It is indicated as an adjunct to general anesthesia,to facilitate tracheal intubation,and to provide skeletal muscle relaxation during surgery or mechanical ventilation. in various orthopedic manipulations and endoscopic examinations. to reduce the intensity of muscular contractions associated with pharmacologically or electrically-induced convulsions.
Depolarizing muscle relaxants
Suxamethonium is a muscle relaxant. It acts as a depolarizing neuromuscular blocker by imitating the action of acetylcholine at the neuromuscular junction. Suxamethonium acts on muscle type nicotinic receptors. Binding of Suxamethonium to the nicotinic acetylcholine receptor results in opening of the receptor's nicotinic sodium channel; sodium moves into the cell, a disorganized depolarization of the motor-end plate occurs and calcium is released from the sarcoplasmic reticulum. This results in fasciculation. In the normal muscle, following depolarization, acetylcholine is rapidly hydrolyzed by acetylcholinesterase and the muscle cell is able to 'reset' ready for the next signal. But Suxamethonium is degraded not by acetylcholinesterase, rather by butyrylcholinesterase, a plasma cholinesterase. This hydrolysis by butyrylcholinesterase is much slower than that of acetylcholine by acetylcholinesterase. Thus Suxamethonium has a longer duration of effect than acetylcholine and it does not allow the muscle cell to 'reset' and keeps the 'new' resting membrane potential below threshold. When acetylcholine binds to an already depolarized receptor it cannot cause further depolarization. Calcium is removed from the muscle cell cytosol independent of repolarization. As the calcium is taken up by the sarcoplasmic reticulum, the muscle relaxes. This explains muscle flaccidity rather than tetany following fasciculation.
The dosage of it should be individualized and should always be determined by the clinician after careful assessment of the patient. The dose is dependent on body weight,the degree of muscle relaxation required and the response of individual patients. By intravenous injection: It injection is given intravenously over 10 to 30 seconds. The average dose required to produce neuromuscular blockade and to facilitate tracheal intubations is 0.6 mg/kg (range 0.3-1.1 mg/kg). This dose produces muscle relaxation in about 60 seconds and has a duration of approximately 4 to 6 minutes. Larger doses produce more prolonged muscle relaxation. By intravenous infusion: The dose of It administered by infusion depends upon the duration of the surgical procedure and the need for muscle relaxation. The average rate for an adult ranges between 2.5 and 4.3 mg per minute; max 500 mg/hour. Solutions containing from 1 to 2 mg per mL Suxamethonium Chloride diluted in 5% dextrose solution have commonly been used for continuous infusion. Pediatrics: For emergency tracheal intubation or in instances where immediate securing of the airway is necessary,the IV dose of It is 2 mg/kg for infants and small children (under one year); for older children and adolescents (over one year) the dose is 1 mg/kg. Intramuscular Use: If necessary,It may be given intramuscularly to infants, older children,or adults when a suitable vein is inaccessible. A dose of up to 3 to 4 mg/kg may be given,but not more than 150 mg total dose should be administered by this route. The onset of effect of Suxamethonium Chloride given intramuscularly is usually observed in about 2 to 3 minutes.
Certain drugs or chemicals are known to reduce normal plasma cholinesterase activity and may therefore prolong the neuromuscular blocking effects of Suxamethonium. These include: trimetaphan; specific anticholinesterase agents: neostigmine, pyridostigmine, physostigmine; cytotoxic compounds: cyclophosphamide, mechlorethamine, triethylene-melamine; psychiatric drugs: promazine and chlorpromazine, anesthetic agents and drugs: ketamine, morphine and morphine antagonists, pethidine, pancuronium.
Suxamethonium Chloride is contraindicated in persons with personal or familial history of malignant hyperthermia,skeletal muscle myopathies,and known hypersensitivity to the drug. It is also contraindicated in patients after the acute phase of injury following major burns,multiple trauma,extensive denervation of skeletal muscle,or upper motor neuron injury,because Suxamethonium Chloride administered to such individuals may result in severe hyperkalemia which may result in cardiac arrest . The risk of hyperkalemia in these patients increases over time and usually peaks at 7 to 10 days after the injury. The risk is dependent on the extent and location of the injury. The precise time of onset and the duration of the risk period are not known.
Muscle pains are frequently experienced after administration of Suxamethonium Chloride. It also may cause prolonged apnea. Hypersensitivity reactions,including anaphylaxis,may occur in rare instances. The administration of Suxamethonium Chloride may be followed by bradycardia,often associated with cardiac arrhythmia. Sinus tachycardia and hypertension has occurred after the continuous infusion of Suxamethonium Chloride. Myoglobinuria has been reported either alone or associated with malignant hyperexia.
Pregnant patients may be expected to show increased sensitivity to Suxamethonium Chloride,because plasma cholinesterase levels are decreased by approximately 24% during pregnancy and for several days postpartum. Therefore,Suxamethonium Chloride should be given to a pregnant woman only if clearly needed. Under normal conditions the quantity of drug that enters fetal circulation after a single dose of 1 mg/kg to the mother should not endanger the fetus. It is not known whether Suxamethonium Chloride is excreted in human milk. Caution should be exercised following Suxamethonium Chloride administration to a nursing woman.
The most serious effects of overdosage are apnoea and prolonged muscle paralysis. It is essential to
maintain the airway and adequate ventilation until spontaneous respiration is fully restored.
The use of neostigmine to reverse a nondepolarising block is a clinical decision which depends on
the subject, the experience, and the judgment of the clinician. If neostigmine is used, its
administration should be accompanied by an appropriate dose of atropine.
Store in a refrigerator between 2°-8° C. Do not freeze.
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