Download Gastrointestinal vivas

GASTROINTESTINAL VIVAS
2009-1, 2006-2
What is the mechanism of action of ondansetron
- Selective 5-HT3 receptor antagonists both peripheral in intestinal vagal afferents and central in
chemoreceptor trigger zone and vomiting center in lateral medulla
What are the clinical uses of ondansetron
- Chemotherapy-induced nausea and vomiting e.g. 8 mg every 8 -12 hours
- Postoperative and post radiation nausea and vomiting
- Other indications: acute or chronic medical conditions or gastroenteritis (not well evaluated)
Name some side-effects of ondansetron
- Headache, dizziness and constipation
- Small prolongation of QT interval
What are the routes of administration and dose of ondansetron?
- Similar doses, 4-8mg, oral tablet or wafer, IV
2008-2
Describe the mechanism of action of metoclopramide?
- Dopamine antagonist (D2 receptors)
- Central w/ anti-nausea/emetic effect on the Chemoreceptor Trigger Zone (area postrema)
Peripheral blockade of GI dopamine receptors allowing cholinergic smooth muscle stimulation w/
increased oesophageal peristaltic amplitude, increases lower oesophageal sphincter pressure
and enhanced gastric emptying
List the adverse effects of metoclopramide?
- Relate to central dopamine antagonist action
- Restlessness, drowsiness, insomnia, anxiety, agitation
- Extrapyrimadal effects: dystonias, akathisia, parkinsonian features
- Risk of tardive dyskinesia with chronic use
- Hyperprolactinemia (galactorrhoea, gynecomastia, impotence, menstrual disorders)
2008-1, 2005-1
What classes of drug can be used as antiemetics?
1. Serotonin 5-HT3 antagonists: the “trons”
2. Phenothiazines: prochlorperazine, promethazine
3. Butyrophenones: haloperidol
4. Substituted benzamides: metoclopramide, a D2 antagonist
5. H1 antihistamines: diphenhydramine, cyclizine
6. Anticholinergics: hyoscine
7. Others: Benzos, Cannabinoids, Corticosteroids
List and explain the adverse effects of prochlorperazine ?
- Acute dystonia (dopamine blockade)
- Sedation (antihistamine effects)
- Anticholinergic effects (antimuscarine effects)
- Allergy
2008-2, 2005-2
Using examples, outline the mechanism of action of the various types of laxative?
Bulking
Hydrophyllic colloids, agar, psyllium seed, bran, kiwifruit (high in fibre)
(reflex contaction)
Softening
Permit water and lipids to penetrate: Docusate, glycerine
Osmotic
Lactulose, Magnesium citrate and magnesium hydroxide, polyethylene
glycol, sorbitol
Stimulant
(act early) castor oil -(act late) cascara, senna, aloes (contain emodin
alkaloids which are liberated after absorption from the intestine and
excreted in the colon) -(prolonged action by enterohepatic circulation)
phenolphthalein & biscodyl
Cl- channel activator
Lubiprostone
Opioid receptor
Methylnaltrexone
antagonist
5HT-3 agonist
Tegaserod
Polyethylene glycol is used as a prep for endoscopic procedures. What features make it safe
for all patients? 2005-2
- Balanced
- Osmotically active sugar (PEG) with NaCl, NaHC03, KCl
- No significant osmotic shifts. Best ingested rapidly for bowel cleansing
2008-1
Explain the rationale for the use of octreotide in upper gastrointestinal bleeding
- Octreotide reduces splanchnic blood flow, (?By glucagon release inhibition) therefore reduces
portal venous pressure
- This reduces blood loss from bleeding oesophageal varices and in some cases of severe
duodenal ulcer related bleeding
What are the pharmacokinetic differences between octreotide and somatostatin?
- Octreotide is a somatostatin analogue that has a longer half life than somatostatin (1.5hrs vs 3
min) so can be given as an IV infusion or subcutaneously
(Supp Question – What other agents may be useful in the prevention and treatment of upper
GI bleeding)
- PPIs – omeprazole
- H2 anatagonists – cimetidine, ranitidine
- Vit K, prothrombinex, FFP
- Tranexamic acid
.