1. Skeletal Muscle Relaxants
CHAPTER 9
Skeletal Muscle Relaxants

2. Clinical Indication
A. Prevent or interrupt muscle spasm associated with
Spastic diseases
Spinal cord damage
Overexertion of muscles
B. Adjunct medication for
anesthesia
intubation, surgical and orthopedic procedures

3. Types of Muscle Relaxants
Muscle Relaxants differ by the location and mechanism that muscle contraction is inhibited
Centrally- within the spinal cord
Peripherally- within the muscle

5. Paralysis Spastic – upper motor neuron lesion
Can use central or peripheral relaxer
Stroke
Brain trauma
Multiple sclerosis
Spinal cord transection
Flaccid – lower motor neuron lesion
 atrophy

6. Peripherally Acting Muscle Relaxants
Mechanism of Action
Peripherally acting muscle relaxants interact with nicotinic-muscle (Nm) receptors to
block acetylcholine (ACH) attachment on the receptors nondepolarizing blockers curare, gallamine, pancuronium OR
• stimulate the receptor followed by inability of the receptor to respond to ACH depolarizing blockers succinylcholine

7. Neuromuscular blockers - uses
Any situation where impaired relaxation interferes with function
Before surgery
Allows intubation
Relax abdominal muscles
Orthopedic procedures
fibromyalgia

8. NMJ blockers Tubocurarin (Curare) – arrow poison
Nondepolorizing-lasts min – releases histamine – not in asthma
Pancuronium (Pavulon) – nondepolorizing does not release histamine
Nondepolorizing blockers – competitive – reversed by prostigmine
Succinylcholine (Anectine) depolarizing – rare pseudocholinesterase deficiency

9. Peripherally Acting Muscle Relaxants
Mechanism of Action (continued) OR
The muscle relaxant may interact with
the biochemical pathway within contractile proteins that make up the muscle fibers direct acting skeletal muscle relaxant
dantrolene
Used in MS, cerebral palsy and cord injury

10. Other Effects
Cardiovascular blockade of ACH vagolytic increase heart rate (tachycardia) histamine release or decreased sympathetic tone
vasodilation
Respiratory histamine release
bronchospasm increase in bronchial secretions

11. Cautions, Toxicity, and Drug Interactions
All peripheral muscle relaxants
Paralysis of respiratory muscles
Succinylcholine
Enhanced relaxation in Myasthenia Gravis, spinal cord lesions, ACHesterase inhibitors
Malignant hyperthermia Dantrolene
Hepatotoxicity elevated serum liver enzymes
Peripheral and Central muscle relaxants
Potential muscle relaxation- CNS depressants- alcohol, sedatives, tranquilizers

12. Central Skeletal Muscle Relaxants
Mechanism of Action
Centrally acting muscle relaxants
inhibit reflexes within the spinal cord chlordiazepoxide, diazepam
inhibit gamma-aminobutyric acid (GABA) receptors baclofen
inhibit alpha-2-adrenergic receptors in the CNS tizanidine

13. Central muscle relaxents
Used – chronic spasticity, overexertion, muscle trauma – sprains and strains, nervous tension
Cyclobenzaprine (Flexeril)
Diazepam (Valium)
Methocarbamol (Robaxin)
Often used with aspirin or anti-inflammatory drug

14. Other Effects
CNS blurred vision, dizziness, lethargy, decreased mental alertness
Vascular-decreased sympathetic tone vasodilation, orthostatic hypotension
Dependence with prolonged use

15. Drug Interactions Neuromuscular blocking drugs
Potentiate muscle relaxation- antibiotics, antiarrhythmic drugs, general anesthetics
Potentiate potassium loss- diuretics, digitalis