(1989; 60 pages) [French]
Group: depolarizing muscle relaxant
Injection: 50 mg (chloride)/ml in 2-ml ampoule
Powder for injection (chloride or bromide)
Suxamethonium is a short-acting muscle relaxant which exerts a depolarizing effect at the neuromuscular junction. It is metabolized rapidly, mainly by pseudo-cholinesterase, and excreted in the urine. Given intravenously it acts within 30 seconds and flaccid paralysis, preceded by fasciculation, lasts up to 5 minutes. This effect is not reversible pharmacologically.
To produce brief muscular paralysis during:
• endotracheal intubation
• orthopaedic manipulations
• electroconvulsive therapy.
The muscular relaxation produced by suxamethonium is generally more profound than that of the longer-acting non-depolarizing muscle relaxants, but the latter are more suitable when an extended effect is required.
Dosage and administration
Muscle relaxants should only be administered after induction of anaesthesia and when a secure airway has been established.
Adults: initially 1 mg/kg i.v. followed, when necessary, by supplements of 0.3 mg/kg. Repeat doses may cause bradycardia, which can be prevented by atropine 0.5-1 mg i.v.
Children: 1-2 mg/kg i.v. supplemented, when necessary, as above.
A more prolonged effect may be obtained in both adults and children by continuous intravenous infusion of 1-2 mg/minute. This sometimes results in a paradoxical and prolonged non-depolarizing muscle-relaxant action. Since this is only partially and temporarily reversible by neostigmine, ventilation must be assisted and subsequently monitored until spontaneous breathing is fully re-established.
• Suxamethonium is absolutely contraindicated if the anaesthetist is not confident of maintaining a clear airway.
• Known hypersensitivity to suxamethonium.
• Myasthenia gravis.
• A family history of malignant hyperthermia.
• Glaucoma and ocular surgery (since suxamethonium raises intraocular pressure).
• Genetically determined disorders of plasma pseudocholinesterase. (If effective enzyme levels are suspected to be low, a test dose of 5 -10 mg should be administered. Patients who develop respiratory depression requiring mechanically assisted ventilation should not receive suxamethonium again.)
• Hyperkalaemia resulting from severe burns, crush injuries or denervation, which may persist for up to 9 months after injury to the spinal cord (suxamethonium can further raise serum potassium concentrations and cause cardiac arrest).
Suxamethonium should be used, whenever possible, by an experienced specialist anaesthetist. Facilities for endotracheal intubation and mechanically assisted ventilation should be immediately to hand and ready for use.
Restoration of muscle tone should always be allowed to occur before a long-acting muscle relaxant (such as gallamine) is administered.
Use in pregnancy
Suxamethonium should be used in preterm pregnancy only when the need out weighs any possible risk to the fetus. It can be administered by intravenous infusion in obstetric practice for caesarean section since, unlike gallamine, it does not readily cross the placental barrier.
Skin rashes and anaphylactoid reactions, including bronchospasm and hypotension, have been reported.
Transient postoperative muscular pain is common, especially in ambulant outpatients.
Suxamethonium is claimed to have triggered the onset of malignant hyperthermic crisis in rare cases, in particular in patients receiving either ether or halothane. Cyanosis and cardiac dysrhythmias are succeeded by facial spasms, generalized rigidity, tachycardia, rapid breathing and profound hyperpyrexia. Anaesthesia should be discontinued as rapidly as possible. Treatment is directed to supportive measures including the administration of 100 % oxygen, the intravenous venous infusion of large volumes of cooled fluids, control of cardiac dysrhythmias and maintaining urinary output, if necessary with diuretics. Dantrolene can reduce spasticity by a direct action on skeletal muscle and, if available, should be administered intravenously as soon as possible if malignant hyperthermia is suspected (1 mg/kg initially repeated as necessary to a total of 10 mg/kg).
The effect of suxamethonium may be appreciably prolonged by cholinesterase inhibitors including ecothiopate eye drops and certain other drugs used in the treatment of glaucoma. Exposure to certain organophosphate insecticides may also prolong the effect of suxamethonium.
Cardiac dysrhythmias have been precipitated by suxamethonium in patients receiving cardiac glycosides.
Ventilation must be assisted for as long as muscular paralysis prevents the re-establishment of spontaneous respiration.
Suxamethonium injection is usually stable for 12 months when stored at 2-8°C and the powder is stable for at least 5 years when stored below 37°C and protected from light and moisture.