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SKELETAL MUSCLE RELAXANTS

SKELETAL MUSCLE RELAXANTS. Skeletal muscle relaxants. Types of Skeletal muscle relaxants: Competitive (Non-depolarizing) Non-competitive (Depolarizing) Directly acting Muscle relaxants Centrally Acting Muscle relaxants Miscellaneous : Aminoglycosides. Skeletal muscle relaxants.

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SKELETAL MUSCLE RELAXANTS

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  1. SKELETAL MUSCLE RELAXANTS

  2. Skeletal muscle relaxants • Types of Skeletal muscle relaxants: • Competitive (Non-depolarizing) • Non-competitive (Depolarizing) • Directly acting Muscle relaxants • Centrally Acting Muscle relaxants • Miscellaneous : Aminoglycosides

  3. Skeletal muscle relaxants Neuromuscular blockers • Non - depolarizing ( competitive )Long acting : Pancuronium, Pipecuronium, Intermediate : Vecuronium, Rocuronium, Atracurium Short acting : Mivacurium • Depolarizing blockers : (Non-competitive) Succinylcholine

  4. Skeletal muscle relaxants • Directly acting Muscle relaxants Dantrolene • Centrally Acting Muscle relaxants Diazepam, Baclofen, Chloroxazone, Tizanidine

  5. Skeletal muscle relaxants Pharmacokinetics : • Most peripheral NM blockers are quaternary compounds – not absorbed orally. • Administered intravenously. • Do not cross blood brain barrier or placenta • SCh is metabolized by Pseudocholinesterase. • Atracurium is inactivated in plasma by spontaneous non-enzymatic degradation (Hoffman elimination).

  6. Mechanism of Action of Non-depolarizing Neuromuscular Blocking Drugs

  7. Non-depolarizing (competitive). • Prototype of Non-depolarizing is tubocurarine • (new generation: pancuronium and gallamine). • Mechanism of Action: In small clinical doses they act the predominantly at the nicotinic receptor site to block ACh. • Because of the competitive nature of the postsynaptic blockade, transient relief of the block can be achieved by increasing ACh levels at the synaptic cleft (i.e. use cholinesterase inhibitors).

  8. Nondepolarizing Agents • Pharmacokinetics:Must be given by injection because they are poorly absorbed orally. Do not cross the BBB. Generally excreted unchanged (i.e. not metabolized). • Therapeutic Use: Adjuvant drugs in surgical anesthesia • Adverse Effects: • Tubocurarine causes release of histamine from mast cells – decrease in blood pressure, bronchospasms, skin wheals. Newer generation don’t. • Decreases tone & motility of GIT Constipation • Hypoxia & Respiratory paralysis

  9. Depolarizing Agents • Prototype of depolarizing agent is succinylcholine (only depolarizing drug in clinical use). • Mechanism of Action: Similar action to ACh, but longer acting. • Phase 1: Membrane is depolarized by opening AChR channels causing brief period of muscle fasciculation. • Phase II: End-plate eventually repolarizes, but because succinycholine is not metabolized like ACh it continues to occupy the AChRs to “desensitize” the end-plate.

  10. Depolarizing Agents • Therapeutic Use: Adjuvant drugs in surgical anesthesia tetanus ECT Status Epilepticus • Pharmacokinetics: Duration of action is short (several minutes) because it is rapidly broken down by plasma cholinesterases (must be administered by continuous infusion) • Adverse Effects: • Hyperkalemia • Muscle soreness • Prolonged apnea • malignant hyperthermia. Treatment: rapid cooling of the body and dantrolene

  11. Skeletal muscle relaxants Directly acting muscle relaxants : Dantrolene : Depolarization triggered release of calcium from the sarcoplasmic contraction is blocked / reduced. • Dantrolene is used orally/ i.v to reduces spasticity in hemiplegia and cerebral palsy. • It is the drug of choice – malignant hyperthermia

  12. Glaucoma

  13. Glaucoma Glaucoma is increased intraocular pressure. Intraocular pressure is determined by the balance between fluid input & drainage out of the globe----- aqueous humor produced by ciliary epitheliumand drained at the filtration angleof the anterior chamber. Objective of glaucoma therapy : --- increase outflow& ordecrease production of aqueous humor.

  14. Glaucoma Major route of aqueous humor drainage is ~ 90% through trabecular route ~ 10% passes through within the ciliary muscle into episceral vessels (uveosceral flow)

  15. Drugs for glaucoma Beta blockers Alpha agonist CA inhibitor Pilocarpine PG analog

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