Skeletal Muscle Relaxant_Spring

Muscle Relaxers Overview

  • Presented by: Dr. Sandra Joiner

Muscle Relaxants Overview

  • Primarily used for:

    • Back pain

    • Muscle spasms

    • Cramps

Common Muscle Relaxants

  • Centrally Acting Skeletal Muscle Relaxants:

    • Baclofen (Lioresal)

    • Carisoprodol (Soma)

    • Chlorzoxazone (Paraflex)

    • Cyclobenzaprine (Flexeril)

    • Methocarbamol (Robaxin)

    • Orphenadrine (Banflex, Flexoject)

    • Tizanidine (Zanaflex)

  • Direct Acting Skeletal Muscle Relaxants:

    • Botulinum toxin type A (Botox)

    • Botulinum toxin type B (Myobloc)

    • Dantrolene (Dantrium)

    • Incobotulinumtoxin A (Xeomin)

Muscle Spasm

  • Definition: A disturbance in the CNS caused by diseases, infections, toxins, or injuries.

  • Results in involuntary muscle contractions due to:

    • Overstretching

    • Joint wrenching

    • Tendon or ligament tearing

  • Pain mechanism:

    • Accumulation of lactic acid from reduced blood flow during contractions.

  • Treatment: Antispasmodic agents are used for musculoskeletal pain.

Muscle Spasticity

  • Definition: Occurs with damaged neurons in the CNS, leading to permanent abnormalities.

  • Results in:

    • Hypertonia: Excessive muscle stimulation

    • Loss of coordinated muscle activity

  • Conditions treated: Chronic conditions like Cerebral Palsy and Upper Motor Neuron disorders.

Anti-Spasmodic Agents

  • Carisoprodol:

    • Schedule: IV, high abuse potential

    • Action: Blocks interneural activity; depresses neuronal transmission.

    • Adverse Effects (AEs): Sedation, dizziness, headache, GI discomfort.

  • Cyclobenzaprine (Flexeril):

    • 1st line therapy for skeletal muscle relaxation; economical.

    • Mechanism: Structurally related to TCA; acts as 5HT3 antagonist.

    • Effects: Sedation; potentiates norepinephrine, may increase HR.

    • Cautions: Avoid MAO-I within 14 days; enhances effects of alcohol and other depressants.

  • Metaxolone (Skelaxin):

    • Minimal side effects; low sedation potential.

    • Use: Adjunct to physical therapy; monitor hepatic and renal function.

  • Methocarbamol (Robaxin):

    • Indicated for acute, painful musculoskeletal conditions.

    • Also treats tetanus in children (not 1st line).

    • AEs: Anaphylaxis, seizures, leukopenia.

Anti-Spastic Agents

  • Baclofen:

    • Agonist at GABA receptors in CNS.

    • Used for upper motor neuron spasticity.

    • Effective with fewer sedative effects compared to Diazepam.

    • Administration: Oral or intrathecal (with black box warning).

    • CIs: Diabetes mellitus, preexisting psychiatric conditions.

  • Dantrolene:

    • Directly acts without affecting neuromuscular transmission.

    • Mechanism: Blocks ryanodine receptors; no Ca++ release.

    • Uses: Upper Motor Neuron disorders; malignant hyperthermia.

    • AEs: Sedation, malaise, lightheadedness, hepatotoxicity.

Use in Special Populations

  • Children:

    • Safety and efficacy are not established.

    • Baclofen is used for cerebral palsy; Methocarbamol for tetanus.

  • Adults:

    • Use caution in activities requiring alertness; diazepam can be used for anxiety-related spasms.

    • Pregnant/lactating women should use alternatives.

  • Older Adults:

    • Higher risk of AEs; Carisoprodol is preferred for those with hepatic or renal impairment.

Dual Action Medications

  • Tizanidine (Zanaflex):

    • Treats muscle spasms and spasticity; not 1st line for neck/back pain.

    • AEs: Urinary retention; hypotension risks.

  • Diazepam (Valium):

    • Treats pain from spasms; has multiple CNS actions.

  • Botulinum toxin (OnabotulinumtoxinA):

    • Acetylcholine release inhibitor; treats various spastic conditions.

    • AEs: Risks of anaphylactic reactions.

Review Questions

  1. Centrally Acting Muscle Relaxant for Tetanus in Children?

    • Options: Botulinum Toxin type B, Dantrium, Baclofen, Methocarbamol

  2. Baclofen Taper Duration to Prevent Psychosis?

    • Options: 12-21 days, 1-10 days, 7-14 days, 7-21 days

  3. Patient with Botulinum Toxin A Complains of Headache?

    • Options: Provide comfort/measure safety, Assess for possible anaphylactic reactions.