IBS

Question 1

Antimuscarinics- CV and GI uses

Common indications

Answer 1

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

Question 2

Antimuscarinics- CV and GI uses

MOA

Answer 2

• Antimuscarinics drugs bind to the muscarinic receptor, where they act as a competative inhibitor of ACh
• Stimulation of the muscarinic receptor brings about a wide range of parasympathetic rest and digest effects
• In blocking the receptor, antimuscarinics have the opposite effects: they increase HR and conduction; reduce smooth muscle tone and peristaltic contraction, including gut and UT
• Reduce secretions from glands in the respiratory tract and gut
• In the eye they cause relaxation of the pupillary constrictor and cillilary muscles, causing pupillary dilation and preventing accomodation respectively

Question 3

Antimuscarinics- CV and GI uses

Adverse effects

Answer 3

• Predictably from their antagonism of parasympathetic rest and digest effects, antimuscarinics can cause tachycarida, dry mouth and constipation
• By reducing detrusor muscle activity, the can cause urinary retention 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- CV and GI uses

Warnings

Answer 4

• Antimuscarinics should be used with caution in patients suspectible 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 unless the indication for use is bradycardia

Question 5

Antimuscarinics- CV and GI uses

Interactions

Answer 5

• Adverse effects are more pronounced when they are combined with other drugs that have antimuscarinic effects such as TCA

Question 6

Antimuscarinics- CV and GI uses

Prescription

Answer 6

• For bradycardia- Atropine is usually preferred and is given IV in incremental doses (300-600mcg every 1-2 mins) until an acceptable HR is restored
• Glycopyrronium is an alternative, it doesn not cross BBB so no drowsiness
• For IBS, an antimuscarinic is taken orally on a regular basis: hyoscine butylbromide (buscopan) 10mg 8H
• For control of respiratory secretions- hydrobromide is given SC inj or inf

Question 7

Antimuscarinics- CV and GI uses

Monitoring

Answer 7

• When using antimuscarinics to increase HR, High-intensity monitoring (include 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 acheive the optimal balance between beneficial and adverse effects

Question 8

Mebeverine

Common indications

Answer 8

1. Adjunct in GI disorders with muscle spasms
2. IBS

Question 9

Mebervine

MOA

Answer 9

• Mebeverine is a musculotropic antispasmodic drug with a direct action on the smooth muscle of the gastrointestinal tract, without affecting normal gut motility.
• The exact mechanism of action is not known, but multiple mechanisms, such as a decrease in ion channel permeabilities, blockade of noradrenaline reuptake, a local anaesthetic effect, changes in water absorption as well as weak anti-muscarinergic and phosphodiesterase inhibitory effect might contribute to the local effect of mebeverine on the gastrointestinal tract

Question 10

Mebeverine

Adverse effects

Answer 10

• Angioedema
• Face oedema
• Skin reactions

Question 11

Mebeverine

Warnings

Answer 11

• Contraindicated in paralytics ileus (a side effect of clozapine)
• NB- ?no significant interactions

Question 12

Peppermint oil

Indications

Answer 12

• Relief of abdominal colic (lots of unexplained crying in infants) and distension, particularly in IBS

Question 13

Peppermint oil

MOA

Answer 13

• Unknown spasmolytic action on smooth muscle in the GIT
• Peppermint oil seems to increase bile production
• The choleretic and anti-foaming effect play a role in the antispasmodic actions, decreasing abdominal distention and discomfort

Question 14

Peppermint oil

Adverse effects

Answer 14

• Ataxia, tremor
• Bradycardia
• GI discomfort, GORD, N&V
• Rash, Paraesthesia (Pins and needles)

Question 15

Peppermint oil

Warnings + Interactions

Answer 15

• Sensitivity to menthol
• NB- capsules should not be chewed/crushed as peppermint oil can irritate the mouth + oesophagus
• Interaction: Lomitapide (hypercholestrolaemia)