Antimuscarinics, CV and GI

Question 1

Give the 3 main clinical indications for the use of cardiovascular and gastrointestinal antimuscarinics.

Answer 1

1) Atropine for first line management of severe or symptomatic bradycardia to increase HR.
2) Antimuscarinics such as hyoscine butyl bromide are first line pharmacological Rx for IBS, where they are used for their antispasmodic effect.
3) In palliative care they are used to reduce copious respiratory secretions (hyoscine butylbromide).

Question 2

1) Give the basic mechanism of action of antimuscarinics.

2) What does stimulation of the muscarinic receptor normally cause?

Answer 2

1) Competitive inhibitor of acetylcholine.

2) Parasympathetic ‘rest and digest’ effects.

Question 3

1) What does antagonism of the muscarinic receptor cause?

Answer 3

1) increase HR and conduction, reduce smooth muscle tone, reduce peristaltic contraction, reduce secretions in gut and respiratory tract.

Question 4

1) What effects do antimuscarinics have in the eye?

Answer 4

1) Relaxation of pupillary constrictor and ciliary muscles, leading to pupillary dilation and prevention of accommodation.

Question 5

1) Give 3 systemic side effects of antimuscarinics.
2) Give 2 CNS side effects of antimuscarinics.
3) Give an ocular side effect of antimuscarinics.
4) How do antimuscarinics cause urinary retention in patients with BPH?

Answer 5

1) Tachycardia, dry mouth, constipation.
2) Drowsiness and confusion (particularly in elderly).
3) Blurred vision.
4) They can potentially reduce detrusor muscle activity.

Question 6

1) Which type of patients should antimuscarinics be use with caution in? Why is this?
2) In which groups of patients should antimuscarinics be avoided? What is the exception?

Answer 6

1) Those with angle-closure glaucoma as they can precipitate a dangerous rise in intraocular pressure.
2) Those with or at risk of arrhythmias, unless the indication for use is bradycardia.

Question 7

When are the adverse effects of antimuscarinics more pronounced?

Answer 7

When combined with other drugs that have antimuscarinic effects such as tricyclic antidepressants.

Question 8

1) What drug is usually given for bradycardia?

2) What other drug might be used for bradycardia? What are the advantages and disadvantages?

Answer 8

1) Atropine IV in incremental doses.

2) Glycopyrronium - causes less drowsiness but not normally readily available on wards.

Question 9

Which drugs might be given to control respiratory secretions and how are they administered?

Answer 9

Hyoscine butyl bromide/ hyoscine hydrobromide subcutaneously by injection or continuous subcut. infusion.

Question 10

Why is it recommended that a first dose of atropine for bradycardia treatment should be no less than 600mcg?

Answer 10

Because paradoxically, low doses of atropine can transiently slow the heart rate before the desired chronotropic effect begins.

Question 11

Name 2 other antispasmodic agents which might be used for IBS.

Answer 11

Mebeverine and Peppermint oil