title: Reaction between drug substances and pharmaceutical excipients: formation of citric acid esters and amides of carvedilol in the solid state.
abstract: The reactivity of citric acid towards drug substances in the solid state was examined using the beta-blocker carvedilol as a model compound. The reaction mixtures were analysed by LC-MS, the reaction products were isolated by preparative HPLC, and the structures were elucidated by microprobe NMR spectroscopy. Heating a mixture of solid carvedilol and solid citric acid monohydrate for 96 h at 50 degrees C resulted in the formation of about 3% of a symmetrical ester as well as of a number of other reaction products in smaller amounts. Formation of the symmetrical ester was also observed at room temperature. At 70 degrees C, the amounts of three isomeric esters formed reached 6-8%. The minor reaction products were citric acid amides, O-acetylcarvedilol, and esters of itaconic acid.
authors.affiliation: Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark. jl@farma.ku.dk
authors.forename: Jesper
authors.initials: J
authors.lastname: Larsen
authors.forename: Claus
authors.initials: C
authors.lastname: Cornett
authors.forename: Jerzy W
authors.initials: JW
authors.lastname: Jaroszewski
authors.forename: Steen H
authors.initials: SH
authors.lastname: Hansen
mesh_terms: D000577:Amides / Q000737:chemistry*; D002227:Carbazoles / Q000737:chemistry*; D000077261:Carvedilol; D055598:Chemical Phenomena; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002853:Chromatography, Liquid / Q000379:methods; D019343:Citric Acid / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D005079:Excipients / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D011412:Propanolamines / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
chemical_list: D000577:Amides; D002227:Carbazoles; D004952:Esters; D005079:Excipients; D011412:Propanolamines; D000077261:Carvedilol; D019343:Citric Acid