Bradycardia

Question 1

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Common indications

Answer 1

1. Atropine is used first-line in the management of severe or symptomatic bradycardia to increase HR
2. Antimuscarinics (particularly hyoscine butylbromide) are a first-line pharmacological treatment for IBS where there used for antispasmodic effect
3. In the care of dying patient, antimuscarinics (e.g. hyoscine) may have a role in reducing copious respiratory secretions

Question 2

Antimuscarinics (atropine, hyoscine, glycopyrronium)

MOA

Answer 2

• Antimuscarinic drugs bind to there muscarinic receptors, where they act as a competitive inhibitor of ACh
• Stimulation of the muscarinic receptor brings about a wide range of parasympathetic rest and digest effects.
• Blocking the receptor, antimuscarinics have the opposite effects: they increase HR and conduction; reduce smooth muscle tone and peristaltic contraction, including in the gut and urinary tract. Reducing secretions in respiratory and gut
• In the eye they cause relaxation of the pupillary constrictor and ciliary muscles, causing pupillary dilation and preventing accomodation

Question 3

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Important adverse effects

Answer 3

• Predictably from their antagonism of parasympathetic rest and digest effects, antimuscarinics can cause tachycardia, dry mouth and constipation
• By reducing detrusor muscle activity, they can cause urinary retention and in patients with benign prostatic hypertrophy
• The ocular effects may cause blurred vision, especially for near objects
• Some antimuscarinics (including atropine) have central effects, which may precipitate drowsiness and confusion, particularly in the elderly

Question 4

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Warnings

Answer 4

• Antimuscarinics should be used with caution in patients susceptible to angle-closure glaucoma, in whom they can precipitate a dangerous rise in intraocular pressure
• They should generally be avoided in patients at risk of arrhythmias (e.g. those with significant cardiac disease), unless the indication for use is bradycardia

Question 5

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Important interaction

Answer 5

• Adverse effects are more pronounced when they are combined with other drugs that have antimuscarinics effects, such as tricyclic antidepressants

Question 6

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Prescription

Answer 6

• For Bradycardia, atropine is usually preferred and is given IV in incremental doses (e.g. 300-600 mcg every 1-2 mins) until an acceptable HR is restored
• Glycopyrronium is an alternative, it does not penetrate that brain so causes drowsiness, but it tends not to be readily available on wards
• For IBS, an antimuscarinic is taken orally on a regular basis: hyoscine 10mg 8hrly is a common choice. This is available OTC
• For the control of respiratory secretions, hyoscine is usually given SC, either by injection or as part of a continuous SC infusion
• NB0 that hyoscine hydrobromide and butylbromide have very differnt dosing

Question 7

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Communication

Answer 7

• Depending on the clinical context, it may be appropriate to warn patients about common adverse effects of antimuscarinics, such as dry mouth and blurred vision

Question 8

Antimuscarinics (atropine, hyoscine, glycopyrronium)

Monitoring

Answer 8

• When using antimuscarinics to increase HR, high-intensity monitoring (including continuous cardiac rhythm monitoring) is required
• It is essential that this is continued after restoration of normal HR, as the effect of the drug may only be transient
• For other indications enquiry about symptoms is the best form of monitoring
• The dose is titrated to achieve the optimal balance between beneficial and adverse effects