Antispastic

Antispastic medications are drugs specifically designed to reduce muscle spasticity, a condition characterized by increased muscle stiffness and uncontrolled, repetitive contractions caused by damage to the brain or spinal cord. Unlike antispasmodics, which generally treat smooth muscle spasms (e.g., in the gut or bladder), antispastics focus on skeletal muscle spasticity associated with neurological disorders.  These medications aim to improve muscle movement, reduce pain, and enhance overall function in affected individuals.

What Are Antispastic Medications Used For ?

Healthcare providers mainly prescribe antispastic muscle relaxers to treat spasticity.

Spasticity is a disruption in muscle movement patterns that causes certain muscles to contract all at once when you try to move or even at rest. It’s usually caused by damage to nerve pathways within your brain or spinal cord that control movement and stretch reflexes.

Spasticity may occur due to several conditions, some of which include:

• Cerebral palsy.
• Multiple sclerosis (MS).
• Spinal cord injury.
• Stroke.
• Brain or head injury.
• Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease.

Baclofen is considered the first-line treatment for spasticity, especially for adults who have spinal cord injuries.

Antispastic drugs are commonly prescribed for:

1. Neurological Disorders

• Multiple Sclerosis (MS):
  • Helps relieve spasticity caused by nerve damage in the brain or spinal cord.
• Cerebral Palsy:
  • Reduces muscle stiffness, improving mobility and range of motion.
• Stroke:
  • Addresses spasticity that develops as a complication of brain injury.
• Spinal Cord Injuries:
  • Alleviates increased muscle tone and uncontrolled contractions.
• Amyotrophic Lateral Sclerosis (ALS):
  • Manages spasticity to improve quality of life.

2. Genetic Disorders

• Hereditary Spastic Paraplegia (HSP):
  • A rare condition causing progressive spasticity and weakness in the legs.

3. Other Spasticity-Related Conditions

• Traumatic Brain Injury (TBI):
  • Reduces abnormal muscle tone following an injury to the brain.
• Post-Central Nervous System Tumors:
  • Treats spasticity caused by brain or spinal cord tumors.

How Antispastic Medications Work ?

Antispastic medications work by targeting the abnormal muscle stiffness and overactivity (spasticity) caused by neurological conditions. Spasticity results from disrupted communication between the brain, spinal cord, and muscles, leading to excessive muscle contractions. These drugs act at various levels of the nervous system or directly on muscles to reduce spasticity and improve muscle control.

Mechanisms of Action of  Antispastic Medications

Antispastic medications can work in the following ways:

1. Modulating Neurotransmitter Activity

• Central Nervous System (CNS) Acting Drugs:
  • Many antispastics work by influencing the nervous system pathways responsible for muscle tone and movement.
  • They reduce excitatory signals or enhance inhibitory signals to relax overactive muscles.

2. Targeting Specific Receptors

• GABA Receptors:
  • Some drugs enhance the activity of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter.
  • This dampens excessive nerve signals causing muscle spasticity.
  • Examples:
    • Baclofen: Activates GABA-B receptors in the spinal cord to reduce motor neuron excitability.
    • Diazepam: Enhances GABA-A receptor activity, producing muscle relaxation and sedation.
• Alpha-2 Adrenergic Receptors:
  • Drugs like Tizanidine act on these receptors to reduce motor neuron activity in the spinal cord, leading to muscle relaxation.

3. Reducing Muscle Contractility

• Direct Muscle Effects:
  • Some medications work directly on muscle fibers to limit their ability to contract.
  • Example:
    • Dantrolene: Inhibits calcium release from the sarcoplasmic reticulum in muscle cells, which is necessary for muscle contraction.

4. Blocking Nerve Signal Transmission

• Local Action:
  • Certain treatments, such as Botulinum toxin (Botox), block the release of acetylcholine at the neuromuscular junction, preventing muscle contractions in targeted areas.

Summary of Mechanisms

Antispastic Medication Listing

Here’s a comprehensive list of antispastic medications, categorized by their mechanism of action:

1. GABA Agonists

These medications enhance the activity of the inhibitory neurotransmitter GABA, reducing nerve signal transmission that leads to spasticity.

Baclofen

• Brand Names: Lioresal, Gablofen
• Mechanism: Activates GABA-B receptors in the spinal cord.
• Uses: Spasticity from multiple sclerosis (MS), spinal cord injuries, and cerebral palsy.

Diazepam

• Brand Names: Valium
• Mechanism: Enhances GABA-A receptor activity in the CNS.
• Uses: Acute spasticity, including post-injury or stroke-related stiffness.

2. Alpha-2 Adrenergic Agonists

These drugs reduce the release of excitatory neurotransmitters in the spinal cord.

Tizanidine

• Brand Names: Zanaflex
• Mechanism: Stimulates alpha-2 adrenergic receptors to reduce nerve signal transmission.
• Uses: Spasticity from MS, spinal cord injuries, or stroke.

3. Direct Muscle Relaxants

These act directly on skeletal muscle cells to reduce contractions.

Dantrolene

• Brand Names: Dantrium, Revonto
• Mechanism: Inhibits calcium release from the sarcoplasmic reticulum in muscle cells.
• Uses: Chronic spasticity, malignant hyperthermia.

4. Botulinum Toxin (Focal Treatment)

A localized approach for managing spasticity in specific muscle groups.

Botulinum Toxin A (Botox, Dysport, Xeomin)

• Mechanism: Blocks acetylcholine release at the neuromuscular junction.
• Uses: Focal spasticity in conditions like cerebral palsy, stroke, or brain injuries.

Botulinum Toxin B (Myobloc)

• Mechanism: Similar to Botulinum Toxin A but used for certain refractory cases.
• Uses: Localized spasticity.

5. Cannabinoid-Based Medications

Used as adjunct therapy for spasticity when other medications are insufficient.

Nabiximols

• Brand Name: Sativex
• Mechanism: Modulates the endocannabinoid system to reduce muscle spasticity.
• Uses: Spasticity in MS, particularly when resistant to other treatments.

6. Combination Medications

These combine antispastic effects with other therapeutic actions.

Clonazepam

• Mechanism: Enhances GABA-A receptor activity, similar to diazepam.
• Uses: Spasticity, seizures, or anxiety disorders in conjunction with spasticity.

Gabapentin

• Brand Names: Neurontin
• Mechanism: Reduces excitatory neurotransmitter release in the CNS.
• Uses: Neuropathic pain and spasticity in MS or spinal cord injuries.

7. Other Adjunct Therapies

Although not exclusively antispastic, these medications may help manage spasticity indirectly.

• Cyclobenzaprine (Flexeril): Muscle relaxant used for acute conditions; less effective in chronic spasticity.
• Pregabalin (Lyrica): Reduces neuropathic pain and may help with spasticity.
• Phenol or Alcohol Injections: Used to block nerve signals temporarily in focal spasticity.

What are the Possible risks or complications of  Taking Muscle Relaxers?

The two main possible complications of taking muscle relaxers are the potential for overdose and dangerous interactions with alcohol.

Alcohol and muscle relaxers

If you’re taking a prescription muscle relaxer, you shouldn’t consume alcohol. Alcohol and muscle relaxers are both depressants, which means they slow down your central nervous system. If you take them together, the side effects are much more intense, which can be dangerous.

It can cause symptoms like:

• Extreme dizziness.
• Extreme drowsiness.
• Blurred vision.
• Low blood pressure.
• Fainting.
• Memory problems.
• Liver damage.
• Increased risk of overdose

Muscle relaxer overdose

Muscle relaxers have a potential for misuse and addiction, especially carisoprodol and diazepam. Prolonged use can lead to increased tolerance and physical dependence.

As most muscle relaxers act as sedatives, some people take muscle relaxers alone or in combination with other drugs for nonmedical reasons to produce or enhance feelings of euphoria and dissociation.

Muscle relaxer misuse can lead to an increased risk of overdose, which can result in:

• Changes in consciousness.
• Hallucinations.
• Seizures.
• Respiratory depression.
• Cardiac arrest.
• Coma.
• Death.

Seek immediate medical attention if you or a loved one are experiencing symptoms of an overdose.

Related Entries

• Baclofen