lecture 13- Skeletal muscle relaxants.ppt
- 2. Skeletal muscle relaxants Are drugs used to induce skeletal muscle relaxation.
- 3. Classification of SKM relaxants 1. Peripherally acting skeletal muscle relaxants 2. Centrally acting skeletal muscle relaxants e.g. Baclofen – Diazepam 3. Direct acting skeletal muscle relaxants e.g. Dantrolene
- 4. 1- Peripherally acting SKM relaxants (Neuromuscular blockers) Neuromuscular blockers act by blocking neuromuscular junction or motor end plate leading to skeletal muscle relaxation.
- 5. Classification of Peripherally SKM relaxants According to mechanism of action, they are classified into: 1. Competitive neuromuscular blockers 2. Depolarizing neuromuscular blockers
- 6. I) Competitive neuromuscular blockers Mechanism of action: Compete with Ach for the nicotinic receptors present in post junctional membrane of neuromuscular junction or motor end plate. No depolarization of post junctional membrane (non depolarizing). Action can be reversed by increasing Ach concentration.
- 7. Competitive neuromuscular blockers have the common suffix curium or curonium Classified according to duration of action into: Atracurium Mivacurium Pancuronium Vecuronium
- 8. Long acting ◦ d-tubocurarine ◦ Pancuronium Intermediate acting ◦ Atracurium Vecuronium Short acting ◦ Mivacurium
- 9. Pharmacokinetics of competitive neuromuscular blockers They are polar compounds Inactive orally & taken parenterally Do not cross BBB (no central action) Do not cross placenta Metabolism depend upon kidney or liver Except Mivacurium degraded by acetyl cholinesterase Atracurium spontaneous degradation in blood
- 10. Pharmacological actions of competitive NMBs: Skeletal muscle relaxation. - Small rapidly contracting muscles of face, eyes, fingers, neck , trunk muscle ,intercostal muscles and diaphragm - Recovery comes from REVERSE MANNER starting with diaphragm, last is face and eyes
- 11. Pharmacological actions of competitive NMBs: They produce different effects on CVS Some release histamine and produce hypotension o d-Tubocurarine o Atracurium o Mivacurium Others produce tachycardia (with increase H.R) o Pancuronium
- 12. 1- d – Tubocurarine Long duration of action (1 - 2 h) Eliminated by kidney 60% - liver 40%. Not used clinically due to adverse effects: Histamine releaser leading to Bronchospasm (constriction of bronchial smooth muscles). Hypotension Tachycardia More safer derivatives are now available
- 13. 2- Atracurium Has intermediate duration of action (30 min). Liberate histamine leads to transient hypotension Eliminated by non enzymatic chemical degradation in plasma (hydrolysis at body pH). Used in liver failure & kidney failure (drug of choice). Should be avoided in asthmatic patients
- 14. 3- Mivacurium Chemically related to atracurium Fast onset of action Has the shortest duration of action (15 min) of all competitive neuromuscular blockers. Metabolized by pseudo-cholinesterase. Longer duration in patient with liver disease or genetic cholinesterase deficiency or malnutrition. Transient hypotension (due to histamine release).
- 15. 4- Pancuronium Excreted by the kidney ( 80 % ). Long duration of action. Side effects: Hypertension, tachycardia It increase norepinephrine release from adrenergic nerve endings Antimuscarinic action (block parasympathetic action). ◦It is avoid in patient with coronary diseases.
- 16. 5-Vecuronium More potent than tubocurarine (6 times). Metabolized mainly by liver and excreted in bile. Intermediate duration of action. Advantages No histamine release. No tachycardia.
- 17. II) Depolarizing Neuromuscular Blockers Mechanism of action They combine with nicotinic receptors in post- junctional membrane of neuromuscular junction leads to initial depolarization of motor end plate leads to muscle twitching leads to persistent depolarization leads to Skeletal muscle relaxation
- 18. 1- Succinylcholine (suxamethonium) It acts on skeletal muscles by twitching cause relaxation Pharmacokinetics Fast onset of action (1 min.). Short duration of action (5-10 min.). Metabolized by pseudo-cholinesterase in plasma Half life is prolonged in ◦ Neonates ◦ Elderly ◦ Pseudo-cholinesterase deficiency (liver disease or malnutrition or genetic cholinesterase deficiency).
- 19. Side Effects Hyperkalemia (Cardiac arrest) CVS arrhythmia Increase intraocular pressure contraindicated in glaucoma Can produce malignant hyperthermia May cause succinylcholine apnea due to deficiency of pseudo-cholinesterase.
- 20. It is a rare inherited condition that occurs upon administration of drugs as: ◦ General anesthesia e.g. halothane ◦ Neuromuscular blockers e.g. succinylcholine Occur in some patients due to genetic defect. Malignant Hyperthermia cause increase Ca release, muscular rigidity, metabolic acidosis, tachycardia, and hyperpyrexia
- 21. Notes Side effects Duration Drug # Renal failure Hypotension Long 1-2 h Tubocurarine # Renal failure Tachycardia Long 1-2 h Pancuronium Spontaneous degradation Used in liver and kidney failure Transient hypotension Histamine release Short 30 min. Atracurium # Liver failure Few side effects Short 40 min. Vecuronium Metabolized by pseudocholinesterase # Choline esterase deficiency Similar to atracurium Short 15 min. Mivacurium # CVS Diseases # Glaucoma # Liver disease Hyperkalemia Arrhythmia Increase IOP Short 10 min. Succinyl choline
- 22. Uses of neuromuscular blockers Control convulsion of electroshock therapy in psychotic patients. Relieve of tetanus and epileptic convulsion. As adjuvant in general anesthesia to induce muscle relaxation Facilitate endotracheal intubation Orthopedic surgery.
- 23. Drugs and diseases that modify effects of neuromuscular blockers Myasthenia gravis increase the response to muscle relaxants. Drugs as aminoglycosides (e.g. streptomycin), magnesium sulphate, general anesthetics can potentiate or enhance the effect of neuromuscular blockers.
- 24. Spasmolytics They reduce muscle spasm in spastic states Baclofen: Centrally acting GABA agonist – acts on spinal cord. Diazepam (Benzodiazepines): Centrally acting Facilitate GABA action on CNS. Dantrolene: Direct action on skeletal muscles.
- 25. Uses of spasmolytics They reduce muscle spasm in spastic states produced by neurological disorders as: • Spinal cord injury • Cerebral stroke • Cerebral palsy
- 26. Dantrolene Mechanism of action Acts directly on skeletal muscles. It interferes with the release of calcium from its stores in skeletal muscles. It inhibits excitation-contraction coupling in the muscle fiber. Orally, IV, (t ½ = 8 - 9 h). Used in the treatment of: Spastic states Malignant hyperthermia