Skeletal Muscle Relaxants

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Chapter: Medicinal Chemistry : Skeletal Muscle Relaxants

Skeletal muscle relaxants are drugs that are able to reduce unwanted spasm or spasticity without interfering with consciousness and normal voluntary movements.


Skeletal Muscle Relaxants

INTRODUCTION

Skeletal muscle relaxants are drugs that are able to reduce unwanted spasm or spasticity without interfering with consciousness and normal voluntary movements. These drugs may find an important application in various neurological or muscular skeletal disorders.

Drugs that cause depression of the motor functions leading to a relaxation of voluntary muscles are known as muscle relaxants. Drugs that act on the skeletal muscles fall into two major therapeutic groups, those used during surgical procedures and in intensive care units to cause paralysis (i.e. neuromuscular blockers) and those used to reduce spasticity in a variety of neurological conditions (i.e. spasmolytic). Neuromuscular blockers inhibit the transmission at the neuromuscular end plate and blocks central nervous system control. These components are used primarily as adjuvant to general anaesthesia.

In the 16th century, European explorers found that the natives of Amazon Basin of South America were using an arrow poison (Curare) that produced death by skeletal muscle paralysis. The active compound from curare, d-tubocurarine, and its synthetic derivatives had an enormous influence on the practice of anaesthesia and surgery.

In practice, the blockade of end plate function is accomplished by two basic mechanisms. Pharmacological blockade of physiological agonist acetylcholine is characteristic of the neuromuscular blocking drugs. These drugs prevent access of transmitters to the receptor and prevent depolarization. The prototype of this nondepolarizing subgroup is d-tubocurarine. Blocking of transmission can also be produced by an excess of depolarizing agonist, namely, acetylcholine and the depolarizing blocking drug, succinylcholine.

Skeletal muscle contractions occur when there is a release of acetylcholine from presynaptic vesicles, and acts on the postjunctional acetylcholinergic receptors in the motor end plate. An autoimmune disease, myasthenia gravis, associated with skeletal muscle relaxation is produced due to the loss of acetylcholinergic receptors in the neuromuscular junction. In normal physiological conditions, relaxation can be produced by the skeletal muscle relaxant, which binds to antagonize the action of acetylcholine on neuromuscular junction’s acetylcholine receptors.


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