Studies on Decomposition and Stabilization of Drugs in Solution. X. Chemical Kinetic Studies on Aqueous Solution of Succinylcholine Chloride. 2. Overall Velocity Constants for Succinylcholine Chloride Hydrolysis as a Function of pH.

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1) The degradative reaction of succinylcholine chloride was investigated over the pH range of 0.9 to 8.5 by ion exchange chromatographic method from the standpoint of chemical kinetics. The decomposition was recognized as a first-order reaction at any given pH value with respect to succinylcholine chloride. From the data obtained at the lower pH regions, there action constants (L.·mol.-1·hr.-1) catalyzed by hydrogen ion were determined as follows:
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2) From the data obtained at higher pH regions, the presence of catalysis of general base besides hydroxyl ion was shown. It was recognized that the velocity constant was affected by a buffer concentration even in the same pH and the same ionic strength.
3) From the observed rate constants against varying acetate ion concentrations in the acetate buffers (μ=0.2) for two different pH values (4.69, 3.98) at 60°, the secondorder rate constant, k_CH3COO^-, was determined as 5.01×10^-2 (L.·mol.^-1·hr.^-1).
4) The catalytic constant (L.·mol.^-1·hr.^-1) of hydroxyl ion, k_OH^-, for succinylcholine chloride was obtained, maintaining at the initial pH value without buffering agent. The reaction constants catalyzed by hydroxyl ion were determined as follows:
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5) The rate constant (hr.^-1) in an acetate buffer (μ=0.2) at an optional concentration was expressed as follows:
k=6.47×10^-1 (H⁺) +5.01×10^-6 (H₂O) +2.04×10⁵ (OH^-) +5.01×10^-2 (CH₃COO^-)
It was concluded that the use of buffering agent is not always recommended for the storage of succinylcholine chloride solution, because it accelerates hydrolysis of succinylcholine chloride.