Formulation and stabilization of norfloxacin in liposomal preparations Iqbal Ahmad a , Adeel Arsalan a,b, ⁎, Syed Abid Ali b , Raheela Bano a , Iqra Munir b , Arif Sabah a a Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi 74600, Pakistan b HEJ Research Institute of Chemistry, International Center for Chemical and Biological Sciences (ICCBS), University of Karachi, Karachi 75270, Pakistan abstract article info Article history: Received 10 March 2016 Received in revised form 22 April 2016 Accepted 14 May 2016 Available online xxxx A number of liposomal preparations of norfloxacin (NF) containing variable concentrations of phosphatidylcho- line (PC) (10.8–16.2 mM) have been formulated and an entrapment of NF to the extent of 41.7–56.2% was achieved. The values of apparent first-order rate constants (k obs ) for the photodegradation of NF in liposomes (pH 7.4) lie in the range of 1.05–2.40 × 10 -3 min -1 compared to a value of 8.13 × 10 -3 min -1 for the photodegradation of NF in aqueous solution (pH 7.4). The values of k obs are a linear function of PC concentration indicating an interaction of PC and NF during the reaction. The second-order rate constant for the photochemical interaction of PC and NF has been determined as 8.92 × 10 -2 M -1 min -1 . Fluorescence measurements on NF in liposomes indicate a decrease in fluorescence with an increase in PC concentration as a result of formation of NF - species which exhibits poor fluorescence. Dynamic light scattering has shown an increase in the size of NF encap- sulated liposomes with an increase in PC concentration. The stabilization of NF in liposomes is achieved by the formation of a charge-transfer complex between NF and PC. © 2016 Elsevier B.V. All rights reserved. Keywords: Liposomal preparation Norfloxacin Kinetics Photodegradation Stabilization Charge-transfer complex 1. Introduction Liposomal drug delivery systems (LDDSs) are among the most effec- tive vehicles for the entrapment and delivery of drugs to specific sites. These systems have the advantage to stabilize the drug by entrapment externally as well as in the biological system internally. Remarkable progress has been made in the development of LDDSs for pharmaceuti- cal, medical, cosmetic and neutraceutical applications (Gomez-Hens and Fernandez-Romero, 2006; Akbarzadeh et al., 2013; Allen and Cullis, 2013; Cagdas et al., 2014; Garg and Goyal, 2014; Stiufiuc et al., 2015; Daraee et al., 2014). Liposomal preparations are nontoxic, bio- compatible and biodegradable. They enhance the stability of the drugs against pH, light and enzymatic degradation. Liposomal drugs possess increased efficacy and therapeutic index with reduced drug toxicity (Gomez-Hens and Fernandez-Romero, 2006; Chang and Yeh, 2012; Slingerland et al., 2012; Allen and Cullis, 2013). Several drugs have been photostabilized in the form of liposomal preparations such as ribo- flavin (Loukas et al., 1995; Bhowmik and Sil, 2004; Ahmad et al., 2015a), doxorubicin (Bandak et al., 1999), amlodipine (Ragno et al., 2003), tretinoin (Ioele et al., 2005), barnidipine (Ioele et al., 2014), 4- nerolidylcatechol (Gaetil et al., 2015), and nimodipine and felodipine (Brito et al., 2012). In view of the photosensitivity and wide spread use of fluoroquinolones as antibacterial agents for a variety of ailments attempts have been made to stabilize them by entrapment in liposomes (Vazquez et al., 2001; Budai et al., 2008; Isabel and Paula, 2013). This could further be improved by an increase in the entrapment efficacy of fluoroquinolones (Ellbogen et al., 2003; Hosny, 2010). The interaction of fluoroquinolones with phospholipid bilayers in liposomes has also been studied by several workers (Bedard and Bryan, 1989; Maurer et al., 1998; Vazquez et al., 1998, 2001; Grancelli et al., 2002; Bensikaddour et al., 2008). However, no mechanism of these interac- tions has been reported so far. Norfloxacin (NF), a fluoroquinolone with a piperazinyl side chain (Fig. 1), is sensitive to light (USP-NF, 2014) and undergoes degradation in the aqueous solution (Nangia et al., 1991; Cordoba–Diaz et al., 1998; Zhang et al., 2012; Chen and Chu, 2012; Babic et al., 2013; Ahmad et al., 2015b) and in the solid state (Vazquez et al., 2001; Budai et al., 2008). The kinetics and pathways of photodegradation reactions of NF in aque- ous and organic solvents have been reported (Albini and Monti, 2003; Ahmad et al., 2015b). In the present work the photodegradation of NF in different liposomal preparations has been studied using HPLC and spectrofluorimetry. The physical characteristics of liposomal prepara- tions have been studied by DLS. The effect of compositional variations of phospholipids in liposomes on the photodegradation and stabiliza- tion of NF has also been evaluated. 2. Materials and methods Norfloxacin (≥ 98%, NF) and cholesterol (99%, CH) were purchased from Sigma-Aldrich (USA). Phosphatidylcholine (PC) was obtained from Avanti Polar Lipids, USA. All solvents and reagents were of HPLC grade form Merck (USA). Deionized water (16.5 MΩ resistance) from milli-Qpore system (Bedford, USA) was used for HPLC work. The sol- vents and the solutions were filtered using a Millipore filtration unit European Journal of Pharmaceutical Sciences xxx (2016) xxx–xxx ⁎ Corresponding author at: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi 74600, Pakistan. E-mail address: adeelarsalan@hotmail.com (A. Arsalan). PHASCI-03581; No of Pages 8 http://dx.doi.org/10.1016/j.ejps.2016.05.017 0928-0987/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect European Journal of Pharmaceutical Sciences journal homepage: www.elsevier.com/locate/ejps Please cite this article as: Ahmad, I., et al., Formulation and stabilization of norfloxacin in liposomal preparations, European Journal of Pharmaceu- tical Sciences (2016), http://dx.doi.org/10.1016/j.ejps.2016.05.017