Antimuscarinics and other Gut Antispasmodics

Antispasmodics are primarily used to treat irritable bowel syndrome (IBS). They include:

• Antimuscarinics (anticholinergics) - these act as smooth muscle relaxants, reducing gut spasm and intestinal motility. They include:
  • Atropine sulphate
  • Dicycloverine hydrochloride
  • Propantheline bromide
  • Hyoscine butylbromide
  They are poorly selective for gut smooth muscle and so antimuscarinic side-effects are common.
  Dicycloverine hydrochloride has much less antimuscarinic action than atropine and also has some direct action on smooth muscle making it preferable to atropine which commonly causes antimuscarinic side-effects.
  Propantheline bromide is an alternative to hyoscine butylbromide but is prescription only and has not been studied in IBS.¹
• Alverine, mebeverine and peppermint oil - these drugs are thought to have a direct inhibitory effect on smooth muscle. Peppermint oil may exert an inhibitory effect on the calcium channels in the gut.² Their selectivity means there are relatively few side-effects.¹

Irritable bowel syndrome

• Management of patients with IBS includes reassurance and explanation, lifestyle modifications (reducing dietary fat, caffeine avoiding dietary triggers; exercise and altering defecation patterns), non-pharmacological therapies (education, coping strategies, relaxation therapies, hypnotherapy, cognitive behaviour therapy, biofeedback training) and pharmacological therapies.^1,3
• The British Society of Gastroenterologists (BSG) advises that current drug treatments are of limited value but that specific symptoms may respond in some patients to particular drugs.³ Predominant symptoms (abdominal pain, diarrhoea or constipation) should be used to guide drug selection: antispasmodics are considered first line where abdominal pain or bloating without distention are the chief complaint(s).
• There is some evidence of benefit from mebeverine and hyoscine in reducing pain (NNT 8) and patients' overall assessment of their IBS symptoms. There is no RCT evidence of alverine's efficacy and dicycloverine's use is limited by its side-effects.³ There is limited evidence of peppermint oil's benefit in IBS.⁴
• There is only weak evidence for the use of antispasmodics in the treatment of IBS/recurrent abdominal pain in children⁵ and they are not licensed for this use in younger children.

Diverticular disease

Antispasmodics such as mebeverine, alverine and peppermint oil have sometimes been used for pain-relief in diverticular disease.
However, there is no good evidence for their efficacy and they are no longer recommended.⁶ IBS and diverticular disease can be hard to distinguish clinically and antispasmodics may be of some use where there are co-existent symptoms suggestive of IBS e.g. abdominal pain related to defecation, abdominal bloating or rectal mucus.

Radiology

Hyoscine butylbromide is sometimes used to overcome acute gut spasm in diagnostic procedures, given by im or slow iv injection.⁷

Include:

• Known hypersensitivity or allergy to drug or excipient (e.g. Colpermin® contains arachis oil).
• Antimuscarinics should not be used in:
  • Narrow-angle glaucoma
  • Myasthenia gravis
  • Paralytic ileus
  • Megacolon
  • Pyloric stenosis
  • Prostatic enlargement
• Alverine and mebeverine should not be used in paralytic ileus, intestinal obstruction, faecal impaction, colonic atony or porphyria.
• Antimuscarinics should be used with caution in those with a tachycardia - e.g. hyperthyroidism, cardiac insufficiency or failure.
• Antimuscarinics may decrease sweating so should be used with caution in those with a fever.
• Antimuscarinics should be used with care in those with Down's syndrome, in children and the elderly as these patient groups are more susceptible to side-effects.
• Antimuscarinics should be used with caution in:
  • Gastro-oesophageal reflux disease
  • Diarrhoea
  • Ulcerative colitis
  • Acute MI
  • Hypertension
• Pregnancy and breastfeeding - limited safety data as regards safety.
• Peppermint oil should not be used in those with cholecystitis and may exacerbate symptoms in those with a hiatus hernia or significant gastro-oesophageal reflux disease.²

• Predictable and common antimuscarinic side-effects include:
  • Constipation
  • Blurred vision
  • Urinary retention
  • Tachycardia
  • Dry mouth
  • Flushing
  • Dryness of the skin
  Confusion, nausea, vomiting and giddiness occur less commonly but are more likely to affect the elderly. These types of side-effect are generally mild and self-limiting with hyoscine butylbromide.
• Alverine and mebeverine can cause flatulence and bloating. These side-effects usually diminish during continued treatment.
• Peppermint oil can cause heartburn and perianal irritation. Capsules should be swallowed, not broken or chewed as the oil can directly irritate the mouth or oesophagus.

• Discuss the limitations of current drug treatments for IBS. Antispasmodics may be helpful to some individuals - in particular those where abdominal pain predominates symptoms but are not effective in all. Patients should see drug therapy as one component of treatment.
• Advise antispasmodics may be used on "as required" basis or up to three times a day for acute attacks of pain or before meals if postprandial symptoms predominate.
• There is no consensus as to duration of treatment - most trials to date have been short (less than 2 months).
• Where there is no response to one anti-spasmodic, it is worth considering a switch to another - different agents may suit different individuals.
• Outline possible or important side-effects e.g. to seek urgent advice if they develop a painful red eye with loss of vision whilst taking an antimuscarinic (as glaucoma may be precipitated).