gastrointestinal drugs
TRANSCRIPT
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Gastrointestinal Drugs
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Acid-Related Pathophysiology
The stomach secretes: Hydrochloric acid (HCl) :- digestion and also serves as a barrier to infection
Bicarbonate :- natural mechanism to prevent hyperacidity
Pepsinogen :- enzymatic precursor to pepsin, an enzyme that digests dietary proteins
Intrinsic factor:- glycoprotein that facilitates gastric absorption of vitamin B12
Mucus:- protects the stomach lining from both HCl and digestive enzymes
Prostaglandins (cytoprotective):- serve a variety of anti – inflammatory and protective functions
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Glands of the Stomach
Cardiac
Pyloric
Gastric*
* The cells of the gastric gland are the largest in number and of primary importance when discussing acid control
* gastric glands play the most significant role in acid-related disorders.
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Cells of the Gastric Gland
Parietal cells
Produce and secrete HCl
Primary site of action for many acid-controller drugs
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Hydrochloric Acid
Secreted by the parietal cells when stimulated by food
Maintains stomach at pH of 1 to 4
Secretion also stimulated by: Large fatty meals Excessive amounts of alcohol Emotional stress Caffeine and chocolate
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Chief cells
Secrete pepsinogen, a proenzyme
Pepsinogen becomes pepsin when activated by exposure to acid
Pepsin breaks down proteins (proteolytic)
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Mucoid cells
Mucus-secreting cells (surface epithelial cells)
Provide a protective mucous coat
Protect against self-digestion by HCl
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D- Cell :
Release somatostatin to inhibit HCL secretion.
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Acid-Related Diseases
Caused by imbalance of the three cells of the gastric gland and their secretions
Most common: hyperacidity
Patient report symptoms of overproduction of HCl by the parietal cells as indigestion, heartburn, acid stomach
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PUD: peptic ulcer disease GERD: gastroesophageal reflux disease Helicobacter pylori (H. pylori)
Bacteria found in GI tract of 90% of patients with duodenal ulcers, and 70% of those with gastric ulcers
Combination therapy is used most often to eradicate H. pylori
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Drugs for peptic ulcer
1. Reduction of gastric acid secretion :
A . H2 Antagonists:- Cimetidine ,Famotidine, Ranitidine ,Roxatidine
B. Proton pump inhibitor: - omeprazole, Lansoprazole, Pantoprazole, Rabeprazole, Esomeprazole
C. Anticholinergics : Pirenzepine, Atropine, Propantheline, Oxyphenonium
D. Prostaglandin analogue : Misoprostol
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2. Neutralization of gastric acid (Antacid)
A. Systemic : Sodium bicarbonate
B. Nonsystemic : Magnesium hydroxide, Mag. Trisilicate, Aluminium hydroxide gel, Calcium carbonate
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3. Ulcer protectives : Sucralfate, Colloidal bismuth subcitrate (CBS)
4. Anti – H. pylori drugs : Amoxicillin, Clarithromycin, Metronidazole, Tinidazole, tetracycline
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Types of Acid-Controlling Agents
Antacids (to treat dyspepsia).
H2 antagonists
Proton pump inhibitors
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Antacids
A. Systemic :
• Sodium bicarbonate.
( It has a rapid onset and short duration of action since it is highly soluble, and offers rapid relief of pain.)
B. Nonsystemic :
• Magnesium hydroxide, • Mag. Trisilicate,• Aluminium hydroxide,• Calcium carbonate.
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The rationale for the use of antacids in peptic ulcer disease lies in the assumption that buffering of H+ in the stomach permits healing.
The buffering agents in the various antacid preparations consist of combinations of ingredients that include sodium bicarbonate, calcium carbonate, magnesium hydroxide, and aluminum hydroxide.
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Antacids DO NOT prevent the over-production of acid
Antacids DO neutralize the acid once it’s in the stomach
Quick onset of relief but last for a short duration
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Antacids
Given orally 1-3 hrs after meals and bedtime
Single dose provides 120mEq neutralizing capacity--equivalent to one dose of an H2RA
Mg+2 based preparations increase motility Diarrhea
Al+3 based preparations relax smooth muscle Constipation
Carbonate-containing preparations release CO2 Belching, nausea, distension, and flatulence.
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Antacids: Drug Effects
Reduction of pain associated with acid-related disorders
Raising gastric pH 1 point (1.3 to 2.3) neutralizes 90% of the gastric acid
Reducing acidity reduces pain
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Aluminum Salts
Forms: carbonate, hydroxide
Have constipating effects
Often used with magnesium to counteract constipation
Examples Aluminum carbonate Hydroxide salt Combination products (aluminum and magnesium)
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Magnesium Salts
Forms: carbonate, hydroxide, oxide, trisilicate
Commonly cause diarrhea; usually used with other agents to counteract this effect
Dangerous when used with renal failure —the failing kidney cannot excrete extra magnesium, resulting in hypermagnesemia
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Examples Hydroxide salt: magnesium hydroxide (MO
M)
Carbonate salt
Combination products aluminum and magnesium
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Calcium Salts
Forms: many, but carbonate is most common
May cause constipation
Their use may result in kidney stones
Long duration of acid action may cause increased gastric acid secretion (hyperacidity rebound)
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Sodium Bicarbonate
Highly soluble
Buffers the acidic properties of HCl
Quick onset, but short duration
May cause metabolic alkalosis
Sodium content may cause problems in patients with HF, hypertension, or renal insufficiency (fluid retention)
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Antacids and Antiflatulents
Antiflatulents: used to relieve the painful symptoms associated with gas
Several agents are used to bind or alter intestinal gas and are often added to antacid combination products.
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Antiflatulents
Simethicone
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Antacids: Side Effects
Minimal, and depend on the compound used
Aluminum and calcium Constipation
Magnesium Diarrhea
Calcium carbonate Produces gas and belching; often combined with simethico
ne
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Antacids: Drug Interactions
Absorption of other drugs to antacids Reduces the ability of the other drug to be absorbe
d into the body
Chelation Produces insoluble complexes Result: reduced drug absorption
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Drugs less absorbed when taking antacids include:
Tetracycline, Antifungals Ciprofloxacin Propranolol Captopril
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Antacids can also potentiate (make stronger) the following drugs:
Valproic acid: Used to treat epilepsy, bipolar disease and migraines.
Quinidine: cardiac drug used to treat certain heart arrhythmias.
Levodopa: Anti-Parkinson’s drug.
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Most medications should be given 1 to 2 hours after giving an antacid
Antacids may cause premature dissolving of enteric-coated medications, resulting in stomach upset.
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Be sure that chewable tablets are chewed thoroughly, and liquid forms are shaken well before giving
Caffeine, alcohol, spices may aggravate the underlying GI condition
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To be continue…..