Skeletal Muscle Relaxants

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Skeletal Muscle Relaxants Important Notes

1. Skeletal Muscle Relaxants Classification

  • Drugs acting centrally
    • Diazepam, Baclofen
  • Drugs acting peripherally at the neuromuscular junction
    • Competitive blockers
      • D-tubocurarine, Pancuronium, Rocuronium
  • Depolarising blockers
    • Succinylcholine
  • Drugs acting directly on muscle
    • Dantrolene

Read And Learn More: Pharmacology Question and Answers

2. Succinylcholine

  • It is depolarizing peripherally acting muscle relaxant
  • Induces rapid, complete, and predictable paralysis with spontaneous recovery
  • The onset of action – 1-1.5 min
  • Adverse drug reactions
    • Post-operative muscel pain
    • Hyperkalaemia
    • Cardiac arrhythmias
    • Malignant hyperthermia

3. Non-depolarizing muscle relaxant

  • Long acting – d-tubocurarine, Pancuronium
  • Intermediate-acting – vecuronium, atracurium
  • Short-acting – mivacurium

4. Tubocurarine

  • Releases histamine from mast cells
  • This contributes to hypertension, flushing, and bronchospasm
  • Tubocurarine is administered 4
  • In case of poisoning, neostigmine is used

Skeletal Muscle Relaxants Long Essays

Question 1. Classify skeletal muscle relaxants. Describe the pharmacological actions, therapeutic uses, and adverse effects of d-tubocurarine.
or
List two classes of skeletal muscle relaxants acting at the neuromuscular junction. Mention two therapeutic uses of peripheral-acting muscle relaxants.

Answer:

Skeletal muscle relaxants:

  • Skeletal muscle relaxants are drugs that act peripherally at the neuromuscular junction or muscle fiber itself or centrally in the cerebrospinal axis to reduce muscle tone and/or cause paralysis.

Skeletal muscle relaxants Classification:

1. Peripherally acting muscle relaxants.

  • Neuromuscular blocking agents.
    • Non-depolarizing blockers.
      • Long acting – d-tubocurarine, pancuronium.
      • Intermediate-acting – vecuronium, atracurium
      • Short-acting – mivacurium.
    • Depolarizing blockers.
      • Succinylcholine, Decamethonium

2. Directly acting agents.

  • Dantrolene sodium, Quinine.

3. Centrally acting agents.

  • Mephenesin congeners- Mephenesin, carisoprodol.
  • Benzodiazepines – Diazepam.
  • GABA derivatives – baclofen.
  • Central α2 agonist – Tizanidine.

4. Tubocurarine:

It is a peripherally acting, non-depolarizing skeletal muscle relaxant.

Pharmacological Actions:

1. Skeletal muscle.

  • Intravenous injection initially causes muscular weakness followed by flaccid paralysis.
  • It acts at the neuromuscular junction preventing the combination of acetylcholine released from the motor never ending with its receptors.

2. CVS

  • Causes hypotension.

3. Histamine – causes its release.

4. Autonomic ganglia.

  • In high doses, blocks the autonomic ganglia and adrenal medulla resulting in hypotension.

5. GIT

  • Enhances postoperative paralytic ileus after abdominal operations.

Skeletal muscle relaxants Uses:

  • As an adjuvant to general anesthesia.
  • In dentistry for setting mandibular fractures.
  • Assisted ventilation of critically ill patients in the ICU.
  • To avoid convulsions and trauma from electroconvulsive therapy.
  • In severe cases of tetanus and status epilepticus.

Skeletal muscle relaxants Adverse Effects:

  • Respiratory paralysis and prolonged apnea.
  • Flushing
  • Hypotension and cardiovascular collapse.
  • Precipitation of asthma with histamine release.

Skeletal Muscle Relaxants Short Essays

Question 1. Compare d-tubocurarine and succinylcholine.

Answer:

Skeletal Muscle Relaxants Compare d-tubocurarine And Succinylcholine

Question 2. Compare succinylcholine and pancuronium.

Answer:

Skeletal Muscle Relaxants Compare Succinylcholine And Pancuronium

Question 3. Describe the uses of centrally and peripherally acting skeletal muscle relaxants.

Answer:

Uses of centrally acting skeletal muscle relaxants:

  • During acute muscle spasms, it is used along with anal¬gesics.
  • Used to cure torticollis, backache, and neuralgia.
  • Used to relieve anxiety and tension.
  • Used in spastic neurological disorders like hemiplegia, and paraplegia.
  • During tetanus IV diazepam is given.
  • During electroconvulsive therapy, diazepam is used to suppress convulsions.
  • Used in orthopedic surgery like mandibular fractures.

Uses of peripherally acting skeletal muscle relaxant:

  • As an adjuvant to general anesthesia.
  • To promote skeletal muscle relaxation during abdominal surgery.
  • In dentistry to treat the mandibular fracture.
  • Used in severe cases of tetanus and status epilepticus.
  • Useful in laryngoscopy, bronchoscopy esophagoscopy, and tracheal intubation.
  • To facilitate artificial ventilation of critically ill patients in the ICU.

Question 4. Succinylcholine.

Answer:

Succinylcholine is a peripherally acting skeletal muscle relaxant.

  • It is depolarizing neuromuscular blocking agent

Succinylcholine Mechanism of action:

Succinylcholine
↓
Stimulation of nicotinic receptors
↓
Depolarization of skeletal muscle membrane.
↓
Persistent depolarization.
↓
Results In flaccid paralysis

  • This Is PHASE – 1 block.
  • At high doses, dual block occurs.

Phase -1 block
↓
Initial depolarization
↓
Phase – 2 Nondepolarizing block.

Succinylcholine Adverse Effects:

  • Increases intraocular pressure.
  • Postoperative muscle pain – common
  • Hyperkalemia.
  • Cardiac arrhythmia.
  • Apnea.
  • Malignant hyperthermia – genetically determined
    .

Skeletal Muscle Relaxants Short Answers

Question 1. Pancuronium.

Answer:

Pancuronium is a peripherally acting skeletal muscle relaxant

  • It is a long-acting, non-depolarizing competitive neuro-muscular blocking agent

Pancuronium Uses:

  • As an adjuvant to general anesthesia.
  • Used to promote skeletal muscle relaxation during abdominal surgery.
  • Used in the treatment of mandibular fractures.
  • In severe cases of tetanus and status epilepticus.
  • Duration of action – 60 – 120 min.
  • The onset of action – 4 – 6 min.
  • Dose – 0.04 – 0.1 mg/kg of body weight

Question 2. Lioresal.

Answer:

It is the trad$ name of baclofen, which is an analog of the inhibitory transmitter GABA.

Lioresal Mechanism:

  • The primary site of action is the spinal cord.
  • It depresses poly-synaptic and mono-synaptic reflexes.

Lioresal Uses:

  • Reduces spasticity in neurological disorders like multiple sclerosis.
  • Improves bladder and bowel functions in patients with spinal lesions.
  • Tried in trigeminal neuralgia.

Lioresal Adverse effects:

  • Drowsiness, weakness, ataxia,
  • Abrupt withdrawal causes anxiety, palpitation, and hallucinations.
  • Dose: 10 mg BD to 25 mg TDS

Viva Voce:

1. Diaphragm is most resistant to succinylcholine

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