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drugs affecting motility Flashcards

1
Q

what stimulates parietal cells to secrete acid?

A

histamine, proteins, gastrin, ACH ( after stomach stretching and sight/smell of food)

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2
Q

name 3 types of drugs that affect acid secretion and 2 examples of drugs from those categories

A

antacids - calcium carbonate, sodium bicarbonate, MgOH, AlOH
H2 receptor antagonist - ranitidine and cimetidine
Proton pump inhibitors - omeprazole and lansoprazole

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3
Q

how do antacids work?

A

neutralise stomach acid

relieve occasion gastritis and heart burn

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4
Q

what chemical is Rennie?

A

CaCO3

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5
Q

what chemical is gaviscon?

A

NaHCO3 or CaCO3

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6
Q

what are the side effects of antacids?

A

AlOH can cause constipation
MgOH can cause osmotic diarrhoea
CaCO3 - excess Ca
NaHCO3 - excess Na

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7
Q

how do ranitidine and cimetidine work? what is the issue with this mechanism?

A

block H2 receptors to prevent histamine being released and thus reduced stimulation to acid secretion.

  1. there are other methods of acid secretion e.g. ACH
  2. after time the H2 receptors become down regulated and there is tolerance to these medications.
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8
Q

how does the speed of onset of H2 antagonists and PPIs differ?

A

H2 receptor blockers quick onset, short acting

PPI - slow onset but last longer

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9
Q

what are the side effects of cimetidine? ranitidine?

A

both: rash, fatigue and dizziness (think histamine)
cimetidine - N, V, D and sometimes gynacomastia
cimetidine also interfers with CYP450 and thus warfarin levels increase

ranitidine is stronger and less side effects so preferred

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10
Q

when are PPIs used?

A

more severe acid problems - peptic ulcer, zollinger Ellison syndrome

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11
Q

how do PPIs work?

A

covalently bind H/K ATPase and target it for irreversible destruction.
these drugs are activated by acid

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12
Q

what are the side effects of PPIs?

A

diarrhoea, nausea
increased risk of GI infections
anaemia - intrinsic factor
risk of gastric atrophy with prolonged use
recently shown to have a link with gastric cancer

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13
Q

when should omeprazole be avoided?

A

people taking phenytoin or warfarin because it inhibits CYP450

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14
Q

how does treatment of acid secretion differ in hospitals compared to GP setting?

A

GP: step up i.e. try antacids then H2 then PPIs

hospital= step down as symptoms get better.

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15
Q

other than drug therapy what other advice can be given to someone complaining of acid reflux?

A

drink milk and avoid citric foods
don’t eat before bed and sleep with a pillow
no NSAIDS, no alcohol

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16
Q

describe the underlying mechanism behind gut motility.

A

interstitial cells of cajal act as pacemakers to drive depolarisation which spreads through gap junctions of muscles giving intrinsic rhythmic contraction.
this is modulated by extrinsic factors:
parasympathetic innervation –> ACH –> increased gut motility
sympathetic –> NA –> reduced gut motility
motillin released from duodenum causes increased motility
myotonic activity - stretch of bowel wall stimulates contractions

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17
Q

does ondansetron target nausea or vomiting more?

A

vomiting

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18
Q

How does a change in bowel motility lead to constipation/diarrhoea?

A

increased motility –> diarrhoea

reduced motility –> constipation

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19
Q

what are the uses of laxative?

A

relieve constipation
clear bowel before medical proceedures
good for liver failure to treat encephalopathy

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20
Q

name 4 different groups of laxitive

A

bulk laxative
osmotic laxatives
stool softeners
stimulant laxatives

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21
Q

give examples of bulk laxitives

A

isphaghula
fibrogel
bran
methylcellulose

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22
Q

describe how bulk laxatives work

A

Adds more undigestible material to the bowel such that water is drawn in to bulk faeces. this stretches the bowel wall and stimulates peristalsis

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23
Q

how are bulk laxatives given?

A

orally

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24
Q

when are bulk laxatives indicated and when are they contraindicated?

A

indicated when stools are hard e.g. IBS, pregnancy

contraindicated in dysphagia, bowel obstruction, faecal compaction, colonic atony

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25
Q

what are the side effects of bulk laxatives?

A

abdominal distention, flatulence, GI obstruction

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26
Q

what advice would you give someone taking bulk laxatives?

A

need to have a good water intake

may take few days to work

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27
Q

give examples of osmotic laxatives? How are each administered?

A

lactulose - oral
movicol - oral
sodium salts and mg salts = phosphate enemas

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28
Q

when are osmotic laxatives indicated?

A

constipation
lactulose is indicated in hepatic failure (remove NH4 from bowel)
phosphate enemas are good for resistant constipation and bowel prep before surgery.

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29
Q

what are the side effects of osmotic laxatives?

A

cramps, flatulence and abdo pain

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30
Q

how quickly do osmotic laxatives work?

A

lactulose - 48hours
movicol 2-4 days
phosphate enemas - very quickly so good if severe constipation needs to be relieved quickly

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31
Q

when are osmotic laxatives contraindicated?

A

bowel obstruction

32
Q

how do osmotic laxatives work?

A

e.g. lactulose

disaccharide that cant be digested/absorbed so instead broken down by intestinal bacteria into lactic acid and acetic acid. This draws water into the bowel. stretches colon –> peristalsis

33
Q

name 2 faecal softeners ( how are they given)

A

glycerol - suppository

arachis oil - enema

34
Q

when are faecal softeners indicated?

A

constipation , faecal compaction

anal fissure, haemarroids

35
Q

when are faecal softeners contraindicated?

A

<3yrs

36
Q

are faecal softeners quick or short acting?

A

slow but safe

37
Q

how do faecal softeners work?

A

lubricates and softens stool

38
Q

name different stimulant /irritant laxatives

A

Senna
bisacodyl
sodium picosulphate
danthron

39
Q

how are stimulant laxatives given? how quickly do they work?

A

orally

6-8 hours - so adviced to take at night

40
Q

how do stimulant laxatives work?

A

stimulate/irritate the nerve receptors (stretch receptors) of the bowel wall to result in increased peristalsis and electrolye/water secretions into the bowel.

41
Q

when are stimulant laxatives indicated and contraindicated?

A

indicated in constipation, also to clear bowel for surgery etc.
contraindicated in intestinal obstruction

42
Q

what are the side effects of stimulant laxatives

A

the stretch receptors can become unresponsive leading to colonic atony - bowel lacks tone if used repeatedly (Melanosis coli)
Also electrolyte imbalances from fluid shifts can result in hypokalaemia and ileus

overall can worsen constipation

43
Q

other than laxatives how else can we help someone with constipation?

A

try to find cause of constipation and relieve it
e.g. stop codeine , verapamil, diuretics, anti-depressants (if possible)

treat any parkinsons, cancer, hypothyroid

increase exercise, water intake, reduce stress
advice on diet

44
Q

name 3 groups of anti-diarrhoeal drugs

A

bulking agents
anti-motility drugs
fluid adsorbants

45
Q

name 2 different antimotility drugs. How do they differ?

A 
codeine phosphate (an opioid)
loperamide (immodium) - this is an opioid analog that is more potent than opioids and does not penetrate CNS
46
Q

how do anti-diarrhoeal drugs work?

A

act on U receptors in the bowel to reduce colonic motility, increase anal tone and reduce the sensory defaecation reflex

47
Q

when are anti-motility drugs used and when are they contraindicated?

A

used for chronic diarrhoea

not for IBS/D - precipitate toxic megacolon

48
Q

what are the side effects of anti-motility drugs?

A

N&V
abdo cramps
constipation
drowsiness

49
Q

how do bulking agents work to treat diarrhoea?

A

add non-digestable insoluble content to the bowel that will absorb watery diarrhoea and thicken faeces

50
Q

when are bulking agents good in diarrhoea?

A

IBS or ileostomy

51
Q

name an fluid adsorbant that can be used to treat diarrhoea

A

Kaolin

52
Q

name a drug used to treat IBS and explain what it does.

A

mebeverine

reduces colonic activity to reduce intestinal muscle spasms. works as an anti-cholinergic

53
Q

what are the side effects of mebeverine?

A

constipation
allergy
headaches, dizziness
(does not have anti-cholinergic effects)

54
Q

describe the physiology behind vomitting

A

the vomiting centre is part of the medulla oblongata - a region called the postrema (which lies at the floor of the 4th ventricle) it is called the chemoreceptor trigger zone.
this area receives inputs from:
- vestibular system –> medulla
- taste, smell, pain, anxiety –> cortex –> medulla
- directly by drugs, uraemia and opioids
- raised ICP –> meulla
these inputs combine to initiate vomiting.

NT involved = ACh, dopamine, serotonin, histamine and substance P

vomiting results in closure of pyloric sphincter, relaxation of cardia and oesophagus whilst the abdo wall and diaphragm contract to expel food out.

55
Q

before treating N&V with anti-emetics what should you also consider?

A

the cause and try treat the cause

e.g. if it is anxiety - benzodiazepines may help

56
Q

name 6 classes of anti-emetics

A 
dopamine receptor antagonists
serotonin receptor antagonist
histamine receptor antagonists
anti-muscarnics 
butyrophenones
steroids
57
Q

name 2 examples of dopamine receptor antagonists. what routes can they be given?

A

metoclopramide - IM, IV, oral

domperidone - oral and rectal

58
Q

how do dopamine receptor antagonists work (anti-emetics)

A

inhibit signalling within postrema
inhibit dopamine receptors in stomach to increase gastric emptying
also have anti-cholinergic effects to inhibit vagal afferents

59
Q

what are the side effects of metoclopramide (when should it be avoided)

A

reduced dopamine:

- galactorrhoea (increased prolactin)
- (extrapyramidal effect): dyskinesia and dystonia - avoid in parkinsons

dizziness, diarrhoea, xerostomia

60
Q

name a serotonin receptor antagonist (antiemetics) how is it given?

A

ondansetron
oral, IV, IM
8 hourly

61
Q

when is ondansetron good to use?

A

post radiation sickness, after chemotherapy, after surgery, food poisoning

62
Q

how does ondansetron work?

A

inhibits signalling within postrema

reduces 5HT action within the gut (which normally stimulates vagal afferents to signal to postrema)

63
Q

what are the ADRs of ondansetron?

A

headache
flushing
constipation

can be enhanced by steroids to give tachycardia and confusion

64
Q

in surgical patients when is ondansetron given?

A

towards the end of surgery

65
Q

name an anti-muscarinic used as an anti-emetic and how does this work?

A

hyoscine
anti-spasmodic and antisecretory
given orally or transdermal patch

66
Q

when I hyoscine mainly indicated?

A

travel sickness

67
Q

what are the ADRs of hyoscine?

A

tachycardia
blurred vision
urine retention
dry mouth

68
Q

name a H1 receptor antagonist. how is it given. how does it work?

A

cyclizine (also promethazine - good for morning sickness)
oral, IV, IM (up to 6hrly)
blocks H1 in medulla

69
Q

when is cyclizine good to use? when is it contraindicated?

A

acute N&V

contraindicated in MI

70
Q

what are the side effects of cyclizine?

A

crosses BBB - sedative
prolongs QT, tachycardia
xerostomia

71
Q

why is ondansetron often good for day surgery cases? what anti-emetic is less useful and why?

A

not associated with drowsiness, extrapyramidal effects or long recovery from anaesthesia

cyclizine is less useful for day surgery because of sedative effects

72
Q

what steroid is used for N&V and when is it given?

A

dexamethasone IV
can be given before induction of anaesthesia
unclear mechanism

also good for N&V due to chemo and raised ICP (brain tumours)

73
Q

what side effects do steroids have, when treating N&V?

A

mood changer, blurred vision , fast HR

74
Q

what are butyrophenones?

A

anti-emetics
include haloperidol and droperidol
antagonise dopamine and a adrenergic receptors

75
Q

what side effects are experienced with haloperidol (butyrophenones)?

A

vasodilation/hypotension
increase QT
sedation
nightmares

76
Q

what is cyclimorph?

A

cyclizine and morohine

77
Q

what drug can be used to treat dystonia in those taking dopamine antagonists?

A

procyclidine

Surgery sara (10 decks)

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