Muscle relaxers (also called muscle relaxants) are prescription medications that affect muscle function. Healthcare providers prescribe them to treat several symptoms, such as muscle spasms, spasticity and musculoskeletal pain.
The term “muscle relaxant” refers to two major drug classes: antispastics and antispasmodics. These two classes differ in their uses, ways of working and side effects.
This article focuses on skeletal muscle relaxants, as opposed to smooth muscle relaxants. Skeletal muscles are the muscles that help you move. Smooth muscles are the muscles that you don’t have control over, like the muscles in your intestine, stomach and blood vessels. There are also smooth muscle antispasmodic medications.
There Are Two Types of Muscle Relaxnt : Antispasmodics and Antispastics.
Antispastics directly affect the spinal cord or the skeletal muscles with the aim of improving muscle tightness and spasms.
Antispasmodics help reduce muscle spasms via the central nervous system. They inhibit the transmission of neurons in the brain.
Antispastics and antispasmodics have different indications and side effects. Since these drugs work differently, a person should never use them interchangeably or substitute one type for another.
Antispasmodics
Antispasmodics are drugs used to relieve muscle spasms in smooth muscles, which are found in the walls of organs such as the intestines, stomach, and bladder. They are commonly prescribed for gastrointestinal and urinary conditions.
- Examples:
- Dicyclomine: Used for irritable bowel syndrome (IBS).
- Hyoscyamine: Used to treat bladder spasms and cramping.
- Oxybutynin: Helps with overactive bladder symptoms.
- Mechanism of Action:
- They work by blocking nerve signals or reducing the contractility of smooth muscles.
- Can act via anticholinergic effects, decreasing parasympathetic activity.
- Uses:
- Irritable bowel syndrome (IBS)
- Urinary incontinence or bladder spasms
- Menstrual cramps
- Diverticulitis
Antispastics
Antispastics are a specific type of medication designed to reduce spasticity, which refers to the stiffness or uncontrolled tightening of muscles often seen in conditions that affect the central nervous system (CNS). These drugs are commonly used to manage spasticity in neurological conditions such as multiple sclerosis (MS), cerebral palsy, stroke, or spinal cord injuries.
How Antispastics Work
Antispastics work by either:
- Acting on the CNS to reduce the signals that cause muscle overactivity.
- Acting directly on muscles to relax them and reduce stiffness.
Common Antispastic Drugs
- Baclofen
- Acts on the spinal cord by activating GABA receptors, reducing muscle overactivity.
- Often used in multiple sclerosis and spinal cord injuries.
- Tizanidine
- Alpha-2 adrenergic agonist that decreases nerve signals to reduce muscle spasticity.
- Effective for conditions like MS or stroke-induced spasticity.
- Dantrolene
- Works directly on skeletal muscle by interfering with calcium release, reducing muscle contractions.
- Used in conditions like malignant hyperthermia or chronic spasticity.
- Diazepam (a benzodiazepine)
- Enhances GABA activity, reducing muscle stiffness and spasm.
- Can be used for spasticity but has sedative side effects.
- Botulinum Toxin (Botox)
- Blocks nerve signals at the neuromuscular junction, causing temporary muscle relaxation.
- Used for focal spasticity (specific muscle groups).
Types of Muscle Relaxants
Muscle relaxants can be divided into two categories based on their mechanism of action:
1. Centrally Acting Muscle Relaxants
These medications work on the central nervous system (brain and spinal cord) to reduce muscle stiffness or spasm. They are typically used for acute muscle pain or spasticity caused by neurological conditions.
- Examples:
- Cyclobenzaprine (Flexeril): Commonly used for muscle spasms due to injury or strain.
- Methocarbamol (Robaxin): Reduces skeletal muscle spasms with fewer sedative effects.
- Carisoprodol (Soma): For short-term use in muscle pain but has a risk of dependency.
- Tizanidine (Zanaflex): Primarily for spasticity in conditions like multiple sclerosis.
- Diazepam (Valium): A benzodiazepine that relaxes muscles and reduces anxiety but is sedative.
- Baclofen: Reduces spasticity in neurological disorders like spinal cord injury or MS.
- Uses:
- Muscle spasms caused by injury or strain.
- Spasticity due to conditions like multiple sclerosis or cerebral palsy.
- Pain relief in conditions like fibromyalgia.
2. Peripherally Acting Muscle Relaxants
These drugs act directly on the muscle fibers or the neuromuscular junction to reduce muscle tone or spasm.
- Examples:
- Dantrolene (Dantrium): Used to treat spasticity and conditions like malignant hyperthermia.
- Botulinum Toxin (Botox): Blocks nerve signals to relax muscles, often for focal spasticity.
- Uses:
- Spasticity due to stroke, brain injury, or spinal cord injury.
- Malignant hyperthermia.
- Focal dystonia or spasticity.