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Compendium June 2002 Drug Therapy/GI Disease 457 Table 5. Protectants and Adsorbents Drug Dose Comment Kaolin–pectin Dogs and cats: 1–2 ml PO q2–6h Used for nonspecific treatment of diarrhea Bismuth subsalicylate Dogs: 0.25–2 ml/kg PO q4–6h; cats: Cats should not receive frequent or 0.25 ml/kg PO q4–6h high doses because of possible salicylate toxicity Activated charcoal Dogs and cats: 1–4 g/kg PO slurry, as Best if used within the first hour of needed (1 g/5 ml water); 6–10 ml/kg PO ingestion; slurry and suspension are suspension, as needed more absorptive than tablets Cholestyramine Dogs: 200–300 mg/kg PO q12h, Can cause hypochloremic acidosis, as needed steatorrhea, decreased fat-soluble vitamin absorption, and hypoproteinemia zoles and a new class of antisecretory drugs. They are potent antagonists of the H + /K + ATPase proton pump, which is the final step to secretion of hydrogen ions at the apex of the parietal (oxyntic) cell. Omeprazole is the most commonly used proton pump inhibitor in veterinary medicine and is reported to be 30 times more potent than the H 2 blocker cimetidine. 9 Omeprazole is formulated as encapsulated entericcoated granules that are dissolved in the alkaline con- tents of the small intestine. The drug is absorbed into the systemic circulation and concentrated in the acidic environment of the parietal (oxyntic) cell, where it is converted to the inhibitor drug. There is a lag period of 3 to 5 days for the drug to accumulate in the parietal cell before maximum effects are seen. After this time, low serum concentrations will maintain the effect with once-daily dosing. Omeprazole is considered superior to H 2 blockers in the treatment of
458 Small Animal/Exotics Compendium June 2002 Table 6. Motility-Modifier Drugs Drug Dose Comment Metoclopramide Dogs and cats: 0.1–0.5 mg/kg PO or SC q8h LES, stomach, and small intestinal effects Domperidone Dogs and cats: 0.1–0.5 mg/kg IM or IV q12h LES, stomach, and small intestinal effects; or 2–5 mg/kg PO q12h not currently available in the United States Cisapride Dogs: 0.1–0.5 mg/kg PO q8–12h; cats: 2.5–5 LES, stomach, small intestinal, and colon mg PO q8–12h effects Diphenoxylate Dogs: 0.1–0.2 mg/kg or 2.5–10 mg PO q8h; Narcotic that contains atropine to hydrochloride cats: 0.05–0.1 mg/kg PO q12h or 0.6–1.2 mg prevent abuse; controlled substance; PO q8–12h used to treat diarrhea Loperamide hydrochloride Dogs: 0.08–0.20 mg/kg PO q8–12h; cats: Available over the counter due to lack of 0.1–0.3 mg/kg PO q12–24h or 0.08–0.16 blood–brain barrier transmission; used mg/kg PO q12h to treat diarrhea Erythromycin Dogs and cats: 0.5–1.0 mg/kg PO q8h Give after meals; LES, stomach, and small intestinal effects Ranitidine Dogs and cats: 0.5–2 mg/kg PO, IV, IM, or SC q8–12h Stomach, small intestinal, and colon effects Nizatidine Dogs: 5 mg/kg/day PO Stomach, small intestinal, and colon effects Misoprostol Dogs and cats: 2–5 µg/kg PO q6–8h Colon effects; may be effective in refractory constipation LES = lower esophageal sphincter. esophageal and gastric inflammation and ulceration. Although the high cost of omeprazole may limit its use, the shorter recovery period and more successful outcome in severe cases may justify the expense. Side effects in animals are not reported when omeprazole is used less than 8 weeks. 10 CYTOPROTECTIVE DRUGS AND ANTACIDS Cytoprotective drugs are commonly used in patients to decrease gastric acidity (Table 4). Antacids Antacids chemically neutralize hydrochloric acid in the gastric lumen, resulting in the generation of chlorides, water, and carbon dioxide. Some formulations (e.g., aluminum hydroxide) may also bind bile salts and inactivate pepsin. Some products induce local synthesis of the mucosal protectants, prostaglandins, and sulfhydryls. The duration of action of antacids is usually about 1 to 2 hours and is extended when food is present because of increased gastric pH. Administration of these drugs with food is required every 4 to 6 hours to prevent a gastric acid rebound effect, which occurs because the increased pH in the antral lumen stimulates increased serum gastrin levels. Aluminum, magnesium, and calcium salts can be used alone or in combination. In addition to antacid properties, aluminum salts absorb bile acids and pepsin and stimulate local prostaglandin production; however, they may cause constipation. Aluminum salts also bind phosphate, thereby reducing phosphate absorption. They are often used to manage patients with renal failure but can cause hypophosphatemia with prolonged use. Products containing magnesium are better at raising the gastric pH than are aluminum products. Unabsorbed magnesium salts, however, act as a laxative and can cause diarrhea. Therefore, a combination of aluminum and magnesium is the preferred antacid. Calcium carbonate is a potent and fast-acting antacid, but prolonged use may cause metabolic alkalosis, gastric-acid rebound, hypercalcemia, calciuria with metastatic calcification and urolithiasis, hypophosphatemia, and constipation. 11 Misoprostol Other drugs that have antisecretory properties are prostaglandin analogues, but they are not as effective as H 2 blockers in decreasing intraluminal gastric pH. Misoprostol, a prostaglandin E 1 analogue, is an antisecretory drug as well as a cytoprotectant. Hydrochloric acid production is decreased by interaction with a basolateral membrane receptor, which decreases cyclic adenosine monophosphate, thus decreasing protein kinase activity and hydrogen ion concentration. 12 Misoprostol increases mucus and bicarbonate secretion and enhances the epithelialization of the mucosa and
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