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Neuromuscular-blocking drugs Martínková 2005

Neuromuscular-blocking drugs Martínková 2005. Events and sites of drug action at a nicotinic cholinergic synapse. Presynaptic nicotinic ACh receptor. Drugs can block neuromuscular transmission: either acting presynaptically to inhibit ACH synthesis or release

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Neuromuscular-blocking drugs Martínková 2005

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  1. Neuromuscular-blocking drugs Martínková 2005

  2. Events and sites of drug action at a nicotinic cholinergic synapse. Presynaptic nicotinic ACh receptor

  3. Drugs can block neuromuscular transmission: • either acting presynaptically • to inhibit ACH synthesis or release • or by acting postsynaptically • interfering with the postsynaptic action of ACH • Presynaptically acting agents: inhibit Ca2+ entry and inhibit ACH release- aminoglycoside antibiotics • Postsynaptically acting agents: • They fall into two categories: • non-depolarising blocking agents -ACH antagonists • depolarising blocking agents - ACH agonists

  4. non-depolarising blocking agents -ACH antagonists • act as competitive antagonists at the N-receptors of the endplate motor paralysis: • extrinsic eye muscles (double vision) • small muscles of the face, limbs and pharynx • (causing difficulty in swallowing) • respiratory muscles • (are the last to be affected and the first to recover) • Used i.v. to produce muscle relaxation but differ in their rates of onset and recovery

  5. Characteristics of neuromuscular-blocking drugs Drug Duration of action Adverse reactions

  6. Non-depolarising block is reversible by anticholinesterase drugs depolarising block is not.

  7. . depolarising blocking agents -ACH agonists Adverse reactions Suxamethonium short acting bradycardia (muscarinic agonist (10 min) effect) -increase in plasma K+concentration (a net loss of K+ from muscles) -increase in intraocular pressure Paralysis is preceded by transient muscle fasciculation (muscle pain) Short duration owing to hydrolysis by plasma CHE (prolonged action in patients with genetic deficiency of plasma CHE)

  8. Usage: Neuromuscular block is used only as an adjunct to anesthesia, when artificial ventilation is available.

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