Laxatives

Question 1

Classify laxatives according to mechanism of action

Answer 1

1. Bulk laxatives (dietary fibre)
2. stimulant or irritant laxatives
3. stool softeners
4. 5HT4 agonist
5. PG analogue

Question 2

What is the mechanism of action of bulk forming laxatives

Answer 2

They’re indigestible and they absorb water, swell up and increase the bulk of stool. This causes mechanical distension and stimulates peristalsis and promotes defaecation

Question 3

Name Bulk forming laxatives

Answer 3

1. Agar
2. Methylcellulose
3. bran
4. ispaghula

Question 4

Bulk forming laxatives should be avoided in which conditions

Answer 4

Magacolon or megarectum

Question 5

Name stool softeners

Answer 5

1. Docusates (docusate salts including diacetyl sodium sulphosuccinate and diacetyl calcium sulphosuccinate)
2. Liquid paraffin

Question 6

What are the adverse effects of liquid paraffin

Answer 6

1. Lipid pneumonia if the drug enters the lungs
2. Long-term news can cause malabsorption of vitamin A, D, E and K (fat soluble vitamins)
3. Leakage of faecal matter through the anal sphincter

Question 7

Which drug is contraindicated in pregnancy as it may cause reflex stimulation of uterus

Answer 7

Stimulant laxatives

Question 8

Name the mechanism of action of stimulant/irritant laxatives

Answer 8

They have a direct action on enteric neurons and GI mucosa by increasing prostaglandin and cAMP levels but inhibiting Na+ and K + ATPase activity

Question 9

Chronic use of stimulus/irritant laxatives leads to what

Answer 9

Atonic colon 

Question 10

Name stimulant/irritant laxatives

Answer 10

1. sodium picosulphate
2. bisacodyl
3. Phenolphthalein
4. Anthra quinone derivatives (senna and cascara)

Question 11

Which drug should be avoided in lactating mothers and why

Answer 11

Anthraquinone Derivatives (senna and cascara)
Because the drug is a secreted in milk

Question 12

What are the side effects of Anthra quinone

Answer 12

1. Skin rashes
2. black pigmentation of the colonic mucosa
3. discolouration of urine
4. can cause colonic atony

Question 13

Name 5 HT4 agonist

Answer 13

Prucalopride

Question 14

Name PG analogue used as a laxative

Answer 14

Lubiprostone

Question 15

Name is osmotic Laxatives

Answer 15

1. Magnesium sulphate
2. magnesium hydroxide
3. sodium sulphate
4. sodium phosphate
5. lactulose
6. polyethylene glycol

Question 16

Osmotic laxatives Are contraindicated in which patients and why

Answer 16

Young children and patients with renal failure
because they may cause CNS or cardiac depression

Question 17

Which drug is used in hepatic coma to reduce blood ammonia levels

Answer 17

Lactulose

Question 18

What are the uses of laxatives

Answer 18

1. Acute functional constipation (bull laxatives)
2. to prevent straining during defaecation in patients with cardiovascular disease, eye surgery, hernia etc. (docusates or Bulk lax)
3. in patients with hepatic coma to reduce blood ammonia levels (lactulose)
4. preoperatively in bowel surgery, colonoscopy and abdominal x-ray (osmotic lax or bisacodyl)
5. following anti-helminitics (saline lax)
6. drug poisoning (saline lax)
7. treat constipation in children and pregnant women. (Lactulose)