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By: Mrs. Kalaivani Sathish, M. Pharm
PIMS - PANIPAT
• SMRs are drugs that reduce the muscle
tone either by acting peripherally at the
neuromuscular junction or centrally in the
cerebrospinal axis or directly on the
contractile mechanism. They reduce the
spasticity in a variety of neurological
conditions and are also useful in surgeries.
• NEUROMUSCULAR BLOCKERS (NMB)
• Competitive Blockers
D – Tubocurarine (d-Tc) is obtained from the
plant Chondrodendrum tomentosum.
It is a quaternary ammonium compounds
because of which they are not well-
absorbed and are quickly excreted.
• Non depolarizing blockers binds to
• Blocks the action of Ach
PHARMACOLOGICAL ACTION OF
• Skeletal muscles: On parenteral administration,
tubocurarine initially causes muscular weakness
followed by flaccid paralysis.
• Autonomic Ganglia: in high doses tubocurarine can
block autonomic ganglia and adrenal medulla and
• Histamine Release – Bronchospasm, ↑ed tracheo
bronchial and gastric secretions occurs due to the
release of histamine. This in turn leads to hypotension.
• Pharmacokinetics – D – Tc is a quaternary
compound, hence not absorbed orally. It is given
in IM or IV.
• Adverse Effects – Respiratory Paralysis,
Prolonged apnea, Hypotension, Flushing and
• Neostigmine is used to treat toxicity as it reverse
the skeletal muscle paralysis and it is the antidote
in Curare poisoning. Anti histamines are given to
counter effect of histamine.
• TREATMENT OF TOXICITY:
• Neostigmine may be used to reverse the skeletal
muscle paralysis and it is the antidote in curare
poisoning .anti histamine give to counter the effect
• Synthetic competitive blocker :
• Pancuronium, vecuronium, atracuronium, have
intermediate onset ( 2 – 4 minutes ) while
rapacuronium and rocuronium have fast onset of
action ( 1 – 2 minutes ) .
• Succinyl choline is a quaternary ammonium
compound with the struture resembling two
molecules of acetyl choline joined together.
• Mechanism of action :
• The neuromusular effects of SCh are like those of
Ach .SCh stimulate the nicitinic receptor and
depolarise the skeletal muscle membrane. But,
unlike Ach succinyl choline is destroyed very
slowly by pseudocholinesterase . Presence of the
drug causes peristant depolarisation resulting
flaccid paralysis .
• Pharmacological action
• skeletal muscle:
• On IV administration onset of action is very rapid –
with in 1 minute.Initial transient muscular
fasciculation and twitching, mostly in the chest
and abdominal regions are followed by skeletal
• Initially hypotension and bradycardia may result
from stimulation of vagal ganglia .this is followed
by hypertension and tachycardia due to
stimulation of sympathetic ganglia.
• Pharmacokinetics :
• SCh is rapidly hydrolysed by
pseudocholinesterase - hence it is short acting
about 5 min.heriditary defect such people ,SCh
does not metabolized even the usual dose result
prolonged apnea and paralysis .Artificial
ventilation and fresh blood transfusion are needed
to supply pseudocholinesterase.
• Adverse effect:
• Post operative muscle pain is acommon AE of SCh
• Hyper kalemia :
• Depolarizing blocker can cause hyperkalemia due
to sudden release of K from thhe intracellular
• Cardiac arrhythmias :
• SCh can cause cardiac arrhythmias.
• Adverse effect:
• Malignant hyperthermia :
• It is a rare genetically determined condition where
there is a sudden↑ in the body temperature and
severe muscle spasm due to release of
intracellular Ca from the sacroplasmic reticulam.
• Drug interaction :
• 1. GA augment the action of SMRs.
• 2.Anticholinesterase like neostigmine reverse the
action of competitive blockers.
• 3.Aminoglycoside and calcium channel blocker
potentiate the action of SMRs.
Drugs acting peripherally at NMJ
1. Adjuvant to anesthesia :
Adequate muscle relaxation is essential during
surgeries.SMR are used as adjuants to GA.
2. In ECT (Electroconvulsive Therapy)
SMR protects the patient from convulsion and
trauma during ECT.
3. In Spastic Disorder: SMR are used to overcome
the spasm of tetanus.
4. In Minor Procedure: SMR are useful in
laryngoscopy, bronchoscopy and esophagoscopy.
Drugs acting peripherally at NMJ
5. Status Epilepticus – Used with anticonvulsant
6. Ventilators: SMR are used to enhance artificial
CENTRALLY ACTING MUSCLE RELAXANTS
These drugs acts on higher centre and cause muscle
relaxation without loss of consciousness. They also have
CENTRALLY ACTING MUSCLE
MEChANISM of ACTIoN
Depress the polysynaptic reflexes (This reflex
maintains muscle tone)
Muscle tone decreases
• DIAZEPAM - It has useful antispastic
activity. Can be used in relieving muscle
spasm and muscle trauma.
• BACLofEN – It is a GABA –B Agonist. It
depress the mono synaptic and polysypnatic
reflexes in the spinal cord. It also relieves
• Uses: Musculo skeletal disorder, Sprain,
Myalgia, Low backache, Arthritis etc.
– Spastic Neurological disorder - Polio,
hemiplegia, quadriplegia are treated wil
diazepam or baclofen.
• Tetanus – Diazepam given IV.
• ECT – Diazepam given along with
peripherally acting SMR.
• Orthopaedic – Used for fracture
DIRECTLY ACTING MUSCLE
It directly affects the skeletal muscles
It inhibits the muscle contraction by
preventing Ca release
• Adverse Effects – It includes
– Drowsiness, Dizziness, Fatigue, Muscle
weakness, rarely hepato toxicity.
Uses: In spastic disorders like hemiplegia and
paraplegia, Spinal injury, Multiple Sclerosis
and cerebral palsy.
Monitor respiration while on SMR.
Do not withdraw the drugs suddenly
Patient should avoid driving while taking drugs.