Classification of Skeletal Muscle Relaxants

1. Muscle Relaxants
Presented By:- Dr. Nilofar Rasheed(PT)
MPT (Ortho)
Asst. Professor
Noida International University

2. Muscle Relaxants: -
• Muscle relaxants are used to relieve muscle spasms which may
result form some conditions which affect the nervous system.
• Skeletal muscles attach to the bones and are used for voluntarily
movements of the body. Muscle spasms occur when a
skeletal muscle contracts and does not relax. Muscle spasms are
forceful and involuntary. A sustained muscle spasm is called
a muscle cramp.
• Medication helps the muscles to relax, which may also
reduce pain and discomfort.

3. Muscle relaxants
Affects skeletal muscle function
Decrease the muscle tone.
used to improve symptoms such as muscle
spasms, pain and hyperreflexia.

4. Skeletal Muscle Relaxants: -
Skeletal muscle relaxants are drugs that act
peripherally at neuromuscular junction/
muscle fiber itself of centrally in the
cerebrospinal axis to reduce muscle tone and /
or cause paralysis.

6. Nondepolarizing (Competitive) blockers: -
Mechanism of Action: - The site of action of both
competitive and depolarizing blockers is the end plate of
Skeletal muscle fibers.
Non depolarizing Blockers
Bind with Ach receptor(Acetylcholine)
Produces ganglionic receptor
Blocks neuro muscular transmission
Hence. Decreases tone of muscle
Paralysis/ relaxation of muscle

7.  Uses
 Facilitate the surgery especially intra abdominal, intra
thoracic surgeries.
 Prolonged ventilation.
 Endo tracheal intubation.
 Adverse effects.
 Apnea
 Muscle pain
 Dizziness.

8. Depolarizing blockers: -
Mechanism Of Action: - Similar action to Ach,
but longer acting.
Depolarizing Blocker
Combine with nicotine receptors
Initial depolarization of motor end plate
Muscle twitching
Persistent depolarization
Relaxation

11. Directly Acting Muscle Relaxants:
-
Dantrolene: -
o It interference with release of Ca+ from it stores in
Sk.Muscles(Sarcoplasmic reticulum)
o Inhibit excitation-contraction coupling.
Uses: -
 UMN disorder
 Hemiplegia
 Paraplegia
 Cerebral Palsy
 Multiple Sclerosis
 Malignant Hyperthermia
 Neuroleptic Malignant syndrome

12. Adverse Effects: -
 Flushing
 Dizziness
 Drowsiness
 Dysphagia
 Muscular weakness
 Sedation
 Malaise
 Diarrhoea
 Liver Toxity

13. Centrally acting Peripherally acting
Decrease muscle tone
without reducing
voluntary power
Cause muscle paralysis,
voluntary movements lost
Selectively inhibit
polysynaptic reflexes in
CNS
Block neuromuscular
transmission
Cause some CNS depression No effect on CNS
Given orally,
sometimes
parenterally
Practically always given i.v.
Used in chronic spastic
conditions,
acute muscle spasms,
tetanus
Used for short-term purposes
(surgical operations)
Comparative features of centrally and
peripherally acting muscle relaxants

14. Class Example
Mephenesin congeners Mephenesin
Carisoprodol
Chlorzoxazone
Chlormezanone
Methocarbamol
Benzodiazepines Diazepam and others
GABA mimetic Baclofen
Thiocolchicoside
Central α2 agonist Tizanidine
Centrally acting muscle
relaxants: -
Classification: -

15. Baclofen- Oral/Intrathecal
GABA agonist at GABA B receptor increase K+
conductance Hyperpolarization of membrane SK.
Mus. Relaxation
• Also(-) release of substance P
• Uses
• severe spasticity
• Pain like multiple sclerosis
• Pain like ALS (amyotropic lateral sclerosis)
• spinal injuries

16. Adverse effect: -
 Drowsiness
 Confusion
 Seizure
 Respiratory depression
 Comma
 Mental confusion
 Weakness and ataxia
 Serum transaminases may rise
 Sudden withdrawal after chronic use may cause
hallucinations
 tachycardia and seizures.

17. e.g;Tizanidine: -
Centrally acting
Mechanism Of Action: -
Centrally acting Alpha 2 adrenergic agonist
Inhibits release of excitatory amino acids in the Spinal
interneurons.
It re- in forces both pre- synaptic & Post- synaptic
inhibition in the cord
• It may facilitate the inhibitory transmitter glycine as
well.

18.  Acute muscle spasms
 Torticollis
 Lumbago
 Backache
 Neuralgias
 Anxiety and tension
 Spastic neurological diseases
 Tetanus
 Electroconvulsive therapy
 Orthopedic manipulations
Therapeutic Usages: -

19. Adverse effect: -
 Drowsiness
 Hypotension
 Dry Mouth
 Asthenia
 Night-time insomnia
 Hallucinations.
 Dose- dependent elevation of liver enzymes occurs.
 Though no consistent effect on BP has been
observed
 It should be avoided in patients receiving
antihypertensive, especially clonidine.