Casopirant
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REFERENCE
1.Text Book of Medicinal Chemistry by V. Alagarsamy,
1st edition volume-II, page no:1137
2.Bently and Driver’s Text book of Pharmaceutical Chemistry
8th edition, page No. 724, 625.
3.Essentials of Medicinal Pharmacology by K D TRIPATHI,
6th edition page No. 651
4.Clinical Pharmacy and Therapeutics, by Roger Walker,
Cate Whitelsia, 4th edition, Page No: 824- 832
5. Foye’s principles of Medicinal Chemistry, 5th edition,
page No: 474-475
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