Relaxing Skeletal Muscle

Chapter 8: Drugs for Relaxing Skeletal Muscle

Overview of Muscle Spasm

• Definition of Muscle Spasm:

  • Involuntary localized contractions of muscles.

  • Often associated with pain, trauma, or inflammation within the muscle.

• Accompanying Symptoms:

  • Pain is commonly present alongside spasms.

• Treatment Options:

  • Nonpharmacologic Approaches:

  • Physical therapy, heat application, etc.

  • Pharmacologic Approaches:

  • Skeletal muscle relaxants.

  • Analgesics for pain relief.

Muscle Spasm Cycle

• Initiators of Muscle Spasm Cycle:

  • Muscle can be:

  • Over-contracted

  • Over-exercised

  • Over-stretched or injured

• Consequences of Muscle Spasm Cycle:

  • Venous drainage of muscle is compromised.

  • Lactic acid accumulates in the muscle, causing increased muscle tone.

  • Cycle reinforces itself, leading to further spasticity and muscle hardening.

• Implications of Muscle Spasm:

  • Compressed nerves and vessels may result from spasm.

  • Can lead to:

  • Pain and discomfort.

  • Impeded blood flow to muscles and organs.

  • Decreased joint mobility.

  • Reflex organ dysfunction.

  • Overall poor health outcomes.

• Feedback Loop to the Brain:

  • Excess lactic acid can negatively impact nerve feedback to the brain.

  • Brain interprets weakened signals as insufficient muscle tone, prompting commands that further increase muscle tone.

Skeletal Muscle Relaxants

• List of Skeletal Muscle Relaxants:

  • Carisoprodol

  • Tizanidine

  • Cyclobenzaprine

  • Diazepam

  • Metaxalone

  • Baclofen

  • Methocarbamol

  • Orphenadrine

  • Chlorzoxazone

Mechanism of Action

• General Mechanism:

  • The exact mechanism of action for most skeletal muscle relaxants is unknown.

  • Most act through the Central Nervous System (CNS).

• Side Effects of CNS Action:

  • Drowsiness and sedation are common among these medications.

• Example of Benzodiazepines:

  • Diazepam is a benzodiazepine that acts on GABA receptors.

  • Inhibits nerve impulse transmission within the CNS.

Therapeutic Uses

• Primary Goals of Muscle Relaxants:

  • Relieving muscle spasms.

  • Managing accompanying pain.

  • Increasing range of motion.

  • Selection based on adverse effects and physician/patient preferences.

Adverse Effects

• Common Side Effects:

  • Drowsiness and dizziness are the most frequently reported.

  • Potential for diminished liver and kidney function.

  • Hypersensitivity reactions can occur.

  • Risk of physical dependence should be considered.

  • Anticholinergic effects may arise.

Central Nervous System Depression

• Potential Outcomes:

  • Symptoms may include drowsiness, dizziness, and sedation.

  • Respiratory depression can occur at higher doses.

  • Severe risks such as coma and death can occur in overdose situations.

• Drug-Drug Interactions:

  • Alcohol can exacerbate CNS depressant effects of muscle relaxants.

Physical Dependence

• Risk of Dependence:

  • More likely with centrally acting skeletal muscle relaxants, especially at higher doses and prolonged use.

  • Gradual discontinuation is necessary to prevent withdrawal syndrome.

Anticholinergic Adverse Effects

• Mechanism of Action:

  • Associated with blockade of muscarinic cholinergic receptors in the body.

• Specific Adverse Effects:

  • Blurred vision and pupil dilation.

  • Increased intraocular pressure.

  • Increased heart rate.

  • Gastrointestinal issues like constipation.

  • Urinary hesitancy and retention.

  • Dry mouth and decreased sweating.

Other Adverse Effects

• Specific Drug Effects:

  • Chlorzoxazone and methocarbamol may cause urine discoloration.

  • Diazepam has abuse potential and is classified as a Schedule IV controlled substance.

Role of the Athletic Trainer

• Responsibilities in Medication Management:

  • Ensuring medication adherence among athletes.

  • Monitoring for adverse effects from muscle relaxants.

  • Being aware of potential drug interactions that may affect treatment outcomes.