PHARMACOLOGY OF GASTROINTESTINAL SYSTEM
I. Physiology of the Upper Gastrointestinal Tract From a pharmacologic perspective, the most important region of the upper • GastroInstestinal GI tract are the buccal and sublingual sublingual areas of the mouth and the stomach The oral mucosa in the sublingual region is relatively permeable, and drugs are • rapidly absorbed. The buccal region is less permeable, and drug absorption is slower. The buccal • region, has less salivary flow and drugs can be retained longer, making it better suited for sustained release delivery system. II. Physiology of the Lower Gastrointestinal Tract The lower GI tract consist of the small and large intestine • Small intestine is the longest portion of the alimentary canal and is the primary • organ of absorption.(With its many folds and finger like projection of villi an d microvilli, the lining of each villus is composed of a single layer of epithelial cell and contains blood capillaries) The stomach secretes acid, enzyme and hormones that are essential to digestive physiology Chief cells secretes the enzyme pepsinogen, which is then activated to become • pepsin, which is the digestive enzyme that breakdown proteins form food. Parietal cells secrete gastric (Hydrochloric) acid in the stomach., which provides • strong acidic environment that promotes conversion of pep sinogen to pepsin, helps breakdown food and kills microbes that might have been digested. o Secrete intrinsic factors, which is essential for absorption of Vit B12. parietal cells are target target for classes of drugs that reduce acid secretion. Parietal cells receive messages from several sources, which tells them to increase or decrease acid production. The cells contain receptors for the hormone, gastrin, histamine, and neurotransmitter acetylcholine Which are the three principle physiologic stimuli that regulate acid secretion from proton pump or H+, K+,-ATPase, located on the surface of parietal cells. PEPTIC ULCER Is a lesion or erosion located on either the stomach(gastric) or small • intestine( duodenal) mucosa that is associated with with inflammation PROTON PUMP INHIBITOR Drug of choice in the therapy o f Peptic Ulcer disease • Mechanism of action: acts by blocking H+,K+, ATPase ATPase (an enzyme responsible • for secreting HCL in the stomach) Half life 1.5 hours • Excreted in the urine(80%) and feces (20%) •
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Proton Pump Inhibitor Drugs o OMEPRAZOLE (Prilosec) o ESOMEPRAZOLE (Nexium) LANZOPRAZOLE(Prevacid)- used for patient having swallowing o capsules, its capsule can be easily opened and its content mixed with food. Available as a PO disintegrating tablet (Prevacid Solutab) that is place under the tongue and disintegrates within 1 minute. PANTOPRAZOLE ( Protonix) o OMEPRAZOLE Route: PO o OTC, indicated to relieve Heart burn o Mechanism of Action: Reduces Acid Secretion in the stomach by binding o irreversibly to the the enzyme H+,K+, ATPase. It inhibits the final pathway involved in acid secretion and effectively inhibits the active proton pumps. o
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Nursing responsibility: Monitor for Vitamine B12 and Folic Acid malabsorption because an acid environment is necessary to complete absorption of the drug Patient education: Take this medication 30 minutes before meals, preferably before breakfast. Eat foods with beneficial bacteria, such as yogurt, or take Lactobacillus Acidophillus supplements to replace ”friendly” bacteria Do not crush, break, chew ch ew tablets or capsule. If taking LANSOPRAZOLE, the granules from th capsule can be sprinkled into soft food as a apple sauce. Afterwards, drink full water to ensure all medication is taken. Avoid smoking,alcohol because it causes acid production.
H2 blockers or H2-Receptor Antagonist H2- Blockers suppress gastric acid secretion • H2 receptors are located in the parietal cells in the stomach, promotes gastric acid • secretion when activated. ANTACIDS should not be taken at the same time time with H2 blockers because • absorption is diminish. H2 Blockers : • RANITIDINE(Zantac) o CIMETIDINE(Tagamet) o FAMOTIDINE( Pepcid) o o NIZATIDINE( Axid) RANITIDINE •
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Indicated for Gastric Ulcer, Duodenal ulcer, and GERD to promote healing and prevent recurrence. Route: PO, IM,IV Gastric ulcers heal more slowly than duodenal ulcer and thus require longer therapy. Duoudenal ulcer requires 6-8weeks and gastric ulcers requires 12 of therapy Adequate healing of ulcer 4-8 weeks Ranitidine blocks the H2 receptors on the parietal cells I the stomach to decrease acid production. Both daytime and nocturnal basal gastric acid secretion are suppressed Nursing Responsibility: Administer the IV form form of this medication slowly over several several minutes to prevent Bradycardia and hypotension due to the antagonism of histamine receptors located in the heart.IntraVenous preparation of H2 blockers are utilized for the prevention of stress ulcer seen in intensive care unit(ICU) setting in critical ILL PATIENTS Take drug with meals because the bufferng effect of food may increase the therapeutic effect
ANTACIDS Are alkaline substance that neutralize stomach ac id to treat symptoms of • heartburn. Provide temporary relief of heartburn • They relieve symptoms of antacid, but do not promote ulcer healing because • they do not protect or coat the stomach wall Antacids are inorganic compound that contain aluminum, magnesium, • sodium, or calcium that that neutralize gastric gastric acid and inactivates pepsin. ANTACID Drugs: • 1.ALUMINUM HYDORXIDE(Alterna GEL) • 2.SODIUM BCARBONATE ( Alka –Seltzer) • 3.MAGNESIUM HYDORXIDE and ALUMINUM HYDROXIDE with • sinethicon (Maalox) 4.MAGNESIUM HYDROXIDE (Milk of Magnesia) • 5.CALCIUM CARBONATE ( Tums) • •
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Nursing Intervention:: Assess for bowel changes: Magnesium based products may cause Diarrhea. • Calcium and Aluminum may cause constipation • Take antacids at least 2 hours before other PO medications, because drug absorption maybe affected. Take 1 antacid 1 hour before meal or 2 hours after meal.
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This drug may make stool appear white
Pharmacotherapy of Helicobacter Pylori Gram negative Helicobacter Pylori is approximately associated with 70% • of patient with peptic ulcer disease. Risk factors for H. pylori include residing in a developing country, • domestic crowding, unclean water H. Pylori is the only known organism that has been found to survive the • hostile condition in the stomach. H. Pylori adopts well to the acidic environment of the stomach. H. Pylori neutralizes the high acidity surrounding it and makes chemicals • called ADHESIN that allows the bacteria to penetrate the G.I mucosa which initiates inflammation. Increase gastrin secretion and decreased bicarbonate secretion play a role in ulcer formation. H. pylori produces large amount of UREASE, an enzyme that breaks • down urea to ammonia and carbon monoxide. Ammonia neutralizes the the acid around the H.Pylori to survive the acidic environment. However, the ammnonia is toxic to mucosal cell and erodes the mucosal layer of the stomach. H. pylori finds finds its home on the submucosal layer of stomach, producing larger damage. Regimen used to eradicate Helicobacter Pylori Pylori Initial Regimen: OMEPRAZOLE CLARITHROMYCIN, AMOXICILLIN. • Alternative Regimen:OMEPRAZOLE CLARITHROMYCIN, • METRONIDAZOLE Those with peptic ulcer who are not infected with H. pylori should not o receive antibiotics, because it has been found that this patient has a worsen outcome if they receive H. pylori treatment. o Test for H. pylori before initiating treatment
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