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Neuromuscular blocking agents

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Neuromuscular blocking agents

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Neuromuscular blocking agents

  1. 1. NEUROMUSCULAR BLOCKING AGENTS PRESENTED BY: DR.JAGADISH JENA DEPT.OF ANAEST.& CR.CARE VIMSAR,BURLA
  2. 2. HISTORY
  3. 3. Definition: NMBA are the drugs that act peripherally at NM-Junction and muscle fiber itself to block neuromuscular transmission. Why do we need them ? In order to facilitate muscle relaxation for surgery and mechanical ventilation during surgery & in ICU.
  4. 4. Neuromuscular junction • Association between a motor neuron and a muscle cell. • Synaptic cleft.:Synaptic cleft.:The cell membranes of the neuron and muscle fiber are separated by a narrow (20-nm) gap. • The neurotransmitter responsible for neurotransmission at the neuromuscular junction is acetylcholine. • It is synthesized in the cytoplasm by combination of choline and coenzyme A with the help of choline acetyl transferase. • These synthesized acetylcholine stored in vesicles. • A single vesicle contains about a quantum of Ach .
  5. 5. • As a nerve’s action potential depolarizes its terminal, an influx of calcium ions through voltage-gated calcium channels into the nerve cytoplasm allows storage vesicles to fuse with the terminal plasma membrane and release their contents. • The ACh molecules diffuse across the synaptic cleft to bind with nicotinic cholinergic receptors on a specialized portion of the muscle membrane at the motor end-plate. • Each neuromuscular junction contains approximately 5 million of these receptors. • Among these minimum 500000 receptors required to be activated for normal muscle contraction.
  6. 6. Structure of ACh receptors • Each ACh receptor in the neuromuscular junction normally consists of five protein subunits; two α subunits; and single β, δ, and ε subunits. • Only the two identical α subunits are capable of binding Ach molecules. • If both binding sites are occupied by ACh, a conformational change in the subunits, briefly (1 ms) opens an ion channel in the core of the receptor. • The channel will not open if Ach binds on only one site.
  7. 7. • Another isoform of Ach contains a γ subunit instead of the ε subunit known as fetal or imature receptor,because this form initially expressed in fetal muscle. • It is also often referred to as extrajunctional receptors.  Cations flow through the open ACh receptor channel (sodium and calcium in; potassium out), generating an end-plate potential . • When enough receptors are occupied by ACh, the end- plate potential will be sufficiently strong to depolarize the perijunctional membrane.
  8. 8. • Sodium channels are present in muscle membrane. • Perijunctional areas of muscle membrane have a higher density of these sodium channels than other parts of the membrane. • These sodium channels have two types of gate - voltage dependent - time dependent • Sodium ions pass only when both gates are open.
  9. 9.  sodium channesodium channel is a transmembrane protein that can be conceptualized as having two gates.two gates.  Sodium ions pass only when both gates are open.  Opening of the gates isOpening of the gates is time dependent andtime dependent and voltage dependentvoltage dependent.  The channel therefore possesses threethree functional states.functional states.  A...At rest.At rest, the lower gate is open but the upper gate is closed  B...reaches threshold voltage depolarization,depolarization, the upper gate opens and sodium can pass  C...Shortly after the upper gate opens the timedependent lowertimedependent lower gate closesgate closes
  10. 10. • With the opening of sodium channels and entry of sodium,calcium ions release from sarcoplasmic reticulum. • This intracellular calcium allows the contractile proteins actin and myosin to interact, bringing about muscle contraction.
  11. 11. Steps in normal NM transmission.
  12. 12. Classification-mechanism & duration of action Depolarizing Nondepolarizing
  13. 13. MECHANISM OF ACTION of depolarizing NMBA
  14. 14. Phases of block in Depolarizing NMBA
  15. 15. Mechanism of action of non- depolarizing NMBA
  16. 16. OTHER MECHANISMS OF NEUROMUSCULAR BLOCKADE
  17. 17. SEQUENCE OF MUSCLE BLOCKADE • First muscle to be blocked by both depolarising and non depolarizng muscle relaxants are the central muscles then peripheral muscles blocked. • So the sequence of blockade is... FACE – JAW –PHARYNX-LARYNX – RESPIRATORY –TRUNK MUSCLES – LIMB MUSCLES • At recovery these recover in the same order.
  18. 18. Depolarizing NMBA (Suxamethonium)
  19. 19. SUCCINYLCHOLINE
  20. 20. Mechanism of action
  21. 21. Metabolism & Excretion
  22. 22. • However duration of action can be prolonged or prolonged apnea after succinylcholine can occur due to the following conditions: - low pseudocholinesterase - atypical pseudocholinesterase - high dose or phase 2 block - hypothermia
  23. 23. Decreased level of pseudocholinesterase
  24. 24. Atypical/Abnormal pseudocholinesterse
  25. 25. Measurement of Atypical Pseudocholinesterse
  26. 26. Dibucaine Number
  27. 27. Management of succinylcholine Apnoea
  28. 28. Drug interaction special considerations
  29. 29. 2. Nondepolarizing Relaxants
  30. 30. Drug Interactions
  31. 31. Dosage & Storage
  32. 32. Side Effects & Clinical Considerations
  33. 33. 1.Cardiovascular
  34. 34. B. Fasciculations
  35. 35. C. Hyperkalemia
  36. 36. Conditions causing susceptibility to succinylcholine-induced hyperkalemia
  37. 37. Mechanism of hyperkalemia
  38. 38. D. Muscle Pains
  39. 39. E. Intragastric Pressure Elevation
  40. 40. F. Intraocular Pressure Elevation
  41. 41. G. Masseter Muscle Rigidity
  42. 42. H. Malignant Hyperthermia
  43. 43. I. Intracranial Pressure
  44. 44. Nondepolarizing Muscle Relaxants
  45. 45. Classification- Chemistry Gantacurium
  46. 46. Unique Pharmacological Characteristics
  47. 47. A. Suitability for Intubation
  48. 48. Why potent NMBA has slow onset of action? What is priming dose ?
  49. 49. B. Suitability for Preventing Fasciculations
  50. 50. C. Maintenance Relaxation
  51. 51. D. Potentiation by Inhalational Anesthetics
  52. 52. E. Autonomic Side Effects
  53. 53. F. Histamine Release
  54. 54. General Pharmacological Characteristics of Non depolarizing NMBA
  55. 55. A. Temperature • Hypothermia prolongs blockade by • 1.decreasing metabolism • (eg, mivacurium, atracurium, and cisatracurium) and • 2.delaying excretion • (eg, pancuronium and vecuronium).
  56. 56. B. Acid–Base Balance • Respiratory acidosis potentiates the blockade of most nondepolarizing relaxants and antagonizes its reversal.
  57. 57. C. Electrolyte Abnormalities • Hypokalemia and hypocalcemia ....augment a nondepolarizing block. • Hypermagnesemia..... potentiates a nondepolarizing blockade by competing with calcium at the motor end-plate.
  58. 58. D.Drug interactions
  59. 59. F. Concurrent Disease • Neurological or muscular disease can have profound effects on an individual’s response to muscle relaxants. • Cirrhotic liver disease and chronic renal failure increased volume of distribution and a lower plasma concentration for a given dose of water-soluble drugs, such as muscle relaxants • Drugs dependent on hepatic or renal excretion may demonstrate prolonged clearance • So greater initial (loading) dose—but smaller maintenance dose might be required in these patients.
  60. 60. ATRACURIUM • Has a quaternary group. • Benzylisoquinoline structure is responsible for its its unique method of degradaton. • It undergoes hofmann elimination and ester hydrolysis. • Its metabolism is independent of hepatic and renal function.
  61. 61. Dosage & Storage
  62. 62. Side Effects & Clinical Considerations
  63. 63. CISATRACURIUM • It is a stereoisomer of atracurium. • Four times more potent than atracurium. • It undergoes hofmann elimination like atracurium but ester hydrolysis dose not occur. • It dose not produce the histamine and laudanosine production is 5 times lesser than atracurium. • Metabolism and elemination are independent of hepatic and renal failure. • Does not alter heart rate or blood pressure,not alter heart rate or blood pressure, nor does it produce autonomic effects. • Cisatracurium shares with atracurium the… – production of laudanosine,laudanosine, – pH and temperature sensitivitypH and temperature sensitivity & chemical incompatibility.
  64. 64. PANCURONIUM
  65. 65. Side Effects & Clinical Considerations
  66. 66. VECURONIUM
  67. 67. ROCURONIUM
  68. 68. NEWER MUSCLE RELAXANTS
  69. 69. Gantacurium
  70. 70. AV002 (CW002)
  71. 71. OTHER RELAXANTS (Historical interest)
  72. 72. References: • Miller’s anaesthesia(7th edition) • Clinical anaesthesiology(5th edition):Morgan • Essentials of medical Pharmacoly:K.D.Tripathy • Short Text book of anaesthesia: Ajay Yadav • E-Books

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