Gastrointestinal Agents Felix Hernandez, M.D.

Acid Reducing Agents Histamine Receptor Blockers: Histamine Receptor Blockers: MOA: Histamine receptor Antagonist MOA: Histamine receptor Antagonist Indications: duodenal/gastric ulcer, hypersecretion of acid, GERD Indications: duodenal/gastric ulcer, hypersecretion of acid, GERD Side Effects: Well tolerated. Diarrhea, decreased libido, impotence. Can be hepatotoxic and renal toxic Side Effects: Well tolerated. Diarrhea, decreased libido, impotence. Can be hepatotoxic and renal toxic Interactions: increases concentration of anticoagulants Interactions: increases concentration of anticoagulants Drugs: Drugs: Cimetidine (Tagamet) Cimetidine (Tagamet) Ranitidine (Zantac) Ranitidine (Zantac) Famotidine (Pepcid) Famotidine (Pepcid)

Acid Reducing Agents Antacids Antacids Aluminum Salts Aluminum Salts MOA: Neutralize gastric acid thus causing a reduction in mucosal irritation. Relief of pain precedes healing. MOA: Neutralize gastric acid thus causing a reduction in mucosal irritation. Relief of pain precedes healing. Indications: symptomatic relief of gastric acid irritation Indications: symptomatic relief of gastric acid irritation Side Effects: constipation, hypercalcemia, hypophosphatemia Side Effects: constipation, hypercalcemia, hypophosphatemia Notes: Magnesium antacids are co administered to prevent constipation Notes: Magnesium antacids are co administered to prevent constipation Calcium Carbonate Calcium Carbonate MOA: same MOA: same Indications: same Indications: same Side effects: constipation, hypercalcemia, metabolic alkalosis, milk-alkali syndrome (rare) Side effects: constipation, hypercalcemia, metabolic alkalosis, milk-alkali syndrome (rare) Magnesium Salts Magnesium Salts MOA: same MOA: same Indications: same Indications: same Side Effects: diarrhea, hypermagnesemia  N/V, hyporeflexia, decreased muscle tone Side Effects: diarrhea, hypermagnesemia  N/V, hyporeflexia, decreased muscle tone Sodium Citrate Sodium Citrate MOA: same MOA: same Indications: Pre-op antacid Indications: Pre-op antacid Side Effects: Horrible taste but is likely to cause aspiration pneumonitis because it is nonparticulate Side Effects: Horrible taste but is likely to cause aspiration pneumonitis because it is nonparticulate

Acid Reducing Agents Sucralfate (Carafate) Sucralfate (Carafate) MOA: Sucrose and polyaluminum hydroxide polymerize at low pH to form a protective coating MOA: Sucrose and polyaluminum hydroxide polymerize at low pH to form a protective coating Indications: Prophylaxis and treatment of duodenal ulcers Indications: Prophylaxis and treatment of duodenal ulcers Side Effects: Constipation Side Effects: Constipation Interferes with the absorption of fluroquinolone AB Interferes with the absorption of fluroquinolone AB

Proton Pump Inhibitors Drugs: Omeprazole (Prilosec), Lansoprazole (Prevacid), Esomeprazole (Nexium), Pantoprazole (Protonix) Drugs: Omeprazole (Prilosec), Lansoprazole (Prevacid), Esomeprazole (Nexium), Pantoprazole (Protonix) MOA: inhibits hydrogen/potassium ATPase (Proton pump) of the parietal cells thus reducing acid secretion. MOA: inhibits hydrogen/potassium ATPase (Proton pump) of the parietal cells thus reducing acid secretion. Indications: reflux esophagitis, duodenal ulcers, hypersecretory states Indications: reflux esophagitis, duodenal ulcers, hypersecretory states Side Effects: Constipation (few side effects) Side Effects: Constipation (few side effects) Omeprazole interacts with warfarin, phenytoin and diazepam Omeprazole interacts with warfarin, phenytoin and diazepam

Dysmotility Agent Metoclopramide (Reglan) Metoclopramide (Reglan) MOA: increases rate of gastric emptying by an unknown mechanism MOA: increases rate of gastric emptying by an unknown mechanism Indications: reflux esophagitis, gastroparesis, pre-op gastric emptying Indications: reflux esophagitis, gastroparesis, pre-op gastric emptying Side Effects: diarrhea, constipation, can cause extra-pyramidal side effects due to dopamine antagonism (elderly and children) Side Effects: diarrhea, constipation, can cause extra-pyramidal side effects due to dopamine antagonism (elderly and children) Increases the toxicity of antipsychotics Increases the toxicity of antipsychotics

Mucosal Protectant Misoprostol Misoprostol MOA: increases bicarbonate and mucin release in the GI tract and reduces acid secretion MOA: increases bicarbonate and mucin release in the GI tract and reduces acid secretion Indications: prevention of ulcers caused by aspirin and other NSAIDS Indications: prevention of ulcers caused by aspirin and other NSAIDS Side Effects: Abortion (uterine contraction), diarrhea, abdominal pain, flatulence Side Effects: Abortion (uterine contraction), diarrhea, abdominal pain, flatulence Contraindications: PREGNANCY!!!! Contraindications: PREGNANCY!!!! Is a prostaglandin analog Is a prostaglandin analog

Antidiarrheal Agents Opiates Opiates Diphenoxylate and Atropine (Lomotil) Diphenoxylate and Atropine (Lomotil) MOA: diphenoxylate is an agonist at opiate receptors in the GI tract and atropine blocks muscarinic receptors. Both of these actions inhibit peristalsis MOA: diphenoxylate is an agonist at opiate receptors in the GI tract and atropine blocks muscarinic receptors. Both of these actions inhibit peristalsis Indications: Diarrhea Indications: Diarrhea Side Effects: few such as constipation, abdominal/bowel distention Side Effects: few such as constipation, abdominal/bowel distention Contraindications: Parasitic or bacterial infections, obstructive jaundice Contraindications: Parasitic or bacterial infections, obstructive jaundice Increased risk of paralytic ileus with antimuscarinics Increased risk of paralytic ileus with antimuscarinics Loperamide (Imodium) Loperamide (Imodium) No drug interactions No drug interactions Treat OD with Naloxone Treat OD with Naloxone

Antidiarrheal Agents Absorbents Absorbents Bismuth Subsalicylate (Pepto-Bismol) Bismuth Subsalicylate (Pepto-Bismol) MOA: absorbs toxins produced by bacteria and other GI irritants MOA: absorbs toxins produced by bacteria and other GI irritants Indications: Diarrhea, prophylaxis for traveler’s diarrhea Indications: Diarrhea, prophylaxis for traveler’s diarrhea Side Effects: Impaction Side Effects: Impaction Contraindications: Aspirin sensitivity Contraindications: Aspirin sensitivity Potentiates oral anticoagulants Potentiates oral anticoagulants Kaolin/Pectin (Kaopectate) Kaolin/Pectin (Kaopectate) MOA: adsorbent and protection that is of questionable efficacy MOA: adsorbent and protection that is of questionable efficacy Indications: diarrhea Indications: diarrhea Side effects: may increase potassium loss or interfere with absorption of drugs and nutrients Side effects: may increase potassium loss or interfere with absorption of drugs and nutrients Contraindications: obstructive bowel lesions Contraindications: obstructive bowel lesions

Antidiarrheal Agents Cholestyramine (Questran) Cholestyramine (Questran) MOA: absorbs bile salts (they cause diarrhea) and C. difficile toxin MOA: absorbs bile salts (they cause diarrhea) and C. difficile toxin Indications: Diarrhea caused by C. difficile or bile acids Indications: Diarrhea caused by C. difficile or bile acids Side Effects: constipation Side Effects: constipation Mainly used for lipid disorders Mainly used for lipid disorders

Inflammatory Bowel Agents Mesalamine and Sulfasalazine Mesalamine and Sulfasalazine MOA: anti inflammatory MOA: anti inflammatory Indications: inflammatory bowel syndrome, UC or Crohn’s Indications: inflammatory bowel syndrome, UC or Crohn’s Will cover more of this drug in a later chapter Will cover more of this drug in a later chapter

Bulk Forming Agents Psyllium (Metamucil) Psyllium (Metamucil) MOA: nondigested plant cell wall absorbs water into feces thus softening the stool MOA: nondigested plant cell wall absorbs water into feces thus softening the stool Indications: constipation, hard stools Indications: constipation, hard stools Side Effects: flatulence, impaction if the bolus is obstructed Side Effects: flatulence, impaction if the bolus is obstructed

Stimulant Laxatives Bisacodyl (Dulcolax) Bisacodyl (Dulcolax) MOA: increases water and electrolytes in feces and increases intestinal motility MOA: increases water and electrolytes in feces and increases intestinal motility Side Effects: continuous use may cause diarrhea Side Effects: continuous use may cause diarrhea

Milk of Magnesia Milk of Magnesia (saline solutions) Milk of Magnesia (saline solutions) MOA: magnesium or sodium salts are poorly absorbed and thus draw water into the lumen. MOA: magnesium or sodium salts are poorly absorbed and thus draw water into the lumen. High dose rids bowel of parasites and empties bowel preoperatively High dose rids bowel of parasites and empties bowel preoperatively Side Effects: precipitation of cardiac, renal, convulsive disorders or hypocalcaemia Side Effects: precipitation of cardiac, renal, convulsive disorders or hypocalcaemia

Castor Oil MOA: metabolized in the intestine to ricinoleate. It is a surfactant which decreases water and electrolyte absorption and increases motility MOA: metabolized in the intestine to ricinoleate. It is a surfactant which decreases water and electrolyte absorption and increases motility Side Effects: cramps. Chronic use must be avoided due the risk of dehydration, electrolyte imbalance and nerve damage Side Effects: cramps. Chronic use must be avoided due the risk of dehydration, electrolyte imbalance and nerve damage

Polyethylene Glycol (MiraLax) MOA: hyperosmolarity draws water into the colon MOA: hyperosmolarity draws water into the colon Side Effects: cramps, N, bloating Side Effects: cramps, N, bloating

Lactulose (Chronulac) MOA: Hyperosmolarity draws water into the colon. Gets metabolized in the intestine to lactate which acts as a laxative osmotically and by lowering the pH MOA: Hyperosmolarity draws water into the colon. Gets metabolized in the intestine to lactate which acts as a laxative osmotically and by lowering the pH Side Effects: cramps, flatulence, N/V Side Effects: cramps, flatulence, N/V

Mineral Oil MOA: Lubricates feces and prevents absorption of water from feces MOA: Lubricates feces and prevents absorption of water from feces Side Effects: anal leakage and irritation, reduces vitamin absorption Side Effects: anal leakage and irritation, reduces vitamin absorption Can develop aspiration pneumonitis with oral administration Can develop aspiration pneumonitis with oral administration

Docusate (Colace) MOA: improves penetration of water and fat into feces MOA: improves penetration of water and fat into feces Side Effects: diarrhea, abdominal cramps. Side Effects: diarrhea, abdominal cramps. It increases the absorption of mineral oil so do not use together with mineral oil It increases the absorption of mineral oil so do not use together with mineral oil

Obesity Management Orlistat (Xenical) Orlistat (Xenical) MOA: reversible lipase inhibitor therefore it inhibits the absorption of fats from the intestine MOA: reversible lipase inhibitor therefore it inhibits the absorption of fats from the intestine Should be accompanied by a balanced reduced calorie diet Should be accompanied by a balanced reduced calorie diet Multivitamin supplements are needed because vitamin absorption is decreased by the drug Multivitamin supplements are needed because vitamin absorption is decreased by the drug Patient will have fatty/oily stool Patient will have fatty/oily stool