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kaichang

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The objective of the present study was to employ suitable adsorbent with free ﬂowing characteristicsfor improving the stability and physical properties of solid lipid nanoparticles (SLN) for oral administration. Stearic acid based nanoparticles of carvedilol phosphate were fabricated by solvent emulsiﬁcation evaporation technique in sodium taurocholate solution prepared in pH 7.2 buffers (I—KH2PO4/NaOH or II—NaH2PO4/Na2HPO4) with 1% polyvinyl alcohol. Nanoparticles were then adsorbed by passing the nanodispersion through a Neusilin US2 (adsorbent) column. Interestingly, scanning electron microscopy revealed round deformed and even collapsed nanoparticles in Buffer-I and discrete spherical to ellipsoidal nanoparticles in Buffer-II which indicates the inability of nanoemulsion to crystallize and form SLN in Buffer-I. The successful formation of SLN in Buffer-II was conﬁrmed by differential scanning calorime try and X-ray diffraction. The retention of SLN from the nanodispersion by adsorption on the adsorbent imparted good ﬂow property and resulted in a marked stability improvement of the formulation in terms of drug retention efﬁciency and release proﬁle as compared to the simple nanosuspension. In conclusion, the adsorbent technology would be instrumental in imparting additional features to the existing conventional colloidal system for pharmaceutical application which would ease the process of capsule ﬁlling at industrial scale, simplify the handling of formulations by patients and can signiﬁcantly improve the shelf life of the product for a longer period of time as compared to liquid formulations. improve stability. However, the coexistence of high concentration of stabilizing agents (surfactants) along with the lipid nanopartiSolid lipid based colloidal carriers of drugs have attracted considerable attention in the last two decades [1–4]. As they are derived from physiologically compatible lipids, solid lipid nanoparticles (SLN) represent a safe and effective alternative which include additional advantages and are devoid of the potential toxicities of conventional polymeric nanoparticles [5–7]. SLN for oral drug administration have speciﬁcally been employed for improving bioavailability by targeting the uptake of the drug by lymphatic system which prevents its hepatic ﬁrst pass metabolism [8–11]. Despite the perceived therapeutic advantages of SLN, the technology available so far for the fabrication of SLN is restricted to the development of nanodispersion which has not had been so encouraging. In an aqueous nanodispersion, the SLN have a tendency to undergo particle aggregation under accelerated storage conditions due to the gelation phenomenon (an irreversible conversion of low viscosity lipid based nanoparticles dispersion into a viscous gel) due to which the dispersion is usually lyophilized into a dry powder to cles (LNs) in the ﬁnal product is not desirable because of their toxic effects on the mucosal lining of the GIT. Moreover, the process of lyophilization is critical as rate of freezing governs the structure and properties of the lipid crystals which ﬁnally determines its drug retention capacity during storage. Alternatively, ﬁltration of the nanoparticles as a whole is a costly and exhaustive process due to the requirement of sophisticated equipments for retaining particles in nanosize range. Apart from the above, surfactants essentially employed in the production of SLN increase solubility of the poorly soluble/insoluble drug in the external phase. This matter is of serious concern during production and upon long term storage as it results in progressive leaching of drug from the particles to external phase which results in reduced drug loading efﬁciency. The above issues have been discussed in detail in literature [12].The above discussion indicates that there is a necessity to develop a method which can separate the nanoparticles from the dispersion and immobilize them in order to retain their individual morphological identity upon storage. Harvesting the SLN from the nanodispersion by surface adsorption or retention on a submicron size inert pharmaceutical excipient with good ﬂowability, compressibility and adsorption capacity may be an excellent approach to overcome the above mentioned issues. The prepared “Adsorbed Lipid Nanoparticles” (ALN) would not only maintain the integrity of each adsorbed nanoparticle but also ease its ﬁlling into capsules or compression into tablet. To our knowledge, such a unique approach in the development of SLN delivery system has not been reported so far. However, limited studies involving the use of adsorbents to obtain lipid based granules for oral drug delivery have been reported wherein adsorbents were found to enhance the bioavailability of the drug and impart signiﬁcant ﬂow and compressibility to the ﬁnal blend [13–15].The drug employed here is carvedilol phosphate, a non-selective-blocker. The drug exhibits poor aqueous solubility and highlipophilicity (log P) which makes it an excellent candidate for SLN encapsulation[16,17]. A study conducted previously in our laboratory using different types and concentration of surfactants at different pH has shown that sodium taurocholate (STC) has both minimum molar solubilization capacity and binding constant for carvedilol phosphate at pH 7.2 [18]. Therefore, the objective of the present work was to develop SLN of carvedilol phosphate using STC as a stabilizing agent and pH 7.2 phosphate buffer as dispersion medium, and improve the physicochemical properties of the nanoparticles by adsorbing them onto Neusilin (magnesium aluminometasilicate), an inert pharmaceutical excipient used as adsorbent.
2. Materials and methods

[ Last edited by kaichang on 2011-1-9 at 13:15 ]

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kaichang

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Originally posted by kakarote at 2011-01-09 18:51:08:
The objective of the present study was to employ suitable adsorbent with free ﬂowing characteristicsfor improving the stability and physical properties of solid lipid nanoparticles (SLN) for ...

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