Development of chitosan-based nanoparticles for pulmonary delivery of itraconazole as dry powder formulation

Abstract

The aim of current study was to illustrate a strategy to encapsulate itraconazole into chitosan-based nanoparticles using a modified ionic gelation method and to fabricate them as inhalable microparticles using spray drying technique. Different ratios of chitosan:tripolyphosphate (TPP) were prepared at pH 1.2, using higher ratios of TPP with respect to chitosan. The highest encapsulation efficiency of itraconazole into chitosan nanoparticles was found to be about 55% at 1:3 ratio of chitosan:TPP. Increasing the amount of TPP 4 times higher than chitosan resulted in the production of large particles in micron scale. Below the ratio of 1:3, the particle sizes ranged from 190 to 240 nm. Nanoparticles were characterized for morphology by TEM images. Microparticles were prepared by co-spray drying of nanoparticles with 2.5, 10 and 20% of lactose and mannitol with or without 10% of leucine, with respect to nanoparticle weights. In vitro inhalation parameters including fine particle fraction (FPF) and emitted dose percentage (ED%) were measured by a twin stage impinger (TSI). The in vitro deposition data indicated that processing of nanoparticles with mannitol and leucine could improve the aerosolization properties of the drug significantly.

Introduction

Invasive pulmonary aspergillosis is a major infectious disease among immunosuppressed patients [1], [2]. Complications due to delay in clinical diagnosis, poor response to antifungal treatment, and the high mortality percent have prompted efforts to find alternative drug delivery strategies [2], [3]. Aerosolization of antifungal agents is a promising approach for prophylaxis against pulmonary fungal infections. Passive targeting, achievement of high drug concentration in the site of infection, patient convenience due to the non invasive nature of this route of administration and reduced systemic toxicities are considered as some advantages of the application of aerosolized antifungal drugs [1], [4].

Itraconazole (ITRA) is a highly hydrophobic and weakly basic broad-spectrum antifungal azole and its aqueous solubility was reported to be about 1 ng/ml at pH 7 and 4 μg/ml at pH 1, respectively. ITRA, a class II member of biopharmaceutical classification, has some limitation using oral route of administration due to its low solubility [5]. Different formulation approaches like emulsification [6], [7], solid dispersion [8] and the use of solubilizer excipients have been used widely to enhance solubility of ITRA. Cyclodextrins are known as cyclic oligosaccharides that are used generally as solubilizing excipients for formulation of low water soluble compounds [9]. 2-Hydroxypropyl-beta-cyclodextrin (HPβCD), a hydrophilic cyclodextrin derivative, has been used in some marketed pharmaceutical formulations such as oral and intravenous ITRA (Sporanox®), intravenous mitomycin (Mitozytrex®) and cisapride suppository (Propulsid®) [9]. The solubility of water insoluble drugs, such as ITRA, can be enhanced by encapsulating them in the hydrophobic inner region of HPβCD. Some strategies like ionization, salt formation, formation of metal complexes and addition of organic co-solvents have been used to enhance the complexation efficiency and therefore, lower the required amount of cyclodextrins [9], [10].

The use of HPβCD has been examined by Evrard et al. as a carrier for pulmonary delivery via nebulization. Their results indicated that HPβCD could improve aerosolization and deposition characteristics of drug while no toxic effect was observed upon application of the solutions in in vivo experiments [11]. Also Yang et al. studied in vitro and in vivo pulmonary delivery of ITRA–HPβCD solution by means of nebulization [12]. The effect of HPβCD on aerosolization of drugs in dry powder formulations was also examined [13].

Different nanotechnology systems have been used to enhance the solubility and alter the pharmacokinetic parameters of ITRA [4], [14]. Furthermore, nanoparticles have shown the ability to enhance drug penetration and to improve antimicrobial activity of drugs. Ionotropic gelation is one of the methods that can be used to achieve a polymeric nanoparticulate system. Several publications reported this procedure by the use of chitosan, as a natural cationic polymer, and tripolyphosphate (TPP), as an oppositely charged entity, to entrap different drugs into the polymeric nanoparticles [15], [16], [17]. Furthermore, chitosan has mucoadhesive properties and can prolong residence time and the release of drugs into the lung [18].

Use of nanoparticles alone for inhalation has encountered some obstacles including the high aggregation of nanoparticles and exhalation of them. To overcome these problems and to provide a solid state and stable formulation, preparation of micron-scale dry powders containing nanoparticles by means of particle engineering techniques such as spray drying [19], [20], [21], [22], [23] has been considered as a promising solution. Also to prepare nanoparticles as inhalable dry powders with suitable median aerodynamic diameter for optimized alveolar deposition and to avoid aggregation of the nanoparticles, the use of carriers such as lactose and mannitol seems to be necessary [19], [22].

The aim of this study was to illustrate a strategy to fabricate ITRA-loaded nanoparticles by using ionic gelation method. Generally, in this method nanoparticles are prepared by addition of TPP solution (pH 7–9) into an acidic solution (pH 4–6) of chitosan [24]. The ratio between chitosan and TPP is critical, and highly dependent on pH of the solution. Because of the negligible aqueous solubility of ITRA, the complex of ITRA–HPβCD was used all throughout the experiments. At first this complex was fabricated into the chitosan–TPP nanoparticles to maintain the high solubility of the drug due to the increased surface area exhibited by nanoparticles, compared to inhalable microparticles. In our study, we prepared chitosan/TPP nanoparticles at pH as low as 1.2 which was required to solubilize the drug and to make ITRA–HPβCD complex. This pH was not usually used in preparation of chitosan nanoparticles by ionic gelation method. Therefore, the ratio of TPP and chitosan needed to be changed carefully. Finally, the physical and aerosolization properties of microparticles prepared by spray drying of ITRA–HPβCD loaded nanoparticles with lactose, mannitol and/or leucine were compared. Co-spray drying of the nanoparticles with these excipients could help us to benefit both the aerosolization properties of the microparticles and the delivery advantages of ITRA loaded nanoparticles.