GIT Flashcards
Which of the following drugs is not an antiemetic?
A Diphenoxylate
B Dexamethasone
C Ondansetron
D THC
A
Explanation
Diphenoxylate is a prescription opioid agonist that has no analgesic properties in standard doses. It is used as an antidiarrheal agent. However in higher doses there are CNS effects and this leads to dependence. Atropine is added in small doses (too low to have a significant antidiarrheal effect) but to discourage overdose of diphenoxylate. The anticholinergic properties of atropine may contribute to the antidiarrheal action. Chemicals, which work at the chemoreceptor trigger zone, are ACH, serotonin, dopamine, substance P and THC
Extra: THC (Delta 9 - TetraHydroCannabinol) is used as an antiemetic in patients undergoing chemotherapy. Dexamethasone - is an effective antiemetic drug, unclear mechanism. Ondansetron is 5HT3 blocker at CTZ, effective antiemetic.
Antiemetics
D2 receptor blockers- prochlorperazine, 5HT3 receptor blockers-ondansetron, antimuscarinic-hyoscine and scopolamine, antihistamines-diphenhydramine.
Regarding metoclopramide, which of the following statements is correct?
A It is a dopamine agonist
B It decreases ileal peristalsis
C It decreases the tone of the lower oesophageal sphincter
D It increases gastric emptying
D
Explanation
Metoclopramide is a prokinetic that aids gastric emptying and promotes peristalsis. It is a dopamine antagonist. It also increases lower oesophageal sphincter tone
Regarding cisapride, which of the following statements is correct?
A It increases pancreatic secretions
B It raises lower oesophageal sphincter pressure
C It slows gastric emptying
D It delays oesophageal clearance
B
Explanation
Cisapride is a parasympathomimetic acting on 5-HT4 agonist and was used in the treatment of gastro-oesophageal reflux and motility disorder. Due to its association with increased cardiovascular events that were attributed to the inhibition of cardiac hERG K channels, which resulted in QT prolongation in patients, it is only prescribed in the USA for compassionate reasons
Extra:
increases acetylcholine release in the enteric nervous system (specifically the myenteric plexus). This results in increased tone and amplitude of gastric (especially antral) contractions, relaxation of the pyloric sphincter and the duodenal bulb, and increased peristalsis of the duodenum and jejunum resulting in accelerated gastric emptying and intestinal transit.
Regarding cimetidine, which of the following statements is correct?
Your answer was correct
A It never causes gynaecomastia
B It inhibits cytochrome P450
C It blocks both H1 and H2 receptors
D T1/2 is 22 hours
B
Explanation
Cimetadine blocks H2 receptors and not H1. Half life is 1.9hrs. Bioavailability of approximately 62%. VD 70L/Kg. Gynaecomastia is one of the many side effects (others include mental state changes, and galactorrhea in women; impotence in men). They rarely cause blood dyscrasias
Which receptor action is required for an antiemetic to be effective?
A Neurokinin receptor agonism
B Nicotinic receptor antagonism
C Serotonin receptor agonsim
D Dopamine receptor antagonsim
D
Explanation
Metoclopramide is a D2 dopaminergic receptor ANtagonist. Ondansetron is a 5HT3 serotonin receptor ANtagonist.
Which is of the following is a stool softener?
A Psyllium
B Lactulose
C Senna
D Docusate
D
Explanation
Laxatives
Bulk forming: psyllium, methylcellulose- both are natural plant products and polycarbophil is a synthetic compound
Stool softeners: docusate, glycerin suppository and mineral oil
Osmotic laxatives: magnesium hydroxide, sorbitol, lactulose, magnesium citrate, sodium phosphate and polyethylene glycol.
Stimulants: aloe, senna, cascara, biscodyl
Chlorie channel activator: lubiprostone (increase chloride rich fluid secretion into the intestine)
Opioid receptor antagonists: methylnaltrexone and alvimopan (antagonizes the opioid causing intestinal dismotility)
Serotonin receptor agonists: tegaserod and prucalopride (promotes peristaltic activity, proximal bowel contraction and distal bowel relaxation)
Guanylate cyclase C agonists: linaclotide (stimulates intestinal fluid secretion)
Which is true about omeprazole?
A They are administered as acid stable active drugs
B Blocks both fasting and meals stimulated acid secretion
C Needs dose alteration in patients with renal insufficiency
D Is safe for long term use in pregnancy
B
Explanation
Omeprazole has a bioavailability of 40-65%. A half life of 0.5-1hr. It undergoes rapid first pass and systemic hepatic metabolism and has only negligible renal clearance. Dose reduction is not required for patients with renal insufficiency or mild to moderate liver impairment. PPIs are administered as inactive acid labile prodrugs which are enteric coated to protect them form destruction in the gastric lumen. After passing into the alkaline intestinal lumen, the coating dissolves, the lipophilic weak base prodrug rapidly cross the lipid membrane into acid compartments e.g. the parietal cell. In the parietal cell’s acid medium they become activated. Proton pump inhibitors block fasting and meal stimulated secretion. In standard dosings PPI inhibit 90-98% of 24hr acid secretion. PPI are safe and do not have proven teratogenicity in animals. However, safety in pregnancy has not been well established.
Additional explanation: PPIs are unable to block inactive/quiescent pumps and only block actively secreting pumps (in the fasted and unfasted state), so can take days to become effective, and IV formulation should be given as an infusion rather than bolus doses
Which of the following anti-emetics do not cause exta pyramidal side effects?
A Promethazine
B Droperidol
C Ondansetron
D Metoclopramide
C
Explanation
The 5HT3 receptor antagonists (ondansetron, granisetron, dolsetron and palonosetron) are generally well tolerated. Commonly reported side effects are headache, dizziness and constipation. All agents cause a small but statistically significant QT prolongation. Dolsetron seems to be the agent with the greatest risk and should not be administered to patients with prolonged QT. These drugs do not cause any extra pyramidal side effects. These antagonists do NOT inhibit dopamine or muscarinic receptors. They do not have effects on esophageal or gastric motility but may slow colonic transit.
Note: droperidol may prolong the QT interval as well
Omeprazole reduces acid secretion through reduction of:
A Na/K ATPase
B Secretion
C Gastrin
D H/K ATPase
D
Explanation
Proton pump inhibitors irreversibly inhibit the H/K ATPase in the parietal cell canaliculus.
A patient with known liver cirrhosis presents with hepatic encephalopathy. He is on acetazolamide, digoxin, ACE-I and frusemide. Which medication is the most likely cause of his encephalopathy?
A Frusemide
B Digoxin
C Acetazolamide
D ACE-Inhibitor
C
Explanation
Carbonic anhydrase inhibitor–induced alkalinization of the urine decreases urinary excretion of NH4+ (by converting it to rapidly reabsorbed NH3) and may contribute to the development of hyperammonemia and hepatic encephalopathy in patients with cirrhosis.
