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Skeletal muscle relaxants
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Transcript of Skeletal muscle relaxants
Skeletal Muscle Relaxants
18th April, 2013
Classification I
• Centrally acting• Baclofen • Diazepam
• Direct acting• Dantrolene
Classification II
• Peripherally acting (Neuromuscular blockers)– Presynaptic neuromuscular blockers• Inhibit Ach synthesis
– Triethylcholine – Hemicholinium
• Inhibit Ach release – Mg– Aminoglycosides– Botulinum toxin
Classification III
– Postsynaptic neuromuscular blockers• Competitive (non depolarizing blockers)
– Long acting» Pancuronium
– Intermediate acting» Atracurium» Vecuronium» Rocuronium» Cisatracurium
– Short acting» Mivacurium
• Depolarizing blockers » Succinylcholine
Nicotinic ACh Receptor
NMJ
Pharmacodynamics
Non-depolarizing
• Important Features– Nicotinic antagonists– Reversibility with Ach E Inhibitors (↑conc. of ACh)– Cause progressive paralysis (face, eye, fingers, limbs, neck,
trunk muscles, intercostal, diaphragm)– No effects on heart , smooth muscles, or CNS– D-Tubocurarine is the prototypical drug– Polar compounds – Orally inactive ~ so taken parenterally – Don’t cross placenta or CNS
Non-depolarizing Specific Drugs I
• Gallamine– Less potent than curare– Tachycardia
• d –Tubocurarine– 1-2hr duration of action– Histamine releaser (Bronchospasm, Hypotension)– Blocks autonomic ganglia (Hypotension)
• Atracurium– Rapid recovery– Safe in hepatic & renal impairment– Spontaneous inactivation to laudanosine (seizures)
Non-depolarizing Specific Drugs II
• Mivacurium– Metabolized by pseudocholinesterases– Fast onset and short duration
• Pencuronium– Long duration of action– Tachycardia (Anti M, ↑NE release)
• Vecuronium– Intermediate duration of action– Fewer side effects (no histamine release, no ganglion
blockade, no antimuscarinic action)
Depolarizing Neuromuscular Blockers : Dynamics
• Phase I ( Depolarizing )– Binds with nicotinic receptors →depolarization of motor end
plate → initial muscle twitching → Persistent depolarization→ paralysis.
– Phase I block is augmented not reversed by anticholinestrases.
• Phase II ( Desensitization Block )– Continuous exposure to succinylcholine → depolarization
decreases and the membrane become repolarized, but the membrane cannot be depolarized by Ach as long as succinylcholine present → desensitization of the membrane.
Succinylcholine
• Rapid onset/Short duration ~ hydrolyzed by psuedocholinesterases
• Cause Hyperkalemia, Malignant Hyperthermia, bradycardia, ↑intraocular pressure
Therapeutic Uses
• Control convulsion electroshock therapy in psychotic patient .
• Relieve of tetanus and epileptic convulsion.• facilitate endoscopy• As adjuvant in general anesthesia to induce
muscle relaxation• Orthopedic surgery.
Centrally Acting
• Baclofen– GABAB agonist
• Diazepam• Dantrolene
• It interferes with the release of calcium from its stores in sk. muscles (sarcoplasmic reticulum).• It inhibits excitation-contraction coupling in the muscle
fiber.• Used in malignant hyperthermia & spastic states.
Uses of Spasmolytics
• Reduce muscle spasm in – Spinal cord injury– Stroke– Cerebral palsy