Muscle relaxants ●cause relaxation of striated (voluntary skeletal) musculature (in contrast to spasmolytics which relax unstriped musculature) Classification of myorelaxants 1. Neuromuscular blocking drugs = periferial (direct) myorelaxants ●interact with acetylcholine nicotinic (N) receptors of skeletal musculature a) stabilizing myorelaxants – N-receptors antagonists b) depolarizing myorelaxants – N-receptors agonists ●continuous N-receptors stimulation ⇒ depolarization of cells ⇒ functional antagonism: further leading of impulses imposible, no muscle contraction c) indirect myorelaxants: botulin ●irreversibly inhibits acetycholine releasing 2. Central muscle relaxants ●acts in CNS ●structurally heterogenic group ●compounds with various mechanisms of action Stabilizing myorelaxants ●N-receptors antagonists in skeletal muscle cells ●usage: surgical operative measures (often as a part of some form of anaesthesia) ●structures derived from curare alkaloids Curare: arrow poison of South American Indians ●preparation from various plants ●contained a complex mixture of alkaloids Curare classification: according to preparation and package in which it was shipped to Europe 1. Tubocurare: in hollow bamboo rods 2. Calebase curare: in bottle-shaped cucurbits (gourds, calabashes - from plants of genus Strychnos) 3. Pot curare: in ceramic vessels Structural types: 1. Benzyltetrahydroisoquinolines: tubocurarine (from tubocurare) atracurium besylate (synthetic) mivacurium besylate (synthetic) etc. 2. Indole derivatives: toxiferine C alcuronium chloride 3. Steroids with basic substituents: vecuronium bromide pancuronium bromide rocuronium bromide 1. Benzyltetrahydroisoquinolines H3C O H C O O CH3 3 H3C H + H3C H C O O H3C N O 3 OH H C 3 O O H3C H H H + CH + N 3 O O N O OH CH3 N CH3 O O O H3C O CH3 O CH3 tubocurarine atracurium ●used as besylate Tracrium ® inj. sol. 1. Benzyltetrahydroisoquinolines (continued) H C H C 3 O 3 O H3C O O O H3C O H O + H3C + H N CH3 N CH3 CH3 O O O CH3 O O CH3 O CH3 O CH3 mivacurium ●used as besylate Mivacron ® inj. sol. 2. Indole derivatives R OH + N O O H H H H N N H H H N H H H H N + N R HO ●for comparison: strychnine R = -CH toxiferine C 3 ●from Strychnos nux vomica ●natural ●in small amounts as central R = -CH CH=CH alcuronium 2 2 analeptic (obsolete) ●as chloride Stereochemistry: „playing cards symmetry“ toxiferin C alcuronium chloride ●structure similarity with strychnine, both indole alcaloids ●dimer ●2x pentacyclic system ●2 quarternary ammonium moieties Stereochemistry: ●chiral ●contain C2 symmetry axis: „playing cards symmetry“ Effects of alcuronium chloride ●more active than tubocurarine ●relatively short time of action ●not absorbed from GIT ●very stable, excreted in unchanged form Preparation: ●partial synthesis from strychnine 3. Steroids with basic substituents O H CH H C O 3 CH 3 O 3 H3C H H + CH3 H O + N CH3 + N O N H3C H H H C H H 3 CH3 H H N H3C O H H H H H H3C O H O vecuronium pancuronium Norcuron ® inj. Pavulon ® inj. sol. ●as bromides 3. Steroids with basic substituents (continued) H3C H3C H3C + H CH3 O N H3C O O CH3 H + H N H C O N 3 H H3C H O N H C H + O N 3 H H N CH3 H H H H H2C O H CH3 H H HO H rocuronium pipecuronium Esmeron ® inj. sol. Arduan ® inj. sicc. + solv. ●facilitation of tracheal intubation Depolarizing myorelaxants ●agonist of N-receptor ●continuous depolarization leads to muscules slack Usage: introduction into general anaesthesia (intubation) Compounds: synthetic bis-quarternary ammonium salts ●originated by simplifying of tubocurarine structure H C 3 CH H3C + 3 O + N O N H C CH CH H3C 3 3 H3C 3 + + CH3 N N - - CH X H C CH3 3 X 3 - - X O X O dekamethonium (halide) suxamethonium (halide) ●non-hydrolyzable syn. succinylcholine (halide) ●comparatively toxic ●hydrolyzable ●long effect ●fast cleft by esterases ⇒ short effect Succinylcholinjodid Valeant ® inj. plv. sol. Comparison of molecule sizes of direct muscule relaxants Indirect myorelaxants Botuline ●protein with M about 150, 000 r ●product of anaerobic bacterium Clostridium botulinum (serotypes A – G: A – Botox infusion; B - Neurobloc infusion) ●extremely toxic (food poisoning, potetial biological weapons) Indications: cervical dystonia, facial spasms, scrivener's palsy and other spasms ●in cosmetics for smoothing of wrinkles – very hazardous ●irreversibly inhibits acetylcholin release ●local injection into the particular muscle ●blocks transfer of impulse by means of acetylcholine to the muscle ●muscle paralysis ●to hands of qualified physicians only ●by no means can reach bloodstream ●new injection is possible after 3 – 4 months (the effect is poorly estimable in shorter intervals due to possible formation of antibodies) Central muscle relaxants (myotonolytics) Using: painful spasms of skeletal muscles (not in surgical measures) Structures: heterogenic group Mechanisms of action: various, not perfectly known in every case ●im most they act sedatively in high doses Central muscle relaxants (myotonolytics) Carbamates derived from diols CH3 CH3 CH3 O O O NH O O O O CH3 H2N NH2 H2N O CH3 H3C meprobamate carisoprodol ●myorelaxant, sedative, anxiolytic ●effectiveness unsure Cl NH2 O H OH baclophene ●GABA derivative ●GABA receptor agonist B ●blocks voltage-gated input of Ca2+ into CNS neurons Usage: spasmodic conditions (sclerosis multiplex, cramps in crucial region etc.) O - + O N NH N Cl NH O N S N N N thizanidine O ●myorelaxant, analgesic, antihypertensive N ●probably α receptors agonist O H 2 ●blocks release of excitation dantrolene transmitters (glutamate, ●hydantoine derivative aspartate) ●myorelaxant ●usage: eg. sclerosis ●Mode of action: directly to skeletal multiplex, ischias 2+ muscles; lowers Ca release .