How do Antispasmodics Work?

Different types of antispasmodic medications work by different mechanisms. In the U.S., the most commonly used antispasmodics come from a class of drugs called antimuscarinics. These drugs act on your parasympathetic nervous system to block the signals that activate your smooth muscles.

Types of Antispasmodics

Antispasmodics can be classified into two main categories:

1. Gastrointestinal (GI) Antispasmodics

These are used to relieve spasms and cramping in the stomach and intestines. Commonly prescribed for conditions like Irritable Bowel Syndrome (IBS) and abdominal pain.

• Anticholinergic Antispasmodics: Block acetylcholine, reducing muscle contractions and secretions.
  • Examples:
    • Dicyclomine (Bentyl)
    • Hyoscyamine (Levsin)
    • Propantheline
• Direct-Acting Smooth Muscle Relaxants: Act directly on smooth muscle to relieve spasms.
  • Examples:
    • Mebeverine (used in IBS)
    • Alverine Citrate

2. Urinary Antispasmodics

These are used to manage conditions like overactive bladder (OAB) or urinary incontinence by relaxing bladder muscles.

• Examples:
  • Oxybutynin (Ditropan)
  • Tolterodine (Detrol)
  • Mirabegron (Myrbetriq)

Antispasmodics are a group of medications used to relieve or prevent muscle spasms, which are involuntary and often painful contractions of muscles. These drugs primarily target smooth muscle spasms found in the gastrointestinal (GI) tract, bladder, uterus, or other internal organs, as well as occasionally in skeletal muscles.

How Antispasmodics Work

Antispasmodics work by reducing or preventing muscle spasms, which are involuntary and often painful contractions of muscles. These drugs primarily target smooth muscle (involuntary muscles found in internal organs like the stomach, intestines, and bladder). Their mechanism of action depends on the specific type of antispasmodic.

Antispasmodics can be classified into two main types based on how they work:

1. Anticholinergic Antispasmodics

These drugs block the action of acetylcholine, a neurotransmitter that stimulates smooth muscle contractions. By inhibiting acetylcholine, they reduce the spasms and overactivity of smooth muscles.

• How They Work:
  • Block muscarinic receptors in the smooth muscle.
  • Reduce parasympathetic nerve activity, which controls involuntary muscle contractions.
  • Result: Relaxation of smooth muscles, reduced secretions, and slower movement in the affected organs.
• Examples:
  • Dicyclomine (Bentyl): Used for irritable bowel syndrome (IBS).
  • Hyoscyamine: Reduces intestinal and bladder spasms.
  • Propantheline: Treats hypermotility disorders of the GI tract.

2. Direct Smooth Muscle Relaxants

These drugs act directly on the smooth muscles themselves to relax them. They do not interfere with nerve signals but instead modify the muscle’s ability to contract.

• How They Work:
  • Alter ion channels (e.g., calcium channels) to reduce muscle contractility.
  • Reduce the muscle’s response to stimuli, leading to relaxation.
  • Result: Direct relief of spasms without affecting nerve activity.
• Examples:
  • Mebeverine: Commonly used for IBS.
  • Alverine Citrate: Relieves abdominal cramping and discomfort.

3. Other Mechanisms

Certain antispasmodics use unique mechanisms depending on their target organ or application:

• Beta-3 Adrenergic Agonists (e.g., Mirabegron):
  • Work on beta-3 receptors in the bladder to reduce spasms and increase bladder capacity.
• Calcium Channel Modulators:
  • Decrease calcium influx into smooth muscle cells, reducing contractions.

Other types of antispasmodics work directly on the smooth muscles in your gut (your stomach and intestines).

• Antimuscarinics: Also called anticholinergics, these antispasmodic drugs work by blocking certain nerve cells from receiving certain signals. Nerve cells (chemoreceptors) receive chemical messages (neurotransmitters) that tell your smooth muscles to contract. Antimuscarinic drugs block these messages, preventing the muscles from contracting.
• Calcium channel blockers: While they aren’t technically classified as antispasmodics, calcium channel blockers relax your smooth muscles by inhibiting calcium uptake. Smooth muscles need calcium to contract, so limiting calcium access reduces contractions. These drugs can affect the smooth muscles in your blood vessels as well as in your gut. U.S. healthcare providers don’t prescribe them for gut-related conditions, but providers in other countries sometimes do.
• Direct smooth muscle relaxants: These are medications that target the muscles in your gut specifically. They work by inhibiting calcium and sodium uptake in these muscles, which the muscles need to contract. Direct smooth muscle relaxants include some prescription drugs available in other countries, but not in the U.S. They also include certain essential oils, like peppermint oil, which work the same way.