Photodegradation kinetics of lodenafil carbonate, structure elucidation of two major degradation products using UPLC-MS/MS and in vitro cytotoxicity Cristiane Franco Codevilla, * a Alini Dall Cortivo Lange, a Juliana Maria de Mello Andrade, a J´ eferson Segalin, b Pedro Eduardo Fr¨ oehlich a and Ana Maria Bergold a The photostability of lodenafil carbonate was studied and some degradation products were observed. A stability-indicating liquid chromatography method for the determination of lodenafil carbonate was used to determine the kinetics of photodegradation. The identification of two major photodegradation products was performed by an isocratic ultra performance liquid chromatography-tandem mass spectrometry method (UPLC-MS/MS). UPLC-MS/MS was carried out on a Watersâ Acquity Ultra Performance LC system coupled to a Micromassâ Quadrupole Time of Flight tandem mass spectrometer equipped with an electrospray ionization interface in positive ion mode. The column applied was Acquity UPLCâ BEH C18; the mobile phase consisted of a mixture of methanol–formic acid 0.1% pH 4.0 (55 : 45, v/v) at a flow-rate of 0.4 mL min 1 and UV detection at 290 nm. The photodegradation of lodenafil carbonate followed first-order reaction kinetics and the kinetic parameters of degradation rate constant and t 90% were calculated. Under photodegradation conditions, ion products were detected at m/z 393 (DP-1) and at m/z 377 (DP-2). The product DP-1 is 4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7- dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl)-benzenesulfonic acid and DP-2 probably is 4-ethoxy-3-(1- methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl) benzenesulfinic acid. The degraded samples of lodenafil carbonate were also evaluated in order to determine the in vitro cytotoxicity against mononuclear cells. Introduction Chemical and physical degradation of drugs may change their pharmacological effects, resulting in altered therapeutic efficacy as well as toxicological consequences. Quality should be main- tained under the different conditions encountered by pharma- ceutical products, during production, storage in warehouses, transportation, and storage in hospital and community phar- macies, as well as in the home. 1,2 Stress testing, also called forced degradation studies, is dened as the stability testing of drug substances and drug products under conditions exceeding those used for accelerated testing. It provides information about degradation mechanisms and identies potential degradation products and can be used to develop manufacturing processes or to select suitable packaging. 3–5 Since there has been a noticeable increase in the number of drugs, which have been revealed to be light sensitive, drug photostability is an emerging topic in the pharmaceutical research eld. 2,6 This current study focuses on lodenal carbonate, bis-(2- {4-[4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl) benzenesulfonyl] piperazin-1-yl}-ethyl) carbonate (Fig. 1), which is a dimer that acts as a prodrug delivering lodenal in vivo. Lodenal carbonate is a phospho- diesterase type 5 inhibitor developed in Brazil, used to treat male erectile dysfunction. 7–9 The literature presents the determination of lodenal carbonate in biological uids by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) 8 and in pharmaceutical formulations by spectrophotometric methods 10 Fig. 1 Chemical structure of lodenafil carbonate. a Programa de P´ os-Graduaç~ ao em Ciˆ encias Farmacˆ euticas, Faculdade de Farm´ acia, Universidade Federal do Rio Grande do Sul, 90610-000 Porto Alegre, RS, Brazil. E-mail: cristianefc@hotmail.com; Fax: +55 51 33085351; Tel: +55 51 33085351 b Instituto Nacional de Metrologia, Qualidade e Tecnologia – Inmetro, Brazil Cite this: Anal. Methods, 2013, 5, 6511 Received 29th July 2013 Accepted 9th September 2013 DOI: 10.1039/c3ay41273c www.rsc.org/methods This journal is ª The Royal Society of Chemistry 2013 Anal. Methods, 2013, 5, 6511–6516 | 6511 Analytical Methods PAPER Published on 10 September 2013. Downloaded by Universidade Federal do Rio Grande do Sul on 11/12/2013 19:14:55. View Article Online View Journal | View Issue