Biological Functions
Succinylcholine is given systemically because the molecule
is charged and does not easily cross membranes. It is
rapidly hydrolyzed by plasma cholinesterase to succinylmonocholine,
which is pharmacologically inactive. Because
plasma cholinesterase is synthesized in the liver,
neuromuscular block may be prolonged in patients with
liver disease. About 10% of succinylcholine is excreted
unchanged in the urine. The response to succinylcholine
may also be prolonged in individuals with a genetic defect
leading to atypical plasma cholinesterase (homozygous
incidence of about 1 in 2,500). In this case, the enzyme has
a decreased affinity for substrates such as succinylcholine
that can be measured by the dibucaine test.
