Antispasmodic Agents

Antispasmodics are a group of medications used to reduce excessive GI smooth muscle contractility and spasm. These medications may be helpful in those with abdominal pain due to conditions such as irritable bowel syndrome, although their efficacy is controversial. Antispasmodics are classified based on their action; they include anticholinergics and direct smooth muscle relaxants. Anticholinergics block muscarinic receptor activity in the enteric nervous system and on smooth muscle cells, but can also have systemic anticholinergic side effects (e.g., urinary retention, blurred vision, xerostomia, tachycardia). Direct smooth muscle relaxants have a variety of potential effects, but notably, they act directly on smooth muscle cells. These medications are not associated with anticholinergic side effects.

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Antispasmodics are a group of medications used to reduce excessive GI smooth muscle contractility and spasm.


Antispasmodic agents are classified based on their action:

  • Anticholinergics
    • Dicyclomine
    • Hyoscyamine
    • Atropine
  • Direct smooth muscle relaxation
    • Mebeverine
    • Pinaverium
    • Peppermint oil


This group of medications is used in individuals with abdominal discomfort from bowel spasm, such as that due to irritable bowel syndrome (IBS).

  • Provides short-term relief
  • Efficacy has not been convincingly established.


Mechanism of action

  • This group of medications blocks acetylcholine’s action at muscarinic receptors: 
    • In the enteric nervous system
    • On smooth muscle cells
  • Results in ↓ smooth muscle contractions and motility


  • Dicyclomine
    • Absorption: rapid
    • Metabolism: unclear
    • Excretion: urine (primary) and feces
  • Hyoscyamine
    • Absorption: rapid
    • Metabolism: hepatic
    • Excretion urine

Adverse effects

Side effects of these drugs are due to their anticholinergic properties, and are usually associated with higher doses.

  • Constipation 
  • Urinary retention
  • Mydriasis and blurred vision
  • Xerostomia
  • Dizziness
  • Nausea and vomiting
  • Drowsiness
  • Nervousness
  • Tachycardia


  • Hypersensitivity
  • GI obstruction
  • Severe ulcerative colitis
  • Paralytic ileus
  • Glaucoma
  • Myasthenia gravis
  • Breastfeeding (generally avoided in breastfeeding women)
  • Obstructive uropathy

Direct Smooth Muscle Relaxants

Mechanism of action

  • This group of medications acts directly on intestinal smooth muscle cells
  • Mebeverine: mechanism is unknown, but may cause:
    • ↓ Ion channel permeability
    • Noradrenaline reuptake blockade
    • Weak antimuscarinic effect
    • Phosphodiesterase inhibition
    • Anesthetic effect
  • Peppermint oil: calcium channel blocker
  • Results in smooth muscle relaxation and ↓ motility


The following pharmacokinetics are reported for mebeverine:

  • Absorption: rapid
  • Distribution: 75% albumin-bound
  • Metabolism: 1st pass
  • Excretion: urine (as metabolites)

Adverse effects


  • Heartburn
  • Dizziness
  • Rash


  • Nausea and vomiting
  • Constipation
  • Headache
  • Dizziness

Peppermint oil:

  • Burning mouth syndrome
  • Mouth sores
  • Flushing
  • Interstitial nephritis and renal failure


Contraindications for mebeverine include:

  • Hypersensitivity
  • Breastfeeding (generally avoided in breastfeeding women)


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