Abstract
The aim of the research effort entertained herein was to develop, evaluate and fully characterize a multiparticulate floating gastroretentive system for the modified release of zidovudine (AZT), an antiretroviral drug. AZT was used as a water-soluble model drug at therapeutic doses. The floating gastroretentive system was obtained via polymer coating of calcium silicate-adsorbed AZT. The proposed system was evaluated in vitro for particle micromorphology, lag time for floating and duration of floating, drug loading capacity, drug release profile, and drug release kinetics. The physicochemical properties of AZT were evaluated by scanning electron microscopy (SEM) analyses, differential scanning calorimetry (DSC) analyses, X-ray diffraction (XRD) analyses, and infrared spectroscopy (FTIR) analyses. Results from SEM analysis of the AZT-containing floating gastroretentive granules allowed observation of an irregular surface and the apparent absence of pores. Floating of the AZT-containing gastroretentive granules was immediately achieved, that is lag time for floating was virtually zero and duration of floating was higher than 12 h. The drug loading capacity of the floating gastroretentive granules was ca. 81.09 ± 14.66%, and the release system thus obtained exhibited an extended drug release profile. Results from DSC and XRD analyses showed a modification in the AZT solid state, while the FTIR spectroscopy analyses revealed that the chemical structure of AZT remained unchanged upon adsorption to calcium silicate followed by polymeric coating. Hence, the coated granules produced presented gastroretentive, floating, and extended drug release properties. Key words: Zidovudine, cal-sil floating granules, gastroretentive floating system, extended drug release, zidovudine (AZT), polymer coating.
Highlights
The gastrointestinal tract (GIT) has a natural physiological and anatomical barrier that makes difficult the absorption of drugs after their oral administration
The physicochemical properties of AZT were evaluated by scanning electron microscopy (SEM) analyses, differential scanning calorimetry (DSC) analyses, X-ray diffraction (XRD) analyses, and infrared spectroscopy (FTIR) analyses
Results from DSC and XRD analyses showed a modification in the AZT solid state, while the Fourier transform infrared (FTIR) spectroscopy analyses revealed that the chemical structure of AZT remained unchanged upon adsorption to calcium silicate followed by polymeric coating
Summary
The gastrointestinal tract (GIT) has a natural physiological and anatomical barrier that makes difficult the absorption of drugs after their oral administration. Reason for the poor drug absorption in these anatomical segments lies in the relatively short transit time, which is mainly due to the gastric emptying rate (Narendra et al, 2006; Shah et al, 2009) In such cases, the control of drug residence time, aiming at increasing drug retention time in the stomach, is a valuable resource to improve bioavailability (Shah et al, 2009; Arora et al, 2005). Jain et al (2008) investigated the use of ranitidine hydrochloride as a model drug adsorbed onto calcium silicate doubly coated with hydroxypropylmethylcellulose and ethylcellulose dispersions, obtaining a system consisting of polymeric-coated granules that exhibited a gastroretentive release profile with a flotation duration timeframe of 8 h Both in vitro and in vivo assays demonstrated the potential of that system for attaining the sustained release of the drug when compared with their non-floating counterparts. The major goal of the research effort entertained was to optimize, prepare, and fully characterize physicochemically, a floating multiparticulate gastroretentive system for the extended release of AZT, consisting of calcium silicate, ethylcellulose, hydroxypropylmethylcellulose and Eudragit® L100
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