Adults: For Short Surgical Procedures: the average dose required to produce neuromuscular blockade and to facilitate tracheal intubation is 0.6 mg/kg ANECTINE (Succinylcholine Chloride Injection) given intravenously. The optimum dose will vary among individuals and may be from 0.3 to 1.1 mg/kg for adults. Following administration of doses in this range, neuromuscular blockade develops in about 1 minute; maximum blockade may persist for about 2 minutes, after which recovery takes place within 4 to 6 minutes. However, very large doses may result in more prolonged blockade. A 5- to 10-mg test dose may be used to determine the sensitivity of the patient and the individual recovery time (see PRECAUTIONS). For Long Surgical Procedures The dose of succinylcholine 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. Solutions containing from 1 to 2 mg per mL succinylcholine have commonly been used for continuous infusion. The more dilute solution (1 mg per mL) is probably preferable from the standpoint of ease of control of the rate of administration of the drug and, hence, of relaxation. This IV solution containing 1 mg per mL may be administered at a rate of 0.5 mg (0.5 mL) to 10 mg (10 mL) per minute to obtain the required amount of relaxation. Intermittent IV injections of succinylcholine may also be used to provide muscle relaxation for long procedures. An IV injection of 0.3 to 1.1 mg/kg may be given initially, followed, at appropriate intervals, by further injections of 0.04 to 0.07 mg/kg to maintain the degree of relaxation required. Pediatrics: for emergency tracheal intubation or in instances where immediate securing of the airway is necessary, the IV dose of succinylcholine is 2 mg/kg for infants and small children; for older children and adolescents the dose is 1 mg/kg. Rarely, IV bolus administration of succinylcholine in infants and children may result in malignant ventricular arrhythmias and cardiac arrest secondary to acute rhabdomyolysis with hyperkalemia. In such situations, an underlying myopathy should be suspected. Intravenous bolus administration of succinylcholine in infants or children may result in profound bradycardia or, rarely, asystole. As in adults, the incidence of bradycardia in children is higher Intramuscular Use: If necessary, succinylcholine 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 succinylcholine given intramuscularly is usually observed in about 2 to 3 minutes.

The rat diaphragm was used as an in vitro model for studies of contractures synergistically-induced by halothane and suxamethonium (succinylcholine). The effects of three agents reported to inhibit phospholipase A2 activity (quinacrine, spermine and indomethacin), tubocurarine and dantrolene were examined on these contractures. Contractures induced by 1% halothane (0.26 +/- 0.02 g) (mean +/- SEM) were increased (0.60 +/- 0.04 g) if suxamethonium 50 mmol litre-1 was also in the bathing medium. Suxamethonium-induced contractures (0.22 +/- 0.03 g) were also enhanced when halothane was present (0.51 +/- 0.03 g). Spermine, indomethacin and dantrolene antagonized both halothane- and suxamethonium-induced contractures. Quinacrine potentiated contractures induced by either halothane or suxamethonium. Contractures induced by suxamethonium were antagonized by tubocurarine; however, contractures induced by halothane were not antagonized by tubocurarine. These results suggest that free fatty acids may be involved in contractures induced synergistically by halothane and suxamethonium. Different mechanisms are involved in the induction of contractures by suxamethonium than by halothane.