Drugs Affecting
Gastrointestinal Function
OUTLINE
 Peptic Ulcer
 Digestion
 Vomiting
 Diarrhea
 Bile
 Review-Questions
Ulcer-Background
 Epidemiology
 incidence of a disease: 10%-12%
 DU > GU (3:1)
 Etiology
 General consideration: No Acid No Ulcer
 Main Destroy Factors: ①HCl, ②Pepsin, ③Hp
 Protective Barrier: Mucus-HCO3 Physiology
 HCl: P-cell, H2, M1, G-R, H+-pump
Anti-ulcer Targets
 HCl
 Mucus
 Hp
Anti-ulcer Classification
Antacids--- Neutralize HCl
Gastric Antisecretory Drugs
HCl secretion
I.
II.
1.
2.
Antagonize Rs. on Parietal Cell--- H2,M3,
G
Inhibitor of H+-Pump
III. Protectors of Mucosa
IV. Agents kill HP
Ⅰ. Antacids
 Mechanism:
 Alkalizers——To Neutralize HCl
 Agents:
 Mg(OH)2 Al(OH)3 CaCO3
NaHCO3
 Adverse Effect:
 Systemic alkalosis, Diarrhea , CO2
Major constituents of antacids
Neutralizing
Constituent
Capacity
NaHCO3
CaCO3
Al(OH)3
Mg(OH)2
High
Moderate
High
High
Salt
Formed in
Stomach
Solubility
of Salt
NaCl
High
CaCl2
AlCl3
MgCl2
Adverse Effects
Systemic alkalosis, fluid
retention
Hypercalcemia,
Moderate nephrolithiasis, milk-alkali
syndrome
Low
Constipation,
hypophosphatemia; drug
adsorption reduces bioavailability
Low
Diarrhea, hypermagnesemia
(in patients with renal
insufficiency)
Ⅱ.1.⑴ H2-R Antagonists
 Mechanism:
 Pharmacologic Effects:
 Basal gastric acid
nocturnal secretion
 Agents:
 Cimetidine， Ranitidine， Famotidine
 Adverse Effect:
 Gynecomastia, prolactin , CYP450
headache
,
Ⅱ.1.⑵ Antimuscarinic Agents
 Mechanism:
 Blocking M3-R on Parietal Cell, M-R on ECL
cell and G cell
 Pharmacologic Effects:
 HCl
spasmolysis
 Agents:
 Atropine ，Probanthine
 Pirenzepine - M1,M2-R selection
 Adverse Effect:
Ⅱ.1.⑶ Antagonist of G-R
 Mechanism:
 Competing Gastrin-R on Parietal Cell
 Pharmacologic Effects:
 HCl
Mucosal
 Agents:
 Proglumide
 Adverse Effect:
Ⅱ.2. Proton Pump Inhibitors
 Mechanism:
 H+,K+-ATPase
H+
 Pharmacologic Effects:
 HCl
& Hp
 Agents:
 Omeprazole（losec）
 Lansoprazole
 Pantoprazole，Rabeprazole
 Adverse Effect:
K+
Ⅲ. Mucosal Protective Agents
1. Derivatives of Prostaglandin:
Misoprostol (PGE1), Enprostil
 Mechanism:
 HCl ; Pepsin
 Mucus-HCO3- ;
 Cytoprotective effect
 Pharmacologic Effects:
 Prevention of ulcers iduced by NSAIDs
 Contraindication：
 Women with childbearing
2. Sucralfate
 Mechanism:
Polymerization & gelatine barrier
PGE2
Mucus-HCO3Hp
 Pharmacologic Effects:
Effective in Duodenal Ulcers
 Notice:
Acid pH
Empty stomach
3. CBS

Mechanism:
Pepsin
PGE1
Mucus-HCO3Coating
Hp
（disputed）
4. Teprenone
5. Marzulene
Ⅳ. Anti-Hp Drugs
 90% DU,70% GU --- Helicobacter pylori
(G-)
1. Anti-Ulcer Agents:
①
Bismuth Compounds
② Proton Pump Inhibitors
③ sucralfate
2. Antibacterial Drugs:
①
Amoxicillin
② Gentamicin
③ Metronidazole
Combination Therapy
 Therapy of triad
 Oversea
PPI + two Antibacterial Drugs
 Domestic
CBS + PPI or H2-R Antagonist +
Antibacterial Drug
Digestion Aids
1. Contents of Digestive Juice:
 Pepsin
 Pancreatin
2. Helpful Bacterias in Bowel:
 biofermin
Antiemetic Drugs and Drugs
Promoting Gastrointestinal Motility
 Nausea and Vomiting mechanism:
CTZ
Chemical
stimuli
5-HT, D2, M1, H1
Other
areas
Chemoreceptor
trigger zone
Vestibular
apparatus
Vomiting
Stomach and
Abdomminal
Musculature
Vomiting
Center
1. Antagonists of Receptors of
① H1: Nucleus of tractus solitarius, vestibulocerebellar
pathway——Diphenhydramine, Dimenhydrinate
② M : Nucleus of tractus solitarius, CTZ——
Scopolamine
③ D2 : CTZ, Nucleus of tractus solitarius, Stomach,
Small intestine——Thiethylperazine，Metoclopramide
④ 5-HT3 : Stomach, Small intestine, CTZ, Nucleus of
tractus solitarius——Ondansetron，Granisetron
2. Prokinetics：
 Metoclopramide
Blocking Gastrointestinal
 Domperidone
D2-R
 Cisapride：Ach release↑
Antidiarrheal Drugs and
Adsorbents
Opium preparation and Derivatives
1.
Opiate receptors in Gastrointestinal tract →
tone↑motility↓（μ），secretion↓（δ），Ach release ↓
Loperamide： Derivatives of Haloperidol


2.
Astringents
①
Tannalbin
② Bismuth subsalicylate, Bismuth subcarbonate
3.
Adsorbants
①
Medicinal Charcoal
② Kaolin
Laxatives
1.
Contact cathartics


2.
Osmotic laxatives


3.
Irritant or stimulant → intestinal motility↑
Phenolphthalein, Rhubarb, Senna, Castor oil
nonabsorbable → distending → peristalsis
MgSO4, Na2SO4, Lactulose, Celluloses
Surface-active agents


Lubricating, Stool soften
Liquid paraffin
Choleretic drug
1. Cholic Acid
HMG-CoA reductase (rate limiting enzyme)↓
→ bile salt↑，cholesterol ↑
 Chenodiol (Chenodeoxycholic acid)

2. MgSO4

cholecystokinin ↑
3. Cinametic acid
4. Anethol trithione
Review-Questions
 The classification of drugs used in the
treatment of peptic ulceration.
 the mechanisms and the agents of each.