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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
what are the side effects of bulk laxatives?
abdominal distention, flatulence, GI obstruction
26
what advice would you give someone taking bulk laxatives?
need to have a good water intake | may take few days to work
27
give examples of osmotic laxatives? How are each administered?
lactulose - oral movicol - oral sodium salts and mg salts = phosphate enemas
28
when are osmotic laxatives indicated?
constipation lactulose is indicated in hepatic failure (remove NH4 from bowel) phosphate enemas are good for resistant constipation and bowel prep before surgery.
29
what are the side effects of osmotic laxatives?
cramps, flatulence and abdo pain
30
how quickly do osmotic laxatives work?
lactulose - 48hours movicol 2-4 days phosphate enemas - very quickly so good if severe constipation needs to be relieved quickly
31
when are osmotic laxatives contraindicated?
bowel obstruction
32
how do osmotic laxatives work?
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
name 2 faecal softeners ( how are they given)
glycerol - suppository | arachis oil - enema
34
when are faecal softeners indicated?
constipation , faecal compaction | anal fissure, haemarroids
35
when are faecal softeners contraindicated?
<3yrs
36
are faecal softeners quick or short acting?
slow but safe
37
how do faecal softeners work?
lubricates and softens stool
38
name different stimulant /irritant laxatives
Senna bisacodyl sodium picosulphate danthron
39
how are stimulant laxatives given? how quickly do they work?
orally | 6-8 hours - so adviced to take at night
40
how do stimulant laxatives work?
stimulate/irritate the nerve receptors (stretch receptors) of the bowel wall to result in increased peristalsis and electrolye/water secretions into the bowel.
41
when are stimulant laxatives indicated and contraindicated?
indicated in constipation, also to clear bowel for surgery etc. contraindicated in intestinal obstruction
42
what are the side effects of stimulant laxatives
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
other than laxatives how else can we help someone with constipation?
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
name 3 groups of anti-diarrhoeal drugs
bulking agents anti-motility drugs fluid adsorbants
45
name 2 different antimotility drugs. How do they differ?
``` codeine phosphate (an opioid) loperamide (immodium) - this is an opioid analog that is more potent than opioids and does not penetrate CNS ```
46
how do anti-diarrhoeal drugs work?
act on U receptors in the bowel to reduce colonic motility, increase anal tone and reduce the sensory defaecation reflex
47
when are anti-motility drugs used and when are they contraindicated?
used for chronic diarrhoea | not for IBS/D - precipitate toxic megacolon
48
what are the side effects of anti-motility drugs?
N&V abdo cramps constipation drowsiness
49
how do bulking agents work to treat diarrhoea?
add non-digestable insoluble content to the bowel that will absorb watery diarrhoea and thicken faeces
50
when are bulking agents good in diarrhoea?
IBS or ileostomy
51
name an fluid adsorbant that can be used to treat diarrhoea
Kaolin
52
name a drug used to treat IBS and explain what it does.
mebeverine | reduces colonic activity to reduce intestinal muscle spasms. works as an anti-cholinergic
53
what are the side effects of mebeverine?
constipation allergy headaches, dizziness (does not have anti-cholinergic effects)
54
describe the physiology behind vomitting
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
before treating N&V with anti-emetics what should you also consider?
the cause and try treat the cause | e.g. if it is anxiety - benzodiazepines may help
56
name 6 classes of anti-emetics
``` dopamine receptor antagonists serotonin receptor antagonist histamine receptor antagonists anti-muscarnics butyrophenones steroids ```
57
name 2 examples of dopamine receptor antagonists. what routes can they be given?
metoclopramide - IM, IV, oral | domperidone - oral and rectal
58
how do dopamine receptor antagonists work (anti-emetics)
inhibit signalling within postrema inhibit dopamine receptors in stomach to increase gastric emptying also have anti-cholinergic effects to inhibit vagal afferents
59
what are the side effects of metoclopramide (when should it be avoided)
reduced dopamine: - galactorrhoea (increased prolactin) - (extrapyramidal effect): dyskinesia and dystonia - avoid in parkinsons dizziness, diarrhoea, xerostomia
60
name a serotonin receptor antagonist (antiemetics) how is it given?
ondansetron oral, IV, IM 8 hourly
61
when is ondansetron good to use?
post radiation sickness, after chemotherapy, after surgery, food poisoning
62
how does ondansetron work?
inhibits signalling within postrema | reduces 5HT action within the gut (which normally stimulates vagal afferents to signal to postrema)
63
what are the ADRs of ondansetron?
headache flushing constipation can be enhanced by steroids to give tachycardia and confusion
64
in surgical patients when is ondansetron given?
towards the end of surgery
65
name an anti-muscarinic used as an anti-emetic and how does this work?
hyoscine anti-spasmodic and antisecretory given orally or transdermal patch
66
when I hyoscine mainly indicated?
travel sickness
67
what are the ADRs of hyoscine?
tachycardia blurred vision urine retention dry mouth
68
name a H1 receptor antagonist. how is it given. how does it work?
cyclizine (also promethazine - good for morning sickness) oral, IV, IM (up to 6hrly) blocks H1 in medulla
69
when is cyclizine good to use? when is it contraindicated?
acute N&V | contraindicated in MI
70
what are the side effects of cyclizine?
crosses BBB - sedative prolongs QT, tachycardia xerostomia
71
why is ondansetron often good for day surgery cases? what anti-emetic is less useful and why?
not associated with drowsiness, extrapyramidal effects or long recovery from anaesthesia cyclizine is less useful for day surgery because of sedative effects
72
what steroid is used for N&V and when is it given?
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
what side effects do steroids have, when treating N&V?
mood changer, blurred vision , fast HR
74
what are butyrophenones?
anti-emetics include haloperidol and droperidol antagonise dopamine and a adrenergic receptors
75
what side effects are experienced with haloperidol (butyrophenones)?
vasodilation/hypotension increase QT sedation nightmares
76
what is cyclimorph?
cyclizine and morohine
77
what drug can be used to treat dystonia in those taking dopamine antagonists?
procyclidine

Surgery sara (10 decks)

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