Laxatives

Question 1

What are some examples of laxatives

Answer 1

• Softeners = Lactulose
• Stimulants = Senna
• Bulking agent = ispaghula husk

Question 2

What are the indications for using laxatives

Answer 2

• Constipation + faecal impaction

- hepatic encephalopathy + surgical bowel prep (osmotic)

Question 3

What is the mechanism of action for laxatives

Answer 3

Bulk forming
- Hydrophilic substance (e.g. cellulose) attracts water into stool + ^ stool bulk stimulates peristalsis

Osmotic

• osmotically active substances (sugar/alcohol) which remain in lumen (not absorbed). Hold water in stool –> stim peristalsis
• Lactulose reduced ammonia absorption –> good for hepatic encephalopathy

Stimulant

• IRRITANT/CONTACT
• ^ H20 + electrolytes secretion from mucosa –> ^ vol colonic content –> stim peristalsis

Question 4

What are the side effects of laxatives

Answer 4

• diarrhoea
• abdo cramps, flatulence

Rarely
- Hypokalaemia, colonic atony

Question 5

What are some contra-indications

Answer 5

• bowel obstruction
• bowel inflam (UC/crohns)
• Diabetes (senna coated in sugar)
• rectal preparations avoided if haemorrhoids
• osmotic can cause significant fluid shift –> careful in HF, ascites

Question 6

What are some interactions

Answer 6

• Digoxin (hypokalaemic causes toxicity)
• Furosemide and Thiazides (hypokalaemia)
• Warfarin (GI bleeds)