Determination of succinylcholine in plasma by high-pressure liquid chromatography with electrochemical detection

The plasma concentration of the neuromuscular blocking drug, succinylcholine, is difficult to measure. We have measured concentrations of the breakdown product of succinylcholine, choline, to assess whether choline concentration gives an accurate measure of succinylcholine concentration. Choline concentration was measured by HPLC and electrochemical detection in two blood or plasma samples, one in which succinylcholine hydrolysis was inhibited by 10(-5) M physostigmine and another in which succinylcholine was completely hydrolysed in 20 min by 200 mU butyrylcholinesterase at 37 degrees C. The difference in choline content between the two samples gives the succinylcholine concentration. Ninety-five per cent recovery of choline was achieved. Choline standard curves were linear from 156 pmol ml-1 to 200 nmol ml-1. Within-day and between-day mean coefficients of variation for succinylcholine hydrolysis were small (mean (SD) 3.7% (1.2%) and 3.8% (1.6%), respectively). We conclude that this method of measuring succinylcholine concentration in blood is accurate, repeatable and relatively easy.