Major degradation product identified in several pharmaceutical formulations against the common cold.

Different pharmaceutical preparations against the common cold containing acetaminophen, phenylephrine hydrochloride, and chlorpheniramine have been studied. An unidentified degradation product has been discovered in these preparations after short- and long-term stability studies, with increasing concentration at increasing storage temperatures and times. LC/MS was employed to identify and obtain molecular weights of the degradation products using an electrospray ionization interface. To obtain detailed structural information on the major degradation product, its isolation by SPE followed by HPLC was required. Final isolation was accomplished by using a new pentafluorophenyl stationary phase. Once the major degradation product was isolated, MS/MS, 1H NMR, 13C NMR, COSY, HMBC, and HSQC techniques permitted the complete characterization of this new compound formed under the usual stability conditions at climatic chambers. Its origin was also established as a result of the interaction between two of the components in the formulation. It is important to remark that this compound has not been described in the literature up to now and that, moreover, it has been identified in several commercial preparations containing phenylephrine hydrochloride and chlorpheniramine maleate.