Antimotility drugs

Question 1

Give the main clinical indication for the use of anti-motility drugs.

Answer 1

Symptomatic treatment for diarrhoea, usually in the context of irritable bowel syndrome or viral gastroenteritis.

Question 2

1) Give an example of an anti-motility drug.

2) How is Loperamide similar and different to Pethidine?

Answer 2

1) Loperamide
2) It is an opioid which is pharmacologically similar to pethidine but does not penetrate the CNS so has no analgesic effects.

Question 3

Describe the basic mechanism of action of anti motility drugs such as Loperamide.

Answer 3

Mu opioid receptor agonist in GI tract > increases non-propulsive contractions of the gut smooth muscle but reduces peristaltic contractions > transit of bowel contents is slowed > anal sphincter tone is increased.

Question 4

What does slower gut transit allow and how is this beneficial?

Answer 4

Allows more time for water absorption which has a desirable effect in hardening the stool.

Question 5

1) Apart from loperamide give the other class of drugs which might be useful as anti-motility drugs.
2) Why might you use these other drugs over Loperamide?

Answer 5

1) Other opioids (such as Codeine phosphate).

2) If a patient also needs analgesia.

Question 6

1) Give 3 predictable adverse effects of Loperamide.
2) What are 2 risks when CNS penetrating opioids are used for diarrhoea?
3) Through what mechanism might indirect adverse effects arise as a result of anti-motility drugs?

Answer 6

1) Constipation, flatulence, abdominal cramping.
2) Opioid toxicity and dependance.
3) Inappropriate inhibition of peristalsis.

Question 7

1) When and why should use of Loperamide be avoided?
2) Why should Loperamide not be used in acute bloody diarrhoea?
3) Use of anti-motility drugs increases the risk of haemolytic-uraemia-syndrome which is associated with what?

Answer 7

1) Acute ulcerative colitis/ C. Diff colitis: where inhibition of peristalsis increases risk of toxic megacolon and bowel perforation.
2) Because this may signify a bacterial infection.
3) Certain strains of E. Coli.

Question 8

1) Why is it unwise to prescribe an anti-motility drug for patients who develop diarrhoea while in hospital?
2) When might you be able to prescribe anti-motility drugs in a hospital setting?

Answer 8

1) Because of the risk of C. difficile infection.

2) After a positive viral PCR screen or negative C. difficile toxin test.