Gastrointestinal Drugs

Question 1

Antiemetics - Metoclopramide

Answer 1

*Metoclopramide
—central and local antiemetic effects:
-central=blocks dopamine in the chemoreceptors-trigger zone
-local=increases lower esophageal tone while decreasing pyloric sphincter tone and stimulate motility of upper GI tract
—PO, parenterally or CRI
—Contraindicated in:
-GI obstruction 
-perforation 
-pheochromocytoma
—behavioral changes seen 
 -GI stimulatory drug

Question 2

Chlorpromazine and prochlorperazine

Answer 2

• Centrally acting antiemetic
• both phenothiazines
• antiemetic
• sedative
• hypotensive effects
• Long acting (elimination half life ~3 hours)
• overdose likely due to wide dose range
• no reversal
• treat supportively
• limited use in ICU
• not to be given within one month of worming - potentiates effects

Question 3

Ondansetron and dolasetron

Answer 3

• serotonin antagonists
• central and peripheral antiemetic effects
• PO and injectable form
• Can be administered in conjunction with other antiemetics
• Metabolised in liver but safe to give with liver disease
• Dolasetron - dose once daily

Question 4

Maropitant

Answer 4

• Neurokinin-1 receptor antagonist
• inhibit substance P = suppresses both peripherally and Centrally mediated emesis
• SQ (1mg/kg)or PO (2-8mg/kg)
• SQ injection = painful
• Maximum 5 day regimen with a 48 hour washout period RECOMMENDED
• due to low CYP-450 enzyme capacity

Question 5

GI protectants

Answer 5

H2 antagonist:

• Cimetidine
• inhibits hepatic microsomal enzyme system = decreased metabolism, prolonged half life and increased serum levels of many drugs
• caution use with: Beta blockers, lidocaine, procainamide, benzodiazepines, metronidazole, theophylline, and warfarin
• hepatic effects can used therapeutically in overdose situation of drugs with active and toxic metabolites such as: acetaminophen (contraindicated in cats)
• Famotidine
• Ranitidine
• Nizatidine
• inhibits histamine release in parietal cells = reduction in gastric acid production
• Ranitidine and nizatidine = prokinetic effects
• All H2 antagonist can cause bradycardia if given too rapidly IV
• cleared through kidneys
• hence patients with renal insufficiencies = lower doses given and increase dosing intervals

Question 6

Proton pump inhibitors (PPIs)

Answer 6

• replaced H2 antagonist as antiulcer meds of choice
• superior in suppressing acid production
• decreased dosing frequency
• Omeprazole
• binds to secretory surface of parietal cells
• inhibits transport of hydrogen ions into stomach
• inhibits microsomal enzymes = reduce hepatic clearance of some drugs
• dosed once daily = reducing cost albeit expensive
• Other kinds:
• Lansoprazole
• Rabeprazole
• Pantoprazole
• esomeprazole
• can affect absorption of drugs requiring acidic environment
• stagger drugs
• potential bacterial overgrowth in intestines due to altered acidity

Question 7

Misoprostol

Answer 7

• prostaglandin analog
• reduces gastric acid production
• cytoprotective effect on gastric mucosa
• increases turnover of mucosal cells and improves blood supply = accelerate healing of gastric ulcers
• VERY helpful in treating NSAID-induced ulcers
• use gloves due to abortions cause
• side effects:
• GI distress
• absorbed rapidly PO
• presence of food or antacids will delay absorption
• metabolised by liver into active metabolites and further into inactive metabolites excreted in the urine

Question 8

Sucralfate

Answer 8

• PO
• intyeracts with stomach acids to form paste like barrier on ulcer sites
• tx of oral, esophageal, gastric and duodenal ulcers
• affects absorption of other PO drugs
• give on an empty stomach two hours apart from other medications