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CHAPTER 9
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CHAPTER 9

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  1. 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

  4. 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

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

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

  7. NMJ blockers • Tubocurarin (Curare) – arrow poison • Nondepolorizing-lasts 20-30 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

  8. 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

  9. 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

  10. 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 hyperthermiaDantrolene Hepatotoxicity elevated serum liver enzymes Peripheral and Central muscle relaxants Potential muscle relaxation- CNS depressants- alcohol, sedatives, tranquilizers

  11. 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

  12. 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

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

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