It is detailed presentation on skeletal muscle relaxants it is more elaborative and detailed version of drugs involved in skeletal Muscle physiology Skeletal muscle relaxants consist of both antispasticity and antispasmodic agents, a distinction prescribers often overlook. The antispasticity agents-baclofen, tizanidine, dantrolene, and diazepam-aid in improving muscle hypertonicity and involuntary jerks

1. Skeletal muscle relaxants

2. Peripherally acting skeletal muscle relaxants
• These drugs act peripherally and block neuromuscular transmission at
neuromuscular junction, causing paralysis and or reduce tone of skeletal
muscle.
• They mainly block Nm receptors. This produces skeletal muscle relaxation.

5. • Mechanism of action: the site of
action of skeletal muscle relaxants
is the motor end plate of the
skeletal muscle fibres

11. Succinylcholine apnoea
• SCh is rapidly hydrolysed by pseudocholinesterase, hence has a very short
duration of action (3–8 minutes).
• Transient apnoea is usually seen at the peak of its action.
• In people with liver disease or atypical pseudocholinesterase due to genetic
defect, the metabolism of SCh becomes slow which results in severe
neuromuscular blockade leading to respiratory paralysis with prolonged
apnoea. This is referred to as ‘prolonged succinylcholine apnoea’.
• Fresh frozen plasma should be infused.
• Patient should be ventilated artificially until full recovery.

12. Uses of peripherally acting skeletal muscle relaxants
• Adjuvants to general anesthesia
• For adequate muscle relaxation
• Abdominal and thoracic surgeries, intubation and endoscopies, orthopaedic
manipulation etc
• Vecuronium,cisatracurium and rocuronium are frequently used.
• Succinylcholine is employed for brief procedures like endotracheal intubation,
oesophagoscopy, reduction of fractures, dislocation to treat laryngospasm
• Ocular surgery( competitive blockade)

13. Drug interactions
• Non depolarising blockers x antibiotics
• General anesthetics x smr
• Thiopentone x sch
• Thiazides x smr

14. • Assisted mechanical ventilation
• To avoid convulsions and coma in
electro convulsive therapy
• Spastic disorders- tetanus and
status epilepticus.

15. Reversal of neuromuscular blockers
• Edrophonium or neostigmine by increasing the concentration of ACh reverses
the effect of d-TC and other competitive blockers at NMJ.
• Use of prior atropine administration is necessary to block the muscarinic
effects of anti- cholinesterases .
• Mivacurium (short acting), atracurium (intermediate acting), etc. do not require
reversal.

16. Centrally acting skeletal muscle relaxants
• Most of the centrally acting skeletal muscle relaxants are available in
combination with one or other nonsteroidal anti-inflammatory drugs (NSAIDs).
• All of them cause certain degree of sedation.
• They act by depressing polysynaptic pathways in spinal and supra- spinal
sites.
• They are used to reduce spasm associated with cerebral palsy, trauma,
sprain, tetanus, multiple sclerosis, etc.

17. Directly acting skeletal muscle relaxant
• Dantrolene. Dantrolene is a directly acting skeletal muscle relaxant.
• It inhibits depolarization-induced Ca2 release from sarcoplasmic reticulum and
produces skeletal muscle relaxation.
• Intravenous dantrolene is the life-saving drug in malignant hyperthermia.
• It is used orally to reduce spasm in multiple sclerosis, cerebral palsy, spinal
injuries, etc. The side effects are drowsiness, diarrhoea, dizziness, headache,
fatigue and rarely hepatotoxicity.

19. Botulinum toxin A
• Botulinum Toxin A. It is obtained from Clostridium botulinum, a gram-positive
anaerobic bacterium.
• The toxin prevents release of ACh into the synaptic cleft by inhibiting proteins
necessary for the release of ACh.
• Thus, it normalizes the tone in hyperreactive or spastic muscles when given
locally.
• It is given intradermally for antiwrinkle effect in cosmetic procedures and into
the muscle in multiple doses for spasticity or dystonia.