GI DRUGS Flashcards
what is the mechanism of action for antacids?
alkaline ions to neutralise stomach acid
what ions are normally present in antacids?
bicarbonate or hydroxide ( magnesium or aluminum salts)
name 2 conditions antacids are used in
GORD for symptomatic relief of heart burn
Dyspepsia–> short term relief
name a contraindication of magnesium-containing antacids
renal disease
when shouldn’t aluminium-containing antacids be administered?
gastric obstruction (inhibit gastric emptying)
which electrolytes does gaviscon contain?
aluminium
magnesium
what are the side effects of aluminium-containing antacids?
constipation
what are the side effects of magnesium-containing antacids?
diarrhoea
why shouldn’t antacids be taken within 1-2 hours of other drugs?
alter GI transit time so can affect absorption of other drugs
Antacids increase the alkalinity of urine and therefore increase the excretion of two drugs via urine.
What are these two drugs?
Aspirin and lithium
give an example of a H2 antagonist
ranitidine (trade name zantac)
how do H2 antagonists work?
competitive antagonists of histamine for H2 receptor on the gastric parietal stomach cells which reduces acid production
name 2 instances when H2 antagonists are used
dyspepsia
peptic ulcer disease
GORD
name 3 ways H2 antagonists can be administered
tablets
IM
IV
when is the only instance H2 antagonists are contraindicated?
hypersensitivity
What are the common side effects of H2 antagonists
Diarrhea
dizziness
headaches
name 2 circulatory side effects of H2 antagonists
bradycardia
arrhythmia
name 2 other side effects of H2 antagonists
agitation
fatigue
erythema multiforme
how can H2 antagonists interact generally with other drugs?
decrease GI absorption
what drug interaction with H2 antagonists can cause hyoprothrombinaemia?
warfarin (bleeding)
H2 antagonists increase plasma levels of which substance?
alcohol
give an example of a proton pump inhibitor
omeprazole
how do proton pump inhibitors work?
Permanent block of the parietal cell proton pumps (H+/K+-ATPase)
Stops H+ ions being produced and therefore gastric acid production
name 5 instances where PPIs are used
dyspepsia peptic ulcer disease H pylori GORD barrett's oesophagus gastritis gastrinoma
when in the day are proton pump inhibitors not meant to be taken?
with food
what is contraindications for PPIs?
hypersensitivity
Osteoporosis
name 2 GI side effects of PPIs
nausea
abdo pain
constipation
flatulence
which electrolyte imbalance can arise with PPIs?
hypomagnesaemia which can cause tetany or ventricle arrhythmia
name 2 other side effects of PPIs
headache dizziness fatigue anxiety rash
how do PPIs interact with cytochrome p450?
It is metabolised by it and inhibits the enzyme
how do PPIs affect the bioavailability of digoxin?
increase
give an example of a laxative
senna
how do bulk-forming/roughage laxatives work?
add bulk + water to stools which increases mass so can pass more easily= stimualates peristalsis
how do emollient laxatives work?
stool softeners with extra water & fat in stool
how do lubricant laxatives work?
coat stool in slippery lipid to aid passing
how do hyperosmotic laxatives work? give an example
draw water into stools maintaining its
volume and stimulating peristalsis
e.g. lactulose
how do stimulant laxatives work?
act on mucosa &; nerves to stimulate water secretion and peristalsis
Give examples of when
a) bulking laxative are used
b) osmotic laxatives are used
a) Constipation or faecal impaction (cannot increase fibre intake)
Mild chronic diarrhoea associated with IBS or divertiulitar diseae
b) Constipation and feacal impaction
Bowel prep prior to surgery and endoscopy
hepatic encalopathy
what are the 2 ways that laxatives can be administered, and what it the difference between them?
oral (works in 12hrs)
rectal (works w/i mins)
give 3 examples of when laxatives are contraindicated
intestinal obstruction= increae risk of perforation
Crohn’s
ulcerative colitis
ileus
What is a long term risk of laxative use?
dependance
what is melanosis coli? and what is it a complication of?
brown pigmentation of colonic wall
complication of laxatives
how do laxatives increase digoxin toxicity?
reduce serum potassium
give an example of an aminosalicylate
Mesalazine
Sulfasalazine
how do aminosalicylates work?
They release 5 aminosalicylic acid (5-asa)
Have anti inflammatory and immunosuppressive effects specifically on the gut (topically)
name 2 conditions aminosalicylates are used in?
Mesalazine used for mild to moderate ulcerative colitis
Sulfasalazine is a DMARD and used for RA
name 2 organ insufficiencies which would contra-indicate use of aminosalicylates
renal
hepatic
name 2 conditions that would contra-indicate use of aminosalicylates
active peptic ulcer haemorrhagic diathesis (tendency to bleed)
which drugs may reduce the effect of aminosalicylates?
antacids, H2 antagonists, PPIs= increase gastric PH
lactulose= lowers stool ph in colon
what drugs may cause toxicity of aminosalicylates
other 5-ASA derivatives
give an example of an antiemetic
metoclopramide and domperidone = stop nausea and vomiting
how do 5-HT3 receptor antagonist antiemetics work?
block serotonin receptors
when are dopamine antagonist antiemetics used?
neoplastic disease
radiation sickness
surgery
what kind of antiemetic is metoclopramide?
5-HT3 and dopamine antagonist (prokinetic effect)
name 2 other types of antiemetics
steroids
cannabinoids
antihistamines
which neurological disease could be worsened by use of dopamine antagonists?
Parkinson’s
give 3 mental health conditions that are contraindicated for antiemetics
depression
ADHD
restless leg syndrome
give a GI side effect of antiemetics
diarrhoea
which of these is not a neurological side effect of metaclopramide ?
1) tardive dyskinesia (involuntary movement)
2) migraines
3) extrapyramidal disorders
2) migraines
give 2 other side effects of antiemetics
tiredness
depression
restlessness
name 2 substances with which antiemetics produce a sedative effect?
alcohol
hypnotics
narcotics
tranquilliser
where do antiemetics reduce absorption?
which drug could this effect?
In the stomach
digoxin
where do antiemetics increase absorption?
name 2 drugs this could effect
small bowel
L dopa, tetracycline, cyclosporin, ethanol
name an antidiarrhoeal agent
loperamide
immodium
on which receptors do antidiarrhoeals act?
opioid receptor agonists - act on opioid receptors in mesenteric plexus
how does acting on opioid receptors act in an antidiarrhoeal fashion?
decrease activity & tone of smooth muscles in intestinal wall
increases time things stay in intestine so more water absorbed out of fecal matter
decreases mass movement
what reflex do antidiarrhoeals suppress?
gastro-colic (stretching of stomach stimulates colon movement)
what prevents antidiarrhoeal opioid receptor agonists crossing the blood brain barrier?
p-glycoprotein
give 3 examples when antidiarrhoeal agents used?
gastroenteritis
IBD
short bowel syndrome
travellers diarrhoea
which 3 conditions contra-indicate the use of antidiarrhoeals?
dysentery= especially if caused by e.coli can cause HUS acute UC exacerbating= can lead to toxic megacolon and perforation bacterial enterocolitis ( C.diff colitis)
name 3 organisms that cause bacterial enterocolitis
e coli
salmonella
c. diff
name 2 GI side effects of antidiarrhoeal agents
constipation
vomiting
increased risk of toxic megacolon
which drug should not be taken in conjunction with antidiarrhoeal agents?
quinidine - p-glycoprotein inhibitor
increases risk of drug crossing blood brain barrier
What can prolong use of PPI cause in a elderly patient?
Can increase the risk of bone fracture
What affect does omeprazole have on clopidogrel?
Due to its effect of p450 it reduces the anticoagulant effects and therefore alterantive PPI should be used
What affect on plasma levels does PPI have on nelfavir?
Reduces the plasma levels
Why is H2 antagonist not as effective of stopping acid production compared to PPI’s?
Histamine is one of many mediators of the proton pump so therefore it cannot completely suppress the pump while PPI’s can.
PPI’s can almostly completely stop acid production
Hypersensitivity to what other drug would be a contradiction to the use of aminosalicylates?
Aspirin hypersensitivity
What type of laxative is movicol?
Bulk forming laxative
What type of laxative is Senna?
Stimulant laxative
What is the effect of dopamine on the stomach and what receptor does it act on?
It acts on D2 receptor and is an important neurotransmitter in the gut, where it promotes
relaxation of the stomach and lower oesophageal sphincter and inhibits gastroduodenal coordination.
What is a GI contradiction of anti emetics?
Bowel obstruction
What effect does me metoclopramide and domperidone have on the D2 receptors?
They have a prokinetic effects which promotes gastric emptying
How does histamine cause acid production?
Histamine produce by paracrine cells promote proton pump on the gastric parietal cell to release H+ into the stomach for exchange for K+ into the cells
What drugs serum concentration is reduced if taken at the same time as antacids?
PPI's ACE inhibitors Levothyroxine Some Abx( tetracycline, ciprofloxacin and cephalosporin) Digoxin PPI's
Give two trade name examples of antacids?
Gaviscon
Pepto bismol
Which aminosalicylate has fewer side effects?
Mesalazine has fewer side effects than sulfasalazine
What are the common side effects of aminosalicylates?
GI upset (nausea and dyspesia) and headache
What are the rare but serious blood and renal side effects of aminosalicylate?
Leucopenia and thrombocytopenia
Renal impairement
What affect can sulfasalazine have on mens production of sperm?
oligospermia
Why should you ask specific alarm questions regarding a gastric cancer when prescribing ppi?
It can mask the symptoms of gastric cancer
When should phosphate enemas used cautiously?
Patients with heart failure, ascites and when electrolyte disturbances are present.
Due to significant fluid shift
When should domperidone be used cautiously?
when the patient has cardiac defect as it increase the risk of cardiac incidences
What type of drug is cyclizine?
Anti emetic Histamin H1 receptor antagonist
What is the use of cylcizine?
Treatment of nausea and vomiting caused by motion sickness and vertigo
In who’m should metacolopramide and domperidone be invoved in?
Eldrely, Young adults and children
Any cardiac events
