Isolation of a 2 : 1 hydrochlorothiazide-formaldehyde adduct impurity in hydrochlorothiazide drug substance by preparative chromatography and characterization by electrospray ionization LC-MS

Hydrochlorothiazide drug substance (19 lots) from five different manufactur ers and four different countries of origin (USA, Italy. Hungary. and Croati a) were analyzed for the presence of impurities using a gradient elution ch romatographic system, with acetonitrile-water as the mobile phase. Two know n impurities of hydrochlorothiazide, 4-amino-6-chloro-1,3-benzenedisulfonam ide and chlorothiazide, were separated. as well as a late-eluting, unknown, recurring impurity. The unknown impurity was isolated by preparative liqui d chromatography followed by preparative thin-layer chromatography, It was characterized by electrospray ionization LC-MS as a 2:1 hydrochlorothiazide -formaldehyde adduct of the parent drug substance. The adduct is believed t o form through the double condensation reaction of hydrochlorothiazide with excess formaldehyde during the parent compound's synthesis. The concentrat ion of this impurity ranged from 0.02 to 1.1%, (area%), and was above the 0 .1% USP Other Impurities threshold in 16 of the 19 lots examined. (C) 2001 Published by Elsevier Science B.V. All rights reserved.