SKELETAL MUSCLE RELAXANTS

By: Mrs. Kalaivani Sathish, M. PharmAssistant Professor,

PIMS - PANIPAT

INTRODUCTION

• 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.

CLASSIFICATION

PERIPHERALLY ACTING SKELETAL MUSCLE RELAXANTS

• NEUROMUSCULAR BLOCKERS (NMB)• Competitive BlockersD – 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.

MECHANISM OF ACTION• Non depolarizing blockers binds to

nicotinic receptors

• Blocks the action of Ach

PHARMACOLOGICAL ACTION OF TUBOCURARINE

• 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 causes hypotension.

• Histamine Release – Bronchospasm, ed tracheo bronchial and gastric secretions occurs due to the release of histamine. This in turn leads to hypotension.

PHARMACOKINETICS &

ADVERSE EFFECTS• 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 bronchospasm.

• 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 of histamine.

• Synthetic competitive blocker :• Pancuronium, vecuronium, atracuronium, have

intermediate onset ( 2 – 4 minutes ) while rapacuronium and rocuronium have fast onset of action ( 1 – 2 minutes ) .

Depolarising Blocker

• 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 .

Depolarising Blocker • Mechanism of action :• succinyl choline • • Nicotinic receptor • • Membrane depolarization • • Peristant depolarisation • • Flaccid paralysis

Depolarising Blocker • 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 muscle paralysis.

• CVS:• Initially hypotension and bradycardia may result from

stimulation of vagal ganglia .this is followed by hypertension and tachycardia due to stimulation of sympathetic ganglia.

Depolarising Blocker • 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.

•

Depolarising Blocker • 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 sites.• Cardiac arrhythmias :• SCh can cause cardiac arrhythmias.

•

Depolarising Blocker • 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 drug.6. Ventilators: SMR are used to enhance artificial

respiration.

CENTRALLY ACTING MUSCLE RELAXANTSThese drugs acts on higher centre and cause muscle relaxation

without loss of consciousness. They also have sedative properties.

•

CENTRALLY ACTING MUSCLE RELAXANTS

mechanism of action CAMR 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 painful spasm.

• 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 reduction.

DIRECTLY ACTING MUSCLE RELAXANTS

It directly affects the skeletal muscles contractile mechanism.

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.

Nursing Implications:Monitor respiration while on SMR.Do not withdraw the drugs suddenlyPatient should avoid driving while taking drugs.