Dreijer-van der Glas S M, Bult A
Pharm Weekbl Sci. 1987 Feb 20;9(1):29-32. doi: 10.1007/BF01956489.
Eye drop formulations containing indometacin and benzalkonium salt often show an opalescence as a result of ion-pair formation. The insoluble ion pair was isolated and characterized by infrared and ultraviolet spectroscopy and thin layer chromatography. This ion pair is also responsible for the bad assay results of benzalkonium using the ion-pair extraction method with bromothymol blue as counterion. The distribution constant (KD = 1O4) of indometacin and the extraction constant (Kex = 3 X 1O4) of the ion pair indometacin-benzalkonium in a water-chloroform system at various pH values were determined. A discussion on the preservation of indometacin eye drop formulations with benzalkonium salt in view of this chemical incompatibility is presented.
含有吲哚美辛和苯扎氯铵盐的滴眼液制剂常因离子对形成而出现乳光现象。分离出不溶性离子对，并通过红外光谱、紫外光谱和薄层色谱对其进行表征。该离子对也是导致以溴百里酚蓝为反离子采用离子对萃取法测定苯扎氯铵时结果不佳的原因。测定了吲哚美辛在水 - 氯仿体系中不同pH值下的分配常数（KD = 10⁴）以及离子对吲哚美辛 - 苯扎氯铵的萃取常数（Kex = 3×10⁴）。鉴于这种化学不相容性，对含苯扎氯铵盐的吲哚美辛滴眼液制剂的保存进行了讨论。
