drugs for constipation Flashcards
what are bulk forming agents?
plant fibre:
psyllium( ispaghula husk), methylcellulose
what is the mechanism of psyllium
indigestible fibres,
absorbs water forming bulk,
emollient gel that distends colon ( increases stool mass)
tht promotes peristalsis.
Adverse effects/ main concerns of bulk forming agents ( psyllium)
bacterial disgestion of plant fibres within the colon can cause flatus, bloating and abdominal pain.
TO AVOID if suspected obstruction.
it interactes with the absorption of other drugs.
Give an example of stool surfactant agents ( stool softeners)
Docusate, mineral oil ( used widely for kids in the past)
MOA of Docusate, stool softener
- lowers surface tension, allowing water and lipids( fats ) to penetrate.
- mineral oil lubricates + retards water absorption from stool
Main concerns for stool softeners
- docusate and mineral oil
mineral oil is not palatable, but may be mixed with fruit juice. ,
- aspiration can result in severe lipid pneumonitis
- long term use can impair absorption of fat soluble vitamins ( A,D,E ,K)
List an example of osmotic laxatives
Non abdorbable sugar/ salts:
lactulose, sodium phosphate,
Balanced Polyethylene Glycol ( PEG)
MOA of osmotic laxatives
lactulose and PEG
-pulls water into faecal mass and create watery stools.
- High doses can produce bowel evacuation within 1-3 hours.
Main concerns of the osmotic laxatives
lactulose and PEG
colonic bacteria act on sugar - causes severe flatus and abdominal cramps.
- important to maintain adequate hydration by increasing oral fluid intake.
- sodium phosphate can cause hyperphosphotaemia, hypernatremia, hypocalcaemia, hypokalemia.
- may cause cardiac arrhythmias, real failure due to tubular deposition of calcium phosphate- nephrocalcinosis.
- should not be used in patients who are frail, elderly on diuretics, unable to maintain adequate hydration, renal insufficiency, cardiac disease.
Main concerns of the osmotic laxatives
lactulose and PEG
colonic bacteria act on sugar - causes severe flatus and abdominal cramps.
- important to maintain adequate hydration by increasing oral fluid intake.
- sodium phosphate can cause hyperphosphotaemia, hypernatremia, hypocalcaemia, hypokalemia.
- may cause cardiac arrhythmias, real failure due to tubular deposition of calcium phosphate- nephrocalcinosis.
- should not be used in patients who are frail, elderly on diuretics, unable to maintain adequate hydration, renal insufficiency, cardiac disease.
which is the safest to use for osmotic laxatives?
PEG.
contains sugar, sodium sulfate, NACL, sodium bicarb, KCL balanced to avoid electrolyte shifts.
does not produce cramps or flatulence.
List an example of stimulant laxatives ( cathartics)
anthraquinone derivatives:
senna
diphenylmethane derivatives:
bisacodyl
how fast does bisacodyl works?
induces bowel movement in 6-10 hours for oral route.
30-60minutes for rectal route. used in conjunction with PEG for colonic cleansing pior to colonoscopy.
MOA of stimulant laxatives
senna bisacodyl
promotes peristalsis by irritating the bowel mucosa. migrating colonic contractions.
how fast does senna take to work?
6-12 hours for PO.
PR is 2 hours.
Main concerns for senna, bisacodyl
- long term use required for neurologically impaired, bed bound.
- chronic use may lead to dependence
- senna: brown pigmentation of colon - melanosis coli
bisacodyl: safe
is phenolphthalein still in use?
no due to cardiac toxicity
List an example of chloride channel activators
Lubiprostone
50% have bowel movement within 24 hours of single dose.
MOA of lubiprostone (CCA)
stimulate type 2 chloride channels in small intestine.
- increasechloride rich fluid secretions
- stimulates motility and shorten intestinal transit time.
Major concerns for CCA lubiprostone
AVOID IN PREGNANCY
after u stop using it, u get constipation again.
Nausea due to delayed gastric emptying (30% of patients)
list an example of opiod receptor antagonist
methylnatrexone bromide
to treat opiod induced constipation in patients receiving palliative care
administered S/C every 2 days.
MOA of opiod receptor antagonist: methylnatrexone bromide
Effects mainly mediated through blockade of intestinal mu (μ) opioid receptors
● Do not readily cross blood-brain barrier so do not block CNS analgesic effects
major concerns of opiod receptor antagonsit methylnatrexone bromide
stomach/ abdominal pain, n/v, diarrhea, flatulence, sweating.
RARE: GI perforation
examples of Serotonin 5-HT4 -Receptor Agonists
Prucalopride
MOA of prucalopride
stimulation of 5 HT4 receptors in GI walls increrases neurotransmitter release and smooth muscle motor activity.
increased smooth muscle activity results in prokinetic effect promoting GI motility.
DO NOT USE IN IO.
adverse effects of 5HT4 receptor antagonist
stomach abdominal pain, nv, dizziness, headache.
severe: prucalopride:
high affinity, nth else.
cisapride: adverse cardiac events
