drugs for constipation

Question 1

what are bulk forming agents?

Answer 1

plant fibre:

psyllium( ispaghula husk), methylcellulose

Question 2

what is the mechanism of psyllium

Answer 2

indigestible fibres,
absorbs water forming bulk,
emollient gel that distends colon ( increases stool mass)
tht promotes peristalsis.

Question 3

Adverse effects/ main concerns of bulk forming agents ( psyllium)

Answer 3

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.

Question 4

Give an example of stool surfactant agents ( stool softeners)

Answer 4

Docusate, mineral oil ( used widely for kids in the past)

Question 5

MOA of Docusate, stool softener

Answer 5

• lowers surface tension, allowing water and lipids( fats ) to penetrate.
• mineral oil lubricates + retards water absorption from stool

Question 6

Main concerns for stool softeners

• docusate and mineral oil

Answer 6

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)

Question 7

List an example of osmotic laxatives

Answer 7

Non abdorbable sugar/ salts:
lactulose, sodium phosphate,

Balanced Polyethylene Glycol ( PEG)

Question 8

MOA of osmotic laxatives
lactulose and PEG

Answer 8

-pulls water into faecal mass and create watery stools.

• High doses can produce bowel evacuation within 1-3 hours.

Question 9

Main concerns of the osmotic laxatives

lactulose and PEG

Answer 9

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.

Question 10

Main concerns of the osmotic laxatives

lactulose and PEG

Answer 10

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.

Question 11

which is the safest to use for osmotic laxatives?

Answer 11

PEG.

contains sugar, sodium sulfate, NACL, sodium bicarb, KCL balanced to avoid electrolyte shifts.

does not produce cramps or flatulence.

Question 12

List an example of stimulant laxatives ( cathartics)

Answer 12

anthraquinone derivatives:
senna
diphenylmethane derivatives:
bisacodyl

Question 13

how fast does bisacodyl works?

Answer 13

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.

Question 14

MOA of stimulant laxatives
senna bisacodyl

Answer 14

promotes peristalsis by irritating the bowel mucosa. migrating colonic contractions.

Question 15

how fast does senna take to work?

Answer 15

6-12 hours for PO.
PR is 2 hours.

Question 16

Main concerns for senna, bisacodyl

Answer 16

• long term use required for neurologically impaired, bed bound.
• chronic use may lead to dependence
• senna: brown pigmentation of colon - melanosis coli

bisacodyl: safe

Question 17

is phenolphthalein still in use?

Answer 17

no due to cardiac toxicity

Question 18

List an example of chloride channel activators

Answer 18

Lubiprostone
50% have bowel movement within 24 hours of single dose.

Question 19

MOA of lubiprostone (CCA)

Answer 19

stimulate type 2 chloride channels in small intestine.
- increasechloride rich fluid secretions
- stimulates motility and shorten intestinal transit time.

Question 20

Major concerns for CCA lubiprostone

Answer 20

AVOID IN PREGNANCY
after u stop using it, u get constipation again.
Nausea due to delayed gastric emptying (30% of patients)

Question 21

list an example of opiod receptor antagonist

Answer 21

methylnatrexone bromide

to treat opiod induced constipation in patients receiving palliative care

administered S/C every 2 days.

Question 22

MOA of opiod receptor antagonist: methylnatrexone bromide

Answer 22

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

Question 23

major concerns of opiod receptor antagonsit methylnatrexone bromide

Answer 23

stomach/ abdominal pain, n/v, diarrhea, flatulence, sweating.

RARE: GI perforation

Question 24

examples of Serotonin 5-HT4 -Receptor Agonists

Answer 24

Prucalopride

Question 25

MOA of prucalopride

Answer 25

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.

Question 26

adverse effects of 5HT4 receptor antagonist

Answer 26

stomach abdominal pain, nv, dizziness, headache.

severe: prucalopride:
high affinity, nth else.

cisapride: adverse cardiac events