B / 25 : Drugs used in constipation and diarrhea. Drugs promoting digestion. Liver and biliary tract

Question 1

Different mechanisms of laxatives (4)

Answer 1

• Bulk forming action on stool
• Stimulant / irritant action on bowel wall
• Softening action
• Lubricating action

Question 2

What is an example of a bulk forming laxative?

Answer 2

Plant fibers

Question 3

What is the mechanism of plant fibers?

Answer 3

They are indigestible, hydrophilic colloids that absorb water and form a gel that distends the colon and increases peristaltic cavity

Question 4

What are 2 osmotic laxatives?

Answer 4

• MgSO4
• Lactulose

Question 5

MOA of MgSO4

Answer 5

Non absorbable salts that retain water in intestines by osmosis : distends the bowel for more movement

Question 6

MOA of lactulose

Answer 6

Metabolized by GI bacteria into lactic acid and acetic acid : decreased pH increases osmotic pressure -> fluid accumulation, colon distention

Question 7

What is a lubricating laxative?

Answer 7

Paraffin oil

Question 8

MOA of paraffin oil

Answer 8

• Lubricates and eases the passage of hard stools
• Should be taken orally in an upright position to avoid aspiration

Question 9

What are 2 stimulant / irritant laxatives?

Answer 9

• Sennoside
• Bisacodyl

Question 10

Sennoside
- MOA
- Indication
- Contraindication
- SE
- Extra

Answer 10

• Degradation product acts directly as IRRITANT on the colonic wall to induce fluid secretion and motility
• Used to empty bowels before surgery
• Can cause miscarriage in pregnant women
• Darkening of stool and urine
• Sennosides occur naturally in plants

Question 11

Bisacodyl
- MOA
- Indication
- SE

Answer 11

• Acts directly on nerve fibers in the colonic mucosa
• For chronic constipation, neurologic bowel dysfunction
• Abdominal cramps

Question 12

When are antidiarrheal agents contraindicated?

Answer 12

In bloody diarrhea

Question 13

What are 3 antidiarrheal agents?

Answer 13

• Diphenoxylate
• Loperamide
• Active charcoal

Question 14

Diphenoxylate, loperamide
- MOA
- Effect
- Extra
- SE

Answer 14

• Synthetic mu opioid Agonists
• Activate mu opioid receptors in the ENS and inhibit Ach release, which decreases motility
• Diphenoxylate is used with atropine to decrease liability, but loperamide is used alone
• Abdominal cramps, CNS effects

Question 15

MOA of active charcoal

Answer 15

Attract and expel ingested toxins from GI

Question 16

Types of bile salts

Answer 16

• Primary bile salts : formed in liver by cholesterol
• Secondary bile salts : produced by the gut microbiota

Question 17

What do bile salts do?

Answer 17

They emulsify dietary fats and the cholesterol of bile : if the bile salt concentration of bile is low, then cholesterol may precipitate and form gallstones

Question 18

Drugs that act on the liver and biliary tract

Answer 18

• Ursodeoxycholic acid
• Acetylcysteine
• Silymarin

Question 19

Ursodeoxycholic acid
- MOA
- Effect
- Indication
- Contraindication
- SE

Answer 19

• Decreases cholesterol content of bile by decreasing hepatic cholesterol secretion
• Inhibits formation of gallstones
• For cholelithiasis, primary bile cirrhosis, promotion of digestion
• NOT if : acute hepatitis, biliary obstruction
• Diarrhea

Urso : bear - acid : pool of acid / rock : prevents down gallstones

Question 20

Acetylcysteine
- MOA
- Effect

Answer 20

• Hepatoprotective agent, antidote for paracetamol’s toxic metabolite
• Increases production of depleted antioxidant glutathione + mucolytic effect (asthma + COPD)

Question 21

Silymarin
- MOA
- Effect
- Indication

Answer 21

• Hepatoprotective agent
• Decrease uptake of amatoxin into heptic cells + antioxidant effect + inhibition of lipid peroxidation
• For amanita poisoning and liver injury caused by alcohol, acetaminophen