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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Overview

Definition

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

Classification

Antispasmodic agents are classified based on their action:

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

Indications

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.

Anticholinergics

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

Pharmacokinetics

  • 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

Contraindications

  • 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

Pharmacokinetics

The following pharmacokinetics are reported for mebeverine:

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

Adverse effects

General:

  • Heartburn
  • Dizziness
  • Rash

Mebeverine:

  • Nausea and vomiting
  • Constipation
  • Headache
  • Dizziness

Peppermint oil:

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

Contraindications

Contraindications for mebeverine include:

  • Hypersensitivity
  • Breastfeeding (generally avoided in breastfeeding women)

References

  1. McQuaid KR. (2017). Drugs used in the treatment of gastrointestinal diseases. In Katzung BG, et al. (Eds.), Basic & Clinical Pharmacology. New York: McGraw-Hill Medical, pp. 1101-1103
  2. Sharkey KA, MacNaughton WK. (2017). Gastrointestinal motility and water flux, emesis, and biliary and pancreatic disease, in Goodman and Gillman, The Pharmacological Basis of Therapeutics. New York: McGraw-Hill Medical, p. 934
  3. Dicyclomine. Medscape. Retrieved June 24, 2021, from https://reference.medscape.com/drug/bentyl-dicyclomine-341987#5
  4. Hyoscyamine. Medscape. Retrieved June 24, 2021, from https://reference.medscape.com/drug/levbid-levsin-hyoscyamine-341990#5
  5. Tripathi KD. Chapter 8: Anticholinergic drugs and drugs acting on autonomic ganglia, in Essentials of Medical Pharmacology. JP Medical Ltd; 2018, p.128
  6. Annaházi A, Róka R, Rosztóczy A, Wittmann T. (2014). Role of antispasmodics in the treatment of irritable bowel syndrome. World Journal of Gastroenterology. 20(20): 6031–43. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4033443/
  7. Darvish-Damavandi M, Nikfar S, Abdollahi M. (2010). A systematic review of efficacy and tolerability of mebeverine in irritable bowel syndrome. World Journal of Gastroenterology. 16 (5): 547–53. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2816265/
  8. U.S. Department of Health & Human Services (n.d.). Mebeverine. Retrieved July 11, 2021, from https://drugs.ncats.io/drug/7F80CC3NNV
  9. Wald A. (2020). Treatment of irritable bowel syndrome in adults. In Grover S. (Ed.), UpToDate. Retrieved July 11, 2021, from https://www.uptodate.com/contents/treatment-of-irritable-bowel-syndrome-in-adults
  10. Kligler B, Chaudhary S. (2007). Peppermint oil. American Family Physician. 75(7):1027-1030. https://www.aafp.org/afp/2007/0401/p1027.html

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