constipation Flashcards
2 types of constpation
primary/functional
secondary/organic
What must functional constipation include (2 or more of)?
- straining >25%
- lumpy/hard > 25%
- sensation of incomplete evacuation in >25%
- sensation of blockage/obstruction >25%
- manual maneouvres >25%
- < 3 per week
- loose stools rarely present without laxatives
- insufficient criteria for IBS
How long must symptoms have been present for?
criteria fulfilled for 3 months
symptom onset > 6 months
What causes organic constipation?
medication
metabolic diseases
neuropathies
myopathies
When should further investigations take place?
unexplained constipation abdominal pain vomiting blood/mucous straining (tenesmus) long standing unresponsive to treatment
What are the further investigations?
- colonic and anorectal manometry
- stool analysis
- flexible sigmoidoscopy
- colonoscopy
What is 1st line therapy?
non-drug treatment
advice on diet and exercise
What diet and lifestyle advice?
adequate fluid and fiber intake
regular exercise
no tea/coffee (diuretics, can worsen it)
What is given in patients who don’t respond to lifestyle/diet changes?
laxatives
laxatives don’t work
diagnostic testing
main treatment for dyssynergic defecation
biofeedback therapy
When is drug treatment given?
associated with illness
pregnancy
or
poor diet
4 types of laxatives
bulk forming
stimulants
osmotic
faecal softeners
4 examples of bulk forming agents
wheat bran
ispaghula husk
methylcellulose
sterculia
When do bulking agents control fecal consistency?
IBS (diarrhoea)
ileostomy
colostomy
3 MOA of bulk forming agents
- hydrophilic action
- proliferation of colonic bacteria
- degradation of polysaccharides
How does hydrophilic action work in bulking agents?
causes water retention in gut lumen
expands and softens feces
Proliferation of colonic bacteria in bulking agents?
increases fecal bulk
stimulates colonic mucosal receptors
promotes peristalsis
Degradation of polysaccharides in bulking agents?
degradation of polysaccharides in sterculia
to substances that have an osmotic laxative effect
How long do bulking agents take to work?
24hrs
When are bulking agents commonly used?
chronic constipation
diverticular disease
IBS
When to avoid bulking agents?
if colon is atonic
fecal impaction
4 examples of stimulant laxatives
senna
bisacodyl
danthron
sodium picoslfate
2 components in Senna
sennosides A and B
anthrone glycosides
What are sennosides A and B metabolised by gut bacteria to?
rheinanthrone
What does rheinanthrone do?
increases COX 2 expression in macrophage cells
increases prostaglandin E2
PEG2 decreases aquaporin 3 expression in large intestine and epithelial cells
and
stimulates peristalsis
What does a dec in aquaporin 3 cause?
restricts water absorption
increases fecal water content
What is bisacodyl hydrolysed BY?
hydrolysed by intestinal brush border enzymes and colonic bacteria
Active metabolite of bisacodyl
BHPM
How does BHPM work?
directly on colon mucosa
stimulates nerve endings in intestine/rectum walls to produce peristalsis
causes defecation
What is a contact laxative?
increases fluid and salt secretion
onset time for stimulant laxatives?
8-12 hours
when should stimulants be taken
at bed time
stimulant laxatives suppositories onset time
20 - 60 mins
Can stimulant laxatives be used in pregnancy?
no
can cause uterine contraction
chronic use of stimulant laxatives
atonic colon
6 examples of osmotic laxatives
Mg salts lactulose lacitol PEG sodium citrate enemas phosphate enemas
How do osmotic laxatives work?
retain fluid in the colon by osmosis
time onset for phosphate enemas
30 mins
when are phosphate enemas used
prior to surgery or sigmoidoscopy
time onset of lactulose/lacitol (sugars)
up to 48 hours
example of softener
docusate sodium
What is docusate sodium?
a surfactant
How do softeners work?
decrease surface tension and emulsification of fecal matter
allows water to penetrate and mix with stool
softens the stool
When can rectal preparations of softeners not be used?
in haemorrhoids
What drug can be used after 2 failed treatments?
libiprostone
What is lubiprostone?
a bicyclic fatty acid derived from prostaglandin E1
How does lubiprostone work?
activates ClC-2 chloride channel on apical aspect of GI epithelial cells
produces Cl rich fluid secretions
What is lubiprostone used to treat?
chronic idiopathic constipation in adults
tried at least 2 laxatives from different classes at highest tolerated dose
for at least 6 months
failed to provide relief
and
opioid constipation
