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Compendium June 2002 Drug Therapy/GI Disease 455 Table 3. Antisecretory Drugs Drug Dose Comment Cimetidine Dogs and cats: 5–10 mg/kg PO q6–8h Give IV dose slowly over 30–40 min or 10 mg/kg IV q6h in dogs and cats; cytochrome P450 microsomal enzyme inhibitor Ranitidine Dogs and cats: 0.5–2 mg/kg PO, IV, IM, or SC q8–12h No serious side effects reported Famotidine Dogs and cats: 0.5–1.0 mg/kg PO or IV q12–24h No serious side effects reported Nizatidine Dogs: 5 mg/kg/day PO No serious side effects reported Omeprazole Dogs: 0.5–1.0 mg/kg/day PO Achlorhydria, diarrhea, and transient fluctuations in liver enzymes reported trol vomiting, although the exact mechanism of action is not understood. These agents may have a synergistic effect when used with other antiemetics, such as metoclopramide, particularly when used in chemotherapy patients. Because of the side effects of gastric, duodenal, and colonic ulceration, the use of glucocorticoids for vomiting is not recommended. Barbiturates and Benzodiazepines Barbiturates (e.g., phenobarbital) and benzodiazepines (e.g., diazepam) are sedatives that are used to control psychogenic and behavioral vomiting by acting on the higher centers of the brain. This type of vomiting, however, is not well documented in veterinary medicine. Anticholinergics Anticholinergics (e.g., atropine) are centrally acting antiemetics that block cholinergic transmission as well as muscarinic receptors in the emetic center. Many anticholinergics (e.g., glycopyrrolate, propantheline, meth-
456 Small Animal/Exotics Compendium June 2002 Table 4. Cytoprotective Drugs and Antacids Drug Dose Comment Aluminum magnesium hydroxide Dogs and cats: 2–10 ml PO q2–4h Preferred combination to avoid side effects Aluminum carbonate gel Dogs and cats: 10–30 mg/kg PO Can cause diarrhea, nausea, GI upset, q8h with meals constipation, and hypophosphatemia Aluminum hydroxide Dogs and cats: 30–90 mg/kg PO Binds bile salts and phosphorus; q8–24h with meals inactivates pepsin; can cause constipation Magnesium hydroxide Dogs: 5–30 ml PO q8–24h; Can cause diarrhea; avoid cats: 5–10 ml PO q8–24h magnesium-based products in patients with renal failure Calcium carbonate Dogs: 50–75 mg/kg divided daily Can cause metabolic alkalosis, q8–12h PO hypercalcemia, calciuria, hypophosphatemia, and constipation Misoprostol Dogs and cats: 2–5 µg/kg PO q6–8h Prevents NSAID-induced gastric ulcers Sucralfate Dogs 15 kg: 1-g tablet q6–8h; before or after other drugs (may bind cats: 1 /4 - to 1 /2-g tablet q8–12h with other medications if administered together) scopolamine [not recommended for use in cats], and isopropamide) do not cross the blood–brain barrier; therefore, they act peripherally. Peripheral actions that prevent vomiting are due to inhibition of afferent vagal stimulation, relaxation of smooth muscle, and inhibition of GI secretions. Unfortunately, the limiting effect is that they promote delayed gastric emptying and decreased intestinal motility, causing GI overdistention, which may in itself cause vomiting. They also inhibit the actions of such drugs as metoclopramide, cisapride, and opioids that are dependent on cholinergic activity in ganglia or smooth muscle. Because this inhibition limits their usefulness, anticholinergics are not usually recommended. 1 Antihistamines Antihistamines are used to control vomiting caused by motion sickness or inner-ear disease, which is mediated by the vestibular apparatus. Cyclizine hydrochloride, meclizine hydrochloride, or diphenhydramine hydrochloride may control vomiting for several hours. 2 Side effects of antihistamines include drowsiness and dry mouth. GASTRIC ANTISECRETORY DRUGS Gastric antisecretory drugs are most commonly used to treat gastric inflammation and ulceration (Table 3). Gastric ulceration caused by drugs, toxins, trauma, immune-mediated disease, or neoplasia may be treated by reducing the acidity of gastric secretions. Esophagitis caused by foreign bodies, ingestion of caustic substances, gastric reflux during anesthesia, and chronic vomiting are also treated by reducing gastric acidity and reflux of gastric fluid. H2-Receptor Antagonists H2-receptor antagonists (H2 blockers), which are relatively inexpensive, are the most widely available drugs that reduce hydrogen ion content of gastric secretions and the amount of pepsin induced by other secretory enzymes. In addition, these drugs, particularly the newer ones (e.g., ranitidine, nizatidine), may also promote gastric prokinetic activity due to anticholinesterase properties. The potency and duration of action of H2 blockers are rated as follows: Famotidine > ranitidine > cimetidine2 Gastric motility potency studied in guinea pig muscle is rated as follows: Nizatidine = ranitidine > cimetidine > famotidine7 Cimetidine inhibits the cytochrome P450 microsomal enzyme system in the liver and thus impairs the metabolism of other drugs and should be avoided in animals with liver disease or when being used with other medications that are metabolized by the liver. Rebound hypersecretion of gastric acid is believed to be the cause for relapse of gastroduodenal ulcers in humans when H 2 blockers are discontinued. 8 Most H 2 blockers are available over the counter, making dispensing and refilling them easy. Proton Pump Inhibitors Proton pump inhibitors are substituted benzimida-
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