Watson B L, Cormier R A, Harbeck R J
Department of Medicine, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206, USA.
Respir Med. 1998 Mar;92(3):588-92. doi: 10.1016/s0954-6111(98)90314-6.
Methacholine chloride bronchoprovocation challenges are performed for the diagnosis and investigation of hyperreactive airways. Over the last 20 yrs various formulations and pH values for the preparation of solutions of methacholine have been described. To determine the stability of methacholine chloride solutions prepared in a variety of buffers with differing pH values and under varying storage temperatures, we measured methacholine concentrations at intervals from 1 to 5 weeks. It was found that methacholine chloride solutions rapidly decompose if the pH is greater than 6 and that decomposition is more rapid as the pH is raised; solutions at pH 9, i.e. bicarbonate buffer, and stored at 27 degrees C have degradation up to 36% after only one week. Solutions of the same pH but prepared in different buffers can have both varied rates of deterioration and different absolute amounts of methacholine hydrolysed, e.g. solutions prepared in pH 9 borate buffer and stored at 27 degrees C have up to 60% degradation after 1 week. Solutions prepared in saline are stable probably because methacholine solutions are weakly acidic. The results emphasise the importance of preparing methacholine chloride in the proper buffers for use in the accurate assessment of airway responsiveness.
进行氯化乙酰甲胆碱支气管激发试验以诊断和研究气道高反应性。在过去20年中，已经描述了用于制备乙酰甲胆碱溶液的各种配方和pH值。为了确定在不同pH值的各种缓冲液中以及在不同储存温度下制备的氯化乙酰甲胆碱溶液的稳定性，我们在1至5周的间隔内测量了乙酰甲胆碱浓度。发现如果pH值大于6，氯化乙酰甲胆碱溶液会迅速分解，并且随着pH值升高分解更快；pH为9的溶液，即碳酸氢盐缓冲液，在27℃储存时，仅一周后降解率就高达36%。相同pH值但在不同缓冲液中制备的溶液可能具有不同的降解速率和不同的乙酰甲胆碱水解绝对量，例如在pH为9的硼酸盐缓冲液中制备并在27℃储存的溶液，1周后降解率高达60%。在盐水中制备的溶液是稳定的，可能是因为乙酰甲胆碱溶液呈弱酸性。结果强调了在适当的缓冲液中制备氯化乙酰甲胆碱以用于准确评估气道反应性的重要性。
