A Brief Look at the Gastrointestinal System - Pharmacology

The gastrointestinal (GI) system consists of the alimentary canal and the digestive tract that begins with the oral cavity and extends to the anus. The major structures of the GI system are the oral cavity (mouth, tongue, and pharynx),esophagus, stomach, small intestine (duodenum, jejunum, and ileum), large intestine (cecum, colon, rectum), and the anus.

In addition to these major structures, the GI system has several accessory organs and glands that include the salivary glands, pancreas, gallbladder, and liver.

Food that enters the oral cavity is broken down into small pieces in the mouth. Starches are then digested by amylase found in saliva. Small pieces of food are voluntarily moved to the back of the mouth and moved down to the esophagus in a process commonly referred to as swallowing. When the food reaches the esophagus, it is moved to the stomach and intestines with an involuntary movement called peristalsis.

The esophagus is a tube connecting the oral cavity to the stomach and is lined with mucous membranes that secrete mucus. The esophagus has two sphincters. These are the superior (hyperpharyngeal) sphincter and the lower sphincter that prevents gastric juices from entering the esophagus (gastric reflux).

The stomach is a hollow organ that holds between 1000 to 2000 mL of contents that takes about 2-3 hours to empty. It, too, has two sphincters. These are the cardiac sphincter (located at the opening of the esophagus), and the pyloric sphincter (that connects the stomach to the head of the duodenum).

The stomach has mucosal folds containing glands that secrete gastric juices used to break down food (digest) into its chemical elements. Lipid-soluble drugs and alcohol are absorbed in the stomach. There are four types of cells in the stomach. These are:

Chief Cells

Chief cells secrete proenzyme pepsinogen (pepsin).

Parietal Cells

Parietal cells secrete hydrochloric acid (HCl)

Gastrin-Producing Cells

Gastrin-producing cells secrete gastrin, which is a hormone that regulates the release of enzymes during digestion.

Mucus-Producing Cells

Mucus-producing cells release mucus that protect the stomach lining from the gastric juices.

The small intestine extends from the ileocecal valve at the stomach to the duodenum. The cecum is attached to the duodenum, which is the site where most medication is absorbed. Most foods are also absorbed in the small intestine.

The duodenum releases secretin, which is a hormone that suppresses gastric acid secretion. This results in the intestinal juices having a higher pH than the gastric juices in the stomach. The hormone cholecystokinin is also released. It simulates the flow of bile into the duodenum. Hormones, bile, and pancreatic enzymes trypsin, chymotrypsin, lipase, and amylase digest carbohydrates, protein, and fat in preparation for absorption in the small intestine.

The small intestine lead into the large intestine where undigested material from the small intestine is collected. The large intestine also absorbs water and secretes mucus while moving the undigested material using peristaltic contractionsto the rectum where it is eliminated through defecation.

VOMITING

Vomiting (emesis) is the expulsion of gastric contents of the stomach through the esophagus and out the oral cavity. Vomiting is sometimes preceded by nausea, which is a queasy sensation, although vomiting can occur without nausea. Vomiting can occur for a number of reasons. These include motion sickness, viral and bacterial infections, food intolerance, surgery, pregnancy, pain, shock, effects of selected drugs, radiation, and disturbances of the middle ear affecting equilibrium.

Vomiting occurs when two major centers in the cerebrum are stimulated. These are the chemoreceptor trigger zone (CTZ) that lies near the medulla and the vomiting center in the medulla. The CTZ receives impulses from drugs, toxins, and the vestibular center in the ear. These impulses are transmitted by the neurotransmitter dopamine to the vomiting center. The neurotransmitter acetylcholine is also a vomiting stimulant. Sensory impulses such as odor, smell, taste, and gastric mucosal irritation are transmitted directly to the vomiting center.

When the vomiting center is stimulated, motor neurons respond causing contraction of the diaphragm, the anterior abdominal muscles, and the stomach. The glottis closes, the abdominal wall moves upward, and the stomach contents are forced up the esophagus.

When vomiting occurs, try to identify the cause before treating the patient. Begin treatment with non pharmacological measures such as drinking weak tea, flattened carbonated beverages, gelatin, Gatorade, and for children, Pedialyte. Crackers and dry toast may also be helpful.

Nausea and vomiting that occur during the first trimester of pregnancy should be treated with non pharmacologic remedies since amtimetics can cause possible harm to the fetus. If dehydration occurs because vomiting is severe, intravenous fluids may be needed to restore body fluid balance.

If non pharmacological measures fail, then administer antiemetic medication. There are two groups of antiemetics: nonprescription and prescription. Nonprescription antiemetics are purchased over-the-counter and used to prevent motion sickness. They have little effect controlling severe vomiting. They must be taken 30 minutes before traveling and are not effective once vomiting occurs.

Antihistamine antiemetics such as diphenhydrinate (Dramamine), meclizine hydrochloride (Antivert), and diphenhydramine hydrochloride (Benadryl) are over-the-counter medications that prevent nausea, vomiting, and dizziness (vertigo) caused by motion by inhibiting stimulation in the middle ear. They also cause drowsiness, dryness of the mouth, and constipation.

Several over-the-counter drugs such as bismuth subsalicylate (Pepto-Bismol) act directly on the gastric mucosa to suppress vomiting. Such drugs can be taken for gastric discomfort or diarrhea. Do not give Pepto-Bismol to children who are vomiting who might be at risk for Reyes syndrome as it contains salicylates.

Phosphoratedcarbodydrate solution (Emetrol), a hyperosmolar carbohydrate is also available over-the-counter. It decreases nausea and vomiting by changing the gastric pH or by decreasing smooth muscle contractions of the stomach. This drug has a high sugar content and should not be used by diabetics.

Prescription antiemetics act as antagonists to dopamine, histamine, serotonin, and acetylcholine. Antihistamines and anticholinergics act on the vomiting center and decrease stimulation of the CTZ and vestibular pathways.

There are eight classifications of prescription antiemetics.

ANTIEMETICS

Antihistamines

Antihistamines are used to decrease nausea and vomiting that occur after surgery. They are also used for the management of motion sickness and to treat allergic symptoms. Examples are Vistaril, Atarax, and Phenergan.

Anticholinergics

Anticholinergics are used to prevent and treat nausea, vomiting and motion sickness. They are also used to treat vertigo that is associated with vestibular system disease. Scopolamine is an example of an anticholinergic agent.

Dopamine antagonists

Dopamine antagonists suppress emesis by blocking dopamine receptors in the CTZ. These include phenothiazines, butyrophenones, and metoclopramide. Common side effects are extrapyramidal symptoms (EPS) caused by blocking the dopamine receptors and hypotention. Phenothiazines are the largest group of antiemetics. They are also used for anxiety (see Chapter (Nervous System Drugs) ). Dopamine antagonists suppress emesis by blocking dopamine receptors. They act by inhibiting the CTZ. Not all phenothiazines are effective antiemetics. The dose is generally smaller when phenothiainerase is used as an antiemetic. Promethazine (Phenergan) is a phenothiazine. It was introduced as an antihistamine with sedative side effects and can be used for motion sickness.

Phenothiazines and the miscellaneous antiemetics such as benzquinamide, diphenidol, metclopramide, and trimethobenzamide act on the CTZ center. Chlorpromazine (Thorazine) and prochlorperazineedisylate (Compazine) are tranquilizers used for both psychosis and vomiting.

Butyrophenones include haloperidol (Haldol) and droperidol (Inapsine). They block dopamine2 receptors in the CTZ. Extrapyramidal side effects (EPS) are likely to occur if these drugs are used over an extended period of time. Hypotension can also occur.

Metoclopramide (Reglan) suppresses emesis by blocking the dopamine and serotonin receptors in the CTZ. High doses can cause sedation and diarrhea. The occurrence of EPS is more prevalent in children than adults.

Benzodiazepines

Benzodiazepines indirectly control nausea and vomiting. Lorazepam (Ativan) is the choice drug in this category and may be given with metoclopramide.

Serotonin antagonists

Serotonin antagonists suppress nausea and vomiting by blocking the serotonin receptors in the CTZ and the afferent vagal nerve terminals in the upper GI tract. Two serotonin antagonistsondanestron (Zofran) and granisetron (Kytril) are effective in suppressing chemotherapy-induced emesis. They do not block the dopamine receptors. Therefore, they do not cause EPS. Zofran is commonly used to prevent and treat post-operative nausea and vomiting.

Glucocorticoids

Glucocorticoids (corticosteroids) include Dexamethasone (Decadron) and methylprednisolone (Solu-Medrol). They are administered intravenously for short-term use. This reduces the side effects caused by using glucocorticoids. (See Chapter (Inflammation) for a discussion on the use of steroids.)

Cannabinoids (for cancer patients)

The cannabinoids act on the cerebral cortex and have the same side effects and adverse reactions as antihistamines and anticholinergic. These include drowsiness, dry mouth, blurred vision, tachycardia, and constipation. Cannabinoids include dronabinol and nabilone. These drugs should not be administered to glaucoma patients because they dilate the pupils (mydriasis). They are contra-indicated for use in patients with psychiatric disorders and also used as an appetite stimulant for patients with AIDS. Side effects include mood changes, euphoria, drowsiness, dizziness, headaches, depersonalization, nightmares, confusion, incoordination, memory lapse, dry mouth, orthostatic hypotension, hyper-tension, and tachycardia. Less common symptoms include depression, anxiety, and manic psychosis.

MISCELLANEOUS

Miscellaneous antiemetics include benzquinamide hydrochloride (Emete-Con), diphenidol (Vontrol), and trimethobenzamide (Tigan). They do not act strictly as antihistamines, anticholinergics, or phenothiazides. They suppress the impulses to the CTZ. Diphenidol also prevents vertigo by inhibiting impulses to the vestibular area. Benzquinamide appears to have antiemetic, antihistaminic, and anticholinergic effects. It inhibits stimulation to the CTZ center and decreases activity in the vomiting center. It can also increase cardiac output and elevate blood pressure. Side effects and adverse reactions of the miscellaneous antiemeticsinclude drowsiness and anticholinergic symptoms such as dry mouth, increased heart rate, urine retention, constipation, and blurred vision. Benzquinamide should be used cautiously in clients with cardiac problems such as dysrhythmias. It can cause CNS stimulation, including nervousness, excitement, and insomnia. Trimethobenzamide can cause hypotension, diarrhea, and EPS.

EMETICS INDUCING VOMITING

When a patient ingests a toxic substance, it is critical that the toxin be expelled or neutralized before the body can absorb it. However, vomiting should not be induced if the toxin is a caustic substance such as ammonia, chlorine bleach, lye, toilet cleaners, or battery acid. Regurgitating these substances can cause additional injury to the esophagus. Vomiting should also be avoided if petroleum distillates are ingested. These include gasoline, kerosene, paint thinners, and lighter fluid.

In cases where vomiting is contraindicated, the patient should be administered activated charcoal, which is available in tablets, capsules, or suspension. Charcoal absorbs (detoxifies) ingested toxic substances, irritants, and intestinal gas. Activated charcoal can be given as a slurry (30 grams in at least 8 oz. of water) or 12.5-50 grams in aqueous or sorbitol suspension. It is usually given as a single dose.

In cases where vomiting is desired, use one of two ways to expel a toxin:

The nonpharmacological treatment is to induce vomiting by stimulating the gag reflex by placing a finger or a toothbrush in the back of the patient’s throat. Pharmacological treatment involves administering an emetic to induce vomiting. Ipecac is the most commonly used emetic. Ipecac, available over the counter, should be purchased as a syrupnot a fluid extract. The syrup induces vomiting by stimulating the CTZ in the medulla and acts directly on the gastric mucosa.

Ipecac should be taken with at least eight or more ounces of water or juice (do not use milk or carbonated beverages). If vomiting does not occur within 20 minutes, then the dose should be repeated. If vomiting cannot be induced, then administer activated charcoal. The absorption of ipecac is minimal. Protein-binding is unknown and the half life is short. Duration of action is only 20-25 minutes. Do not attempt to induce vomiting if the patient is not fully awake and alert.

ANTI-DIARRHEA

Diarrhea is defined as frequent liquid stools that can be caused by foods, fecal impaction, bacteria (Escherichia coli, Salmonella), virus (parvovirus, rotavirus), toxins, drug reaction, laxative abuse, malabsorption syndrome caused by lack of digestive enzymes, stress and anxiety, bowel tumor, and inflammatory bowel disease such as ulcerative colitis or Crohn’s disease.

Diarrhea can be mild (lasting one bowel movement) or severe (lasting several bowel movements). Intestinal fluids are rich in water, sodium, potassium, and bicarbonate, and diarrhea can cause minor or severe dehydration and electrolyte imbalances. The loss of bicarbonate places the patient at risk for developing metabolic acidosis. Severe diarrhea can be life threatening in young, elderly, and debilitated patients.

Diarrhea is a symptom of an underlying cause. Therefore, you must treat the underlying cause while treating the diarrhea. Diarrhea can be treated with a combination of medications and non pharmacological measures such as clear liquids and oral solutions Gatorade, Pedialyte, or Ricolyte and intravenous electrolyte solutions.

For example, traveler’s diarrhea also known as Montezuma’s Revenge is an acute condition usually caused by E. coli that last less than 2 days but it can become severe. A patient experiencing traveler’s diarrhea may be given fluoroquinolone antibiotics and loperamide (Immodium) to slow peristalsis and decrease the frequency of the stools. Fluoroquinolone treats the underlying cause of diarrhea and loperamide treats the diarrhea itself.

Anti-diarrhea medications decrease the hypermotility (increased peristalsis) that stimulates frequent bowel movements. Antidiarrheals should not be used for longer than 2 days and should not be used if a fever is present. Anti-diarrhea medication is available in four classifications.

Opiates

Opiates decrease intestinal motility thereby decreasing persistalsis. Constipation is a common side effect. Examples are tincture of opium, paregoric (camphorated opium tincture), and codeine. Opiates are frequently combined with other antidiar-rheal agents and can cause central nervous system (CNS) depression when taken with alcohol, sedatives, or tranquillizers. Duration of action is about 2 hours.

Opiate-Related Agents

Opiate-related agents are drugs that are synthetic compounds similar to opiates. These drugs include diphenoxylate (Lomotil) (50% atropine to discourage abuse; amount of atropine is subtherapeutic) and loperamide. Both are synthetic drugs that are chemically related to meperidine (Demerol). Loperamide causes less CNS depression than diphenoxylate and can be purchased over-the-counter. It protects against diarrhea longer than a similar dose of Lomotil, reduces fecal volume, and decreases intestinal fluid and electrolyte losses. These drugs can cause nausea, vomiting, drowsiness, and abdominal distention. Tachycardia, paralytic ileus, urinary retention, decreased secretions, and physical dependence can occur with prolonged use.

Absorbents

Adsorbents coat the wall of the GI tract and adsorb bacteria or toxins that are causing the diarrhea. Adsorbents include kaolin and pectin, which are combined in the over-the-counter drug Kaopectate, and other antidiarrheals. Pepto-Bismol is considered an adsorbent because it adsorbs bacterial toxins. Bismuth salts can also be used for gastric discomfort. Colestipol and cholestyramine (Questran) are prescription drugs that have been used to treat diarrhea.

Anti-Diarrhea Combinations

Anti-diarrhea combinations are miscellaneous antidiarrheals that include colistin sulfate, furazolidone, loperamide, lactobacillus, and octreotide acetate. You may know these brand names drugs to alleviate diarrhea: Lomotil (diphenoxylateHCl with atropine sulfate) and parepectolin (paregoric, kaolin, pectin, alcohol). Most contain a synthetic narcotic ingredient.

CONSTIPATION

Constipation is the accumulation of hard fecal material in the large intestine. It is a common occurrence for the elderly due to insufficient water intake and poor dietary habits. Other factors that cause constipation are fecal impaction, bowel obstruction, chronic laxative use, neurologic disorders such as paraplegia, a lack of exercise, and ignoring the urge to have a bowel movement. Drugs such as anticholinergics, narcotics, and certain antacids can also cause constipation.

Constipation can be treated non pharmacologically and pharmacologically. The non pharmacological approach is to include bulk (fiber) and water in the patient's diet and have the patient exercise and develop routine bowel habits. The normal number of bowel movements is between 1-3 per day to 1 to 3 per week. Normal bowel movements vary from person to person.

The pharmacological approach is to administer laxatives and cathartics to eliminate fecal matter. Laxatives promote a soft stool and cathartics promote a soft-to-watery stool with some cramping. Harsh cathartics that cause a watery stool with abdominal cramping are called purgatives. Frequency of the dose determines whether the drug acts as a laxative or a cathartic.

Laxatives should be avoided if there is any question that the patient has an intestinal obstruction, severe abdominal pain, or symptoms of appendicitis, ulcerative colitis, or diverticulitis. Most laxatives stimulate peristalsis. Laxative abuse from chronic use of laxatives is a common problem, especially with the elderly. Dependence can become a problem.

There are four types of laxatives.

Osmotics (saline)

Osmotic laxatives (hyperosmolar) are salts or saline products, lactulose, and glycerin. The saline products are composed of sodium or magnesium, and a small amount is systemically absorbed. They pull water into the colon and increase water in the feces to increase bulk, which stimulates peristalsis. Saline cathartics cause a semi formed-to-watery stool depending on dose. However, they are contraindicated for patients who have congestive heart failure.

Osmotic laxatives contain three types of electrolyte salts: sodium salts (sodium phosphate or phospho-soda, sodium biphosphate), magnesium salts (magnesium hydroxide (milk of magnesia), magnesium citrate, magnesium sulfate (Epsom salts), and potassium salts (potassium bitartrate, potassium phosphate). Serum electrolytes should be monitored to avoid electrolyte imbalance. Good renal function is needed to excrete any excess salts.

High doses of salt laxatives are used for bowel preparation for diagnostic and surgical procedures. Also used for bowel preparation is polyethylene glycol (PEG) with electrolytes, commonly referred to as Colyte or GoLYTELY. PEG is administered in amounts of 3 to 4 liters over 3 hours. Patients may be advised to keep GoLYTELY refrigerated to make it more palatable. PEG is an isotonic, non absorbable osmotic substance that contains sodium salts. Therefore, patients with renal impairment or cardiac disorder can use potassium chloride.

Lactulose, another saline laxative, is not absorbed and draws water into the intestines and promotes water and electrolyte retention. Lactulose decreases the serum ammonia level and is useful in liver diseases such as cirrhosis. Glycerin acts like lactulose by increasing water in the feces in the large intestine. The bulk that results from the increased water in the feces stimulates peristalsis and defecation. Patients who have diabetes mellitus should avoid lactulose because it contains glucose and fructose.

Adequate renal function is needed to excrete excess magnesium. Patients who have renal insufficiency should avoid magnesium salts. Hypermagnesemia can result from continuous use of magnesium salts, causing symptoms such as drowsiness, weakness, paralysis, complete heart block, hypotension, flushing, and respiratory depression. Side effects from excess use are flatulence, diarrhea, abdominal cramps, nausea, and vomiting.

Stimulants (contact or irritants)

Stimulant laxatives increase peristalsis by irritating sensory nerve endings in the intestinal mucosa. Stimulant laxatives include those containing phenolphthalein (Ex-Lax, Feen-A-Mint, Correctol), bisacodyl (Dulcolax), cascara sagrada, senna(Senokot), and castor oil (purgative). Bisacodyl and phenolphthalein are two of the most frequently used and abused laxatives because they can be purchased over-the-counter.

Results occur in 6 to 12 hours. Stimulant laxatives such as bisacodyl are used to empty the bowel before diagnostic tests (for example, barium enema) because they are minimally absorbed from the GI tract. Most are excreted in feces. However, a small amount of bisacodyl absorption excreted in the urine changes the color to reddish-brown. With excessive use, fluid and electrolyte imbalances can occur (especially potassium and calcium). Mild cramping and diarrhea are side effects.

Caster oil is a harsh laxative (purgative) that acts on the small bowel and produces a watery stool within 2 to 6 hours. Therefore, this shouldn’t be taken at bedtime. Caster oil is used mainly for bowel preparation and seldom used to correct constipation. Caster oil should not be used in early pregnancy because it stimulates uterine contractions and spontaneous abortion can occur. Prolonged use of Caster oil can damage nerves resulting in loss of intestinal muscular tone.

Bulk-forming

Bulk-forming laxatives are natural fibrous substances that promote large, soft stools by absorbing water into the intestines and increasing fecal bulk and peristalsis. Bulk-forming laxatives are non-absorbable. Defecation usually occurs within 8 to 24 hours but can take up to 3 days after the start of therapy for the stool to become soft and formed.

Powdered bulk-forming laxatives come in flavored and sugar-free preparations and should be mixed in a glass of water or juice, stirred. The patient should drink it immediately, followed by a half to a full glass of water. Insufficient fluid intake can cause the drug to solidify in the GI tract, resulting in intestinal obstruction. Bulk-forming laxatives do not cause dependence and may be used by patients with diverticulosis, irritable bowel syndrome, ileostomy and colostomy.

Calcium polycarbophil (FiberCon), methylcellulose (Citrucel), fiber granules (Perdiem), and psyllium hydrophilic mucilloid (Metamucil) are examples of bulk-forming laxatives. Patients with hypercalcemia should avoid calcium polycarbophil because of the calcium in the drug. Metamucil is a nondigestible and nonabsorbent substance that when mixed with water, becomes a viscous solution. There is no protein-binding or half-life for the drug. It is excreted in the feces. There are no systemic effects. Nausea can occur with excessive use. The dry form can cause abdominal cramps.

Emollients

Emollients (surfactants) are stool softeners (surface-acting drugs) and lubricants used to prevent constipation and decrease straining during defecation by lowering surface tension and promoting water accumulation in the intestine and stool.

Emollients are frequently prescribed for patients after a myocardial infarction (heart attack) or surgery and are also given prior to administration of other laxatives in treating fecal impaction. Docusate calcium (Surfak), docusate potassium (Dialose), docusate sodium (Colace), and docusate sodium with casanthranol (Peri-Colace) are examples of stool softeners.

Lubricants such as mineral oil increase water retention in the stool. Mineral oil absorbs essential fat-soluble vitamins A, D, E, and K. Some of the minerals can be absorbed into the lymphatic system. Side effects include nausea, vomiting, diarrhea, and abdominal cramping. They are not indicated for children, the elderly, or patients with debilitating conditions because they can aspirate the mineral oil, resulting in lipid pneumonia.

Emollients are contraindicated in patients with inflammatory disorders of the GI tract, such as appendicitis, ulcerative colitis, undiagnosed severe pain that could be due to an inflammation of the intestines (diverticulitis, appendicitis), pregnancy, spastic colon, or bowel obstruction.

PEPTIC ULCER

A peptic ulcer is a sore or hole in the lining of the stomach or duodenum and is a term used to describe a lesion in the esophagus, stomach, or duodenum. More specific names are used to describe an ulcer located at a specific site. Duodenal ulcers (the first part of the small intestine) are more common than other types of peptic ulcers. Peptic ulcers are caused by hypersecretion of hydrochloric acid and pepsin that erode the GI mucosal lining.

Anyone can get an ulcer. Most ulcers are caused by an infection with the bacterium Helicobacter pylori not spicy food, acid, or stress and can be cured with antibiotics in about two weeks. The most common ulcer symptom is burning pain in the stomach: 1/2–11/2 hours after eating with gastric ulcers; 2-3 hours for a duodenal ulcer.

Gastric secretions in the stomach maintain a pH between 2 and 5. Pepsin, a digestive enzyme, activates at pH 2 and the acid-pepsin complex of gastricsecretions cause mucosal damage. If gastric secretions increase to pH 5, pepsin declines. The gastric mucosal barrier (GMB) is a thick, viscous, mucous lining and is a defense against corrosive substances. The two sphincter muscles cardiac and pyloric act as barriers to prevent reflux of acid into the esophagus and the duodenum. Esophageal ulcers result from reflux of acidic gastric secretion into the esophagus as a result of a defective or incompetent cardiac sphincter.

Gastric ulcers frequently occur because of a breakdown of the GMB.

Duodenal ulcers are caused by hypersecretion of acid from the stomach that passes to the duodenum because of

  • insufficient buffers to neutralize the gastric acid in the stomach.
  • a defective or incompetent pyloric sphincter.
  • hypermotility of the stomach.

Treatment of peptic ulcers is given in two-drug, three-drug, and four-drug regimens, or a combination medication consisting of multiple drugs combined into one package.

However, the American College of Gastroenterology no longer recommends two-drug regimens since they are not as effective as other treatment regimens. The different classes of medication that may be combined are listed below.

GASTROESOPHAGEAL REFLUX DISEASE (GERD)

Gastroesophageal reflux disease is an inflammation of the esophageal mucosa caused by reflux of stomach contents into the esophagus. GERD is caused by a malfunction of the esophageal sphincter brought about by smoking and obesity.

GERD is treated using common anti-ulcer drugs that neutralize the gastric contents and reduce gastric acid secretion. Once the content is neutralized, the esophageal mucosa has time to healfreeing the patient of symptoms of GERD.

There are eight groups of anti-ulcer drugs used to treat GERD. These are:

Tranquilizers

Tranquilizers have minimal effect preventing and treating ulcers. However, they reduce vagal stimulation and decrease anxiety. Librax is a commonly prescribed tranquilizer to treat GERD. Librax is a combination of the anxiolytic chlor-diazepoxide (Librium) and the anticholineraticclidinium (Quarzan) and is used in the treatment of ulcers.

Anticholinergic

Anticholinergics (antimuscarinics, parasympatholytics) relieve pain by decreas¬ing GI motility and secretion and by inhibiting acetylcholine and blocking his¬tamine and hydrochloric acid. Anticholinergics delay gastric emptying time and are used frequently to treat duodenal ulcers.

Anticholinergics should be taken before meals to decrease the acid secretion that occurs with eating. They should not be taken with antacids because antacids can slow the absorption of antichloinergic administration. Side effects include dry mouth, decreased secretions, tachycardia, urinary retention, and constipation. However, because gastric emptying time is delayed, gastric secretions can be stimulated and actually aggravate the ulceration.

Antacids

Antacids promote ulcer healing by neutralizing hydrochloric acid and reducing pepsin activity. Antacids don't coat the ulcer. There are two types of antacids: Those that have a systemic effect and antacids without a systemic effect. A systemic effect occurs when the antacid is absorbed.

Sodium bicarbonate is a systemic antacid that has many side effects including sodium excess that causes hypernatremia and water retention. Sodium bicarbonate also causes metabolic alkalosis related to the excess bicarbonate. Therefore, sodium bicarbonate is seldom used to treat peptic ulcers.

Calcium carbonate is most effective in neutralizing acid, however one third to one half of the drug can be systemically absorbed resulting in acid rebound. Hypercalcemia and “milk-alkali syndrome” can result from excessive use of calcium carbonate. Calcium carbonate is intensified if taken with milk products.

Nonsystemic antacids are composed of alkaline salts such as aluminum (aluminum hydroxide, aluminum carbonate) and magnesium (magnesium hydroxide, magnesium carbonate, magnesium trisilicate, and magnesium phosphate). A small degree of systemic absorption occurs with these drugs mainly with aluminum.

Magnesium hydroxide has greater neutralizing power than aluminum hydroxide, however magnesium compounds can be constipating in long-term use. A combination of magnesium and aluminum salts neutralizes gastric acid without causing constipation or severe diarrhea. Simethicone (an anti-gas agent) is found in many antacids.

Histamine2 (H2 blockers)

Histamine2 blockers prevent acid reflux in the esophagus by blocking the H2 receptors of the parietal cells in the stomach. This results in a reduction ofgastric acid secretion and concentration. Histamine2 blockers also cause headaches, dizziness, constipation, pruritus, skin rash, gynecomastia, decreased libido, and impotence. Examples include Cimetidene (Tagamet) Famotidene (Pepsid) Ranitidine (Zantac).

Proton pump inhibitors

Proton pump inhibitors (gastric acid secretion inhibitors, gastric acid pump inhibitors) inhibit gastric acid secretion 90% greater than the H2 blockers because they block the final step of acid production. Both omeprazole (Prilosec) and lansoprazole (Prevacid) are proton pump inhibitors used for the treatment of peptic ulcers and GERD. Those with hepatic impairment should take these drugs with caution and have liver enzymes monitored regularly.

Pepsin inhibitor

Pepsin inhibitors such as sucralfate (Carafate) are mucosal protective drugs that are non-absorbable and combine with protein to form a viscous substance that covers the ulcer. This protects it from acid and pepsin. Pepsin inhibitors do not neutralize acid or decrease acid secretions.

Prostaglandin E1 analogue

Prostaglandin analogue antiulcer drugs such as misoprostol (Cytotec), prevents and treats peptic ulcers by suppressing gastric acid secretion and increasing cytoprotective mucus in the GI tract. Prostaglandin analogue also moderately decreases pepsin secretion. Prostaglandin analogue is ideal for patients who have gastric distress from taking NSAIDS such as aspirin or indomethacin. Prostaglandin analogue should not be taken during pregnancy and by any women of childbearing age.

Gastrointestinal stimulants

Gastrointestinal stimulants are used to treat nocturnal heartburn caused by GERD and primarily prescribed for patients who do not respond to other drugs or non-drug therapy. Gastrointestinal stimulants increase gastric emptying time preventing acid reflux into the esophagus. Gastrointestinal stimulants also enhance the release of acetylcholine at the mysenteric plexus. Cisapride (Propulsid) is an example of a gastrointestinal stimulant.

Gastrointestinal stimulants should not be used for patients who have cardiac dysrhythmias especially ventricular tachycardia, ventricular flutter, or fibrillation. Nor should it be used for patients with is chemic heart disease, congestive heart failure, uncorrected electrolyte disorders (hypokalemia, hypomagnesemia), and renal or respiratory failure. An EKG should be done before and during therapy.


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