Succinylcholine is composed of two molecules of acetylcholine. It binds to and stimulates cholinergic receptors at neuromuscular junction (1 mg/kg causes suppression of response to neuromuscular stimulation within 60 seconds).
Butyrylcholinesterase, which is synthesized in liver and is not present at the NMJ, rapidly hydrolizes succinylcholine to succinylmonocholine and choline. Note that only 10% of administered succinylcholine reaches neuromuscular junction.
Butyrylcholinesterase (Pseudocholinesterase) Deficiency:
- Levels can be affected by liver disease, advanced age, malnutrition, pregnancy, burns, OCP, etc.
- Large decreases in butyrylcholinesterase causes only moderate increase in duration of action of succinylcholine
Dibucaine inhibits normal enzyme to far greater extent that variant. Thus, if the dibucaine number is low (i.e. the native enzyme is not inhibited by dibucaine), one should suspect an abnormal variant of butyrylcholinesterase.