Succinylcholine Elimination from the Body
Succinylcholine is rapidly eliminated from the body, with plasma levels falling below detectable limits within 2.5 minutes after IV administration, and clinical paralysis lasting approximately 4-6 minutes with standard dosing. 1
Pharmacokinetics and Metabolism
Succinylcholine is rapidly hydrolyzed by plasma cholinesterase (pseudocholinesterase) to succinylmonocholine, which possesses clinically insignificant muscle relaxant properties, and then more slowly metabolized to succinic acid and choline. 1
Plasma levels of succinylcholine fall below the detection limit of 2 μg/mL after just 2.5 minutes following an IV bolus dose of 1-2 mg/kg in anesthetized patients. 1
Only about 10% of the drug is excreted unchanged in the urine. 1
Clinical Duration of Action
The duration of neuromuscular blockade varies with dose:
With standard 1.0 mg/kg dosing, clinical paralysis lasts approximately 4-6 minutes after a single IV administration. 1
Time to 90% twitch recovery at the adductor pollicis is approximately 9.3 ± 1.2 minutes with 1.0 mg/kg dosing. 2
Reducing the dose to 0.6 mg/kg shortens recovery time to approximately 7.6 ± 1.6 minutes, while 0.4 mg/kg results in recovery at 6.6 ± 1.5 minutes. 2
Detection Windows for Metabolites
While succinylcholine itself is eliminated extremely rapidly, its metabolite succinylmonocholine (SMC) persists longer:
In blood, succinylcholine is typically detectable for only up to 10 minutes post-injection, while SMC remains detectable for at least 6 hours. 3
In urine, succinylcholine has a detection window of minimum 2 hours, while SMC can be detected for at least 6 hours in freshly secreted urine. 3
Considering SMC plasma kinetics, detection of the metabolite in blood and freshly secreted urine appears possible over a period of at least 8-24 hours. 3
Important Clinical Caveats
Patients with pseudocholinesterase deficiency are at high risk for prolonged duration of action and increased metabolic complication risk, requiring extended monitoring. 4
The American Academy of Pediatrics notes that succinylcholine's metabolic effects (including potential hyperkalemia) extend beyond its neuromuscular blocking duration, emphasizing the need for extended monitoring in high-risk patients. 4
Tachyphylaxis occurs with repeated administration, and the characteristic Phase I depolarizing block may transition to a Phase II block with prolonged paralysis depending on dose and duration of administration. 1