Skeletal muscle relaxants

Pharmacology PPT

1. Skeletal muscle relaxants Dr Chintan Doshi

2. Neuromuscular blockers Directly acting Surgery - In conjunction with GA Painful muscle conditions Spastic neurological conditions

3. Succinylcholine Long acting: d- Tubocurarine , Pancuronium , Doxacurium , Pipecuronium Intermediate acting: Vecuronium , Atracurium , Cisatracurium , Rocuronium , Rapacuronium Short acting : Mivacurium

4. Competitive neuromuscular blockers (d-TC) Mechanism of action Muscle – flaccid paralysis, diaphragm affected last Autonomic ganglia- d-TC: blocked- Histamine release – d-TC, miva , hypotension, bronchospasm CVS- fall in BP ganglionic blockade histamine release Decrease venous return (paralysis of muscle) HR- increase : vagal ganglionic blockade Atra , cisatra - hofmann elimination Block is reversed by Anti- ChEase

5. Succinylcholine Mechanism of action Muscle – initial fasciculations followed by flaccid paralysis Block is not reversed by Anti- ChEase Metabolized by plasma Pseudocholinesterase - short acting (5-8 min) ADR Muscle soreness, Hyperkalemia Increase IOP, ICP, IAP Cardiac arrhythmia Malignant hyperthermia i.v dantrolene Prolonged apnea Mechanical ventilation FFP

6. Advantages of newer neuromuscular blockers over the older ones No or minimal ganglionic , cardiac or vascular effects No or minimal histamine release Many a short acting: easy reversal Some are rapid acting: provide alternative to SCh without the attendant complications.

7. Uses 1) As an adjuvant to General Anaesthesia D uring abdominal or thoracic surgery , for endotracheal intubation To counteract laryngospasm during Barbiturate anaesthesia To prevent reflex muscle contraction during surgery Selection of drug: onset of action, duration of blockade required, on patient’s hepatic, renal and haemodynamic status. Example; SCh or Mivacurium : employed for brief procedure ( endotrachea intubation, laryngoscopy bronchoscopy )

8. For longer duration suegery : Pipecurinium or Doxacurium can be employed Renal or hepatic insufficiency: Atracurium or Cis - atracurium (inactivated in plasma by Hoffmann degradation) 2) To control Ventilation Ventilatory support - facilitated by continuous infusion of subanaesthetic does of competitive neuromuscular blocker which reduce the chest wall resistance to inflation

9. 3) to prevent Trauma during electroconvulsive therapy SCh with Diazepam: prevent injuries or fracture due to excessive convulsion from ECT Mivacurium : alternative 4) Sever case of tetanus and status epilepticus (not controlled Diazepam): paralysed by repeated dose of a competitive blocker and maintained on intermittent positive pressure respiration till disease subsides

10. CENTRALLY ACTING MUSCLE RELAXANTS ( spasmolytics )

11. Dantrolene Mechanism of action RyR1 ( Ryanodine Receptor) calcium channels in the sarcoplasmic reticulum of skeletal muscles and prevents Ca2+ induced Ca2+ release through these channels Dose: 25–100 mg QID

12. Contd. Uses reduces spasticity in upper motor neurone disorders , hemiplegia , paraplegia, cerebral palsy malignant hyperthermia:Used i.v Adverse effects Muscular weakness Sedation, malaise, light headedness Diarrhoea Long term use:Liver toxicity

13. Use of centrally acting muscle relaxant 1) Acute muscles spasms Overstretching of a muscle , sprain , tearing o f ligaments and tendons, painful spasm of muscles , dislocation , rheumatic disorders Mephenesin like and BZD muscle relaxants + analgesics : commonly used 2) Torticolis , lumbago, backache, neuralgias Painful spasm of certain muscles : prominent feature R espond in the same way as acute muscle spasms.

14. 3) Anxiety and tension A ssociated with ↑ tone of muscles . Diazepam group of drugs and chlormezanone benefit by their antianxiety as well as muscle relaxant actions . 4) Spastic neurological diseases Impairment of descending pathways in the cerebrospinal axis and withdrawal of inhibitory influence over the stretch reflex chronic ↑ in muscle tone or spasticity. Baclofen , D iazepam , Tizanidine and D antrolene

15. 5) tetanus Diazepam- infu sed i.v. and dose is titrated by the response Methocarbamol : alternative 6) Electroconvulsive therapy Diazepam ↓ the intensity of convulsion resulting from ECT SCh : used in addition for total suppression of the muscular component of ECT 7) Orthopedic manipulations P erformed under the influence of diazepam or methocarbamol given i.v.

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