Drugs acting on the Gastrointestinal Tract:- Gastrointestinal diseases is a common clinical problem in veterinary practice, and accurate diagnosis is essential for effective therapy

Nonspecific therapy includes A. Correction of fluid and electrolyte balance. Prolonged vomiting or diarrhea produces dehydration, electrolyte loss, and disturbances in acid-base balance that must be corrected by parenteral fluid therapy. B. Rest of the gastrointestinal tract. Fasting for hours

C. Alleviation of visceral pain Mild visceral pain may be alleviated by alimentary protective or absorbents (e.g., aluminum or magnesium silicates, kaolin-pectin, bismuth salts). These agents may reduce pain by reducing gastric acidity, coating inflamed mucosa, or absorbing noxious agents in the lumen.

APPETITE STIMULANTS. In appetence or anorexia is common in disease state, and the resultant malnutrition can delay recovery and may exacerbate the underlying disease. Various drugs are used for the short-term stimulation of appetite. 1. Benzodiazepines (e.g., diazepam, oxazepam) 2. Cyproheptadine a. Mechanism of action. Cyproheptadine acts as histamine (H 1 )antagonist.

3. Glucocorticoids (e.g., prednisolone, dexamethasone) Adverse effects (a) Immunosuppression may delay recovery from the underlying disease. (b) Gastric ulcers may result from decreased gastric mucus production. 4. Zinc is essential for the sensation of taste; therefore, zinc supplements may in­crease appetite in zinc- deficient animals.

****Antacids*** reduce the hydrochloric acid content of the stomach by inhibiting acid secretion, neutralizing acid, or coating and protecting the gastric mucosa. **Acid secretion inhibitors 1. Histamine (H 2 )-blockers (e.g., cimetidine, ranitidine) Mechanism of action. H 2 -blockers competitively block the H 2 receptors on parietal cells, thereby de­creasing hydrochloric acid secretion.

2. Proton pump inhibitors (e.g., omeprazole) Mechanism of action. Proton pump inhibitors reduce hydrogen secretion by in­hibiting the H + -K-ATPase pump on the luminal membrane of parietal cells.

Therapeutic uses (1) Omeprazole is used to limit acid secretion in gastritis, gastric ulcers, and esophagitis. Drug interactions. Omeprazole inhibits hepatic microsomal metabolism and may prolong the actions of drugs requiring hepatic metabolism.

Locally acting antacids 1. Preparations a. Aluminum salts (e.g., aluminum hydroxide, aluminum carbonate, aluminium silicate) are the most common preparations. b. Magnesium salts [e.g., magnesium oxide (milk of magnesia),magnesium trisilicate] have a laxative effect in addition to their potent antacid activity.

Adverse effects Constipation. Aluminum salts increase fecal phosphate excretion, which tend to produce constipation. Combination with laxative magnesium salts offset this effect.

EMETICS indications for emetics. Emetics are used in conscious animal to induce elimination of noncorrosive poisons or prior to the induction of general anesthesia. They generally remove less than 80% of the stomach contents. Centrally acting emetics 1. Apomorphine Mechanism of action. Apomorphine induces vomiting by stimulating the chemoreceptor trigger zone

2. Xylazine: induces vomiting, Vomiting occurs within 2-5 minutes. **Peripherally acting emetics** 1. Preparations: a. Sodium chloride is administered as saturated solution. b. b. syrup of ipecac contains emetine alkaloid. c. Copper sulfate (1%), zinc sulfate (1%), and hydrogen peroxide (3%) are infrequently used.

ANTIEMETICS 1. Prolonged vomiting leads to electrolyte and acid-base imbalances and dehydration. 2. Diagnosis and treatment of the primary cause of vomiting should precede administration of the antiemetic. The most frequent causes of prolonged vomiting are.

a. Inflammation, distention, or the presence of chemicals or drugs in the gastrointestinal tract b. Labyrinthine disease or motion sickness c. Inflammation, edema, or tumors of the CNS d. Stimulation of the chemoreceptor trigger zone by drugs, bacterial endotoxins or toxic endogenous metabolites (e.g., urea)

Phenothiazines (e.g., acepromazine, chlorpromazine, promazine) 2. Metoclopramide a. Mechanism of action Central action results from blockade of chemoreceptor trigger zone.

3. Butyrophenones (e.g., droperidol, haloperidol). Therapeutic uses. Butyrophenones are used to control vomiting resulting from cancer chemotherapy.

LAXATIVES AND CATHARTICS. Osmotic cathartics 1. Preparations a. Magnesium sulfate, magnesium oxide b. Sodium sulfate. c. Polyethylene glycol electrolyte solutions.

*mechanism of action:- Osmotic cathartics are non absorbable that osmotically retain water in the intestinal lumen. therapeutic use. Osmotic cathartics are the cathartics of choice for elimination of poison 2. Irritant cathartics (e.g., castor oil, aloe, senna, cascara sagrada), Chemistry. Irritant cathartics are plant derivatives.

3. Bulk laxatives (e.g., methylcellulose, agar, psyllium, wheat bran) 4. Lubricants. Mineral oil (liquid petrolatum) and white petrolatum lubricate and soften feces. 5. Surfactants. Docusate is an anionic surfactant that acts in the large bowel to hydrate and soften feces by an emulsifying action.