Neuromuscular blocking agents

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Chapter: Medicinal Chemistry : Skeletal Muscle Relaxants

Skeletal Muscle Relaxants : Neuromuscular blocking agents - Synthesis and Drug Profile - i. Gallamine triethiodide (Flaxedil) ii. Succinyl Choline Chloride b. Depolarizing neuromuscular blockers a. Nondepolarizing blockers - Structure, Properties, uses, Synthesis, Assay, Storage, Dosage forms, Dose | Synthesis and Drug Profile


Neuromuscular blocking agents

a. Nondepolarizing blockers

Mode of action: Nondepolarizing blockers have affinity for the cholinergic receptors at the muscle end plate. The receptor is a protein with five subunits arranged similar to a rosette, surrounding the sodium channel. The two subunits carry two acetylcholine binding sites; they have negatively charged groups, which combine with the cationic head of acetylcholine leads to the opening of sodium channel. Most of the nondepolarizing blockers have two or more quaternary nitrogen atoms, which provide the necessary attraction to the same site for binding, so acetylcholine released from the nerve ending cannot be able to bind to generate action potential and produces muscle relaxant property.

i. Gallamine triethiodide (Flaxedil)


Propperties and uses: It is a white or almost white powder hygroscopic in nature. Insoluble in methylene chloride, soluble in water, and slightly soluble in alcohol. It is a nondepolarizing neuromuscular blocker used as adjuvant to anaesthesia, so as to achieve depot muscular relaxation.

Assay: Dissolve the sample in a mixture of anhydrous formic acid and acetic anhydride. Titrate with 0.1 M perchloric acid and determine the end point potentiometrically.

Storage: It should be stored in well-closed airtight containers and protected from light.

Dose: For the treatment of limb muscle paralysis, initial dose by I.V. or I.M. 1 mg/kg of body weight; for abdominal surgery, 1.5 mg/kg of body weight; maintenance dose is 500 μg to 1mg every 30 to 60 min, intervals, if required. The dose must be reduced when used along with anaesthetics like ether, cyclopropane, etc.

Dosage forms: Gallamine triethiodide injection I.P., Gallamine injection B.P.

b. Depolarizing neuromuscular blockers

Mode of action: These drugs depolarize the muscle end plate potential by opening of Na+ channels as acetylcholine initially produce twitching and fasciculation. They do not dissociate rapidly from the receptors, and produce prolonged partial depolarization of muscles and plates leading to inactivation of sodium channels due to the dropping of membrane potential.

ii. Succinyl Choline Chloride


Uses: It is used to relax the skeletal muscle for orthopaedic manipulation of endotrachial-intubation.

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