Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles

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1 Suvarna et al: Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles 2779 International Journal of Pharmaceutical Sciences and Nanotechnology Volume 8 Issue 1 January March 2015 Research Paper MS ID: IJPSN KISHAN Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles G. Suvarna, D. Narender and V. Kishan 1 * Department of Pharmaceutical Sciences, Laboratory of Nanotechnology, University College of Pharmaceutical Sciences, Kakatiya University, Warangal, Telangana , India. Received December 5, 2014; accepted December 23, 2014 ABSTRACT Rosuvastatin calcium (RC), is a hypolipidemic drug, and has poor oral bioavailability of about 20% due to first-pass effect. For improving the oral bioavailability of RC, solid lipid nanoparticles (SLNs) were developed using triglycerides (tristearin, tripalmitin, and trimyristin). Hot homogenization followed by ultrasonication method was used to prepare RC-SLNs. The prepared SLNs were characterized for particle size, PDI, zeta potential (ZP), entrapment efficiency (EE) and drug content. In vitro release studies were performed in 0.1N HCl and ph 6.8 phosphate buffer of by open tube method. Physical stability the SLNs was observed at refrigerated temperature and room temperature for 60 days. Pharmacokinetics of RC- SLNs after oral administration, in male Wistar rats was studied. SLNs prepared with tristearin (Dyanasan-118) having size of ± 8.52 nm, PDI of ± 0.084, ZP of 20.9 ± 4.88 mv with ± % EE were optimized. Differential scanning calorimetric (DSC) study revealed that no interaction between drug and lipid. In vitro release studies showed that more cumulative release of RC in ph 6.8 phosphate buffer than in 0.1NHCl during 24 hours. The lyophilized SLN formulation was used in knowing morphology of SLNs and was found to have spherical shape with increased polydispersity by Scanning electron microscopy. Pharmacokinetic studies showed the relative oral bioavailability of SLNs was 2.2 fold when compared to that of a suspension (p<0.001). Taken together, the results are indicative of SLNs as lipid based carriers for improving the oral bioavailability of this drug by minimizing first pass metabolism. KEYWORDS: Rosuvastatin calcium; Solid lipid nanoparticles; Triglycerides; Oral bioavailability; Pharmacokinetics. Introduction Oral route of drug delivery offers challenges for drugs having poor solubility, chemical instability in the gastrointestinal tract, poor permeability through the biological membranes or sensitivity to metabolism. The limiting factors of the oral bioavailability of drugs include first-pass metabolism, permeability, lack of the drug solubility and dissolution. Poorly soluble compounds tend to be eliminated from the GIT before they had opportunity to fully dissolve and absorb into the circulation. The inherent problems associated with the drug, in some cases, can be solved by modifying the formulation or changing the routes of administration. Controlled release behavior of colloidal systems is reported to enable the bypass of gastric and intestinal degradation of the encapsulated drug and their possible uptake and transport through the intestinal mucosa (Arik and Amnon, 2008). Absorption of nanoparticles occurs through mucosa of the intestine by several mechanisms, namely through the Peyer s patches, by intracellular uptake or by the paracellular pathway (Üner M and Yener G, 2007). Solid lipid nanoparticles (SLNs) are an alternative nanoparticulate carrier system to polymeric nanoparticles, liposomes and o/w emulsions (Mehnert W and Mäder K, 2001; Müller RH et al., 1995; Müller RH et al., 2000). Aqueous SLN dispersions are composed of lipid which is solid both at body and room temperature, being stabilized by a suitable surfactant. SLNs possess distinct advantages compared to other carriers, e.g., polymeric nanoparticles, lipids used in topical and oral drug delivery can be used as matrix material, including the long list of different surfactants/ stabilizers employed in these traditional formulations. Thus, there is no problem with the regulatory accepted status of excipients (Souto EB et al., 2007). Lipid nanoparticles were studied for percutaneous drug delivery (Driscoll MC, 2002; Souto EB and Müller RH, 2007; Müller RH et al., 2005). SLNs also enjoy more advantages over other colloidal delivery systems with regard to biocompatibility, scale up and also the release of drugs from SLNs can be modulated in order to optimize their performance (Zur Mühlen A et al., 1998). These features make lipid nanoparticles an interesting carrier system for optimized oral delivery of drugs. There are very few reports in literature describing the use of SLNs for bypassing first pass metabolism. When alltrans-retinoic acid was loaded into SLNs, the oral bioavailability in rats was increased four to five fold 2779

2 2780 Int J Pharm Sci Nanotech Vol 8; Issue 1 January March 2015 compared with that of suspension (Hu L et al., 2004). The oral bioavailability of Cryptotanshinone was increased by incorporating into SLNs (Lian Dong Hu et al., 2010). The pharmacokinetics and tissue distribution aspects of clozapine loaded solid lipid nanoparticles after intraduodenal administration was studied (Manjunath K and Venkateswarlu V, 2005). Rosuvastatin calcium (RC), is an antilipedemic agent that competitively inhibits hydroxyl methyl glutarylcoenzyme A (HMG-CoA) reductase. It exhibits poor oral bioavailability of about 20% due to first-pass hepatic metabolism. To overcome hepatic first-pass metabolism, insolubility of drug and to enhance oral bioavailability, lipid based drug delivery systems (solid lipid nanoparticles) can be exploited. These systems enhance the lymphatic transport of the lipophilic drugs, it may increase the solubility of drug and therefore increase the bioavailability. In the present study, solid lipid nanoparticles are employed to incorporate RC to bypass the drug from first pass metabolism, thereby to increase its bioavailability, reduce the dose and to improve activity. Materials Rosuvastatin calcium was obtained as a gift sample from Aurobindo Labs, Hyderabad, India. Trimyristin (Dynasan-114), Tripalmitin (Dynasan-116) and Tristearin (Dynasan-118) were purchased from Sigma-Aldrich Chemicals, Hyderabad, India. Egg Lecithin E-80 was gift sample from Lipoid, Germany. Poloxamer-188 was gift sample from Aurabindo Labs, India. Methanol, acetonitrile, chloroform were of HPLC grade (Merck, India). Centrisart filters (molecular weight cut off 20,000) were purchased from Sartorius, Goettingen, Germany. Methods Preparation of SLNs RC loaded SLNs were prepared by hot homogenization followed by the ultrasonication method (Müller RH et al., 2000). The composition of various formulations is shown in Table 1. RC, solid lipid and emulsifier (egg lecithin) were dissolved in 10 ml of a mixture of methanol and chloroform (1:1). Organic solvents were completely removed using a rotary flash evaporator. The embedded lipid layer was molten by heating to 5 C above the melting point of the lipid. An aqueous phase was prepared by dissolving the stabilizer (poloxamer 188) in distilled water (1.5% w/v) and heating to the same temperature of the oil phase. The hot aqueous phase was added to the oil phase and homogenization was performed (at rpm) using a homogenizer (DIAX 900, Germany) for 5 minutes. The coarse oil in water emulsion so obtained was sonicated using a probe soincator (Vibracell, USA; 12T-probe) for 20 min. RC loaded SLNs were finally obtained by allowing the hot nanoemulsion to cool to room temperature. Preparation of rosuvastatin calcium suspension About 50 mg of sodium carboxy methyl cellulose (suspending agent) was taken in a mortar and triturated for 3 min, then 10 mg of rosuvastatin calcium was added to it and triturated for 3 min. To it, 10 ml of water was added and again triturated for 5min to form rosuvastatin calcium suspension (Table 1). Characterization of SLNs Drug-excipient compatibility studies by differential scanning calorimeter (DSC) DSC is one of the basic techniques used to investigate drug-excipient compatibility. DSC of pure drug, pure lipid (Dynasan-118) and optimized formulation was performed by Mettler-Toledo DSC 821e (Columbus, OH) instrument at a heating rate of 10 o C/min in the temperature range of o C. DSC was calibrated by using indium. Measurement of Particle Size, PDI and Zetapotential of SLNs The prepared solid lipid nanoparticle preparations were diluted in 1:50 ratio with double distilled water and size was measured at 90 angles by Malvern zeta sizer (Nano ZS90). The average particle size, polydispersity index and zeta potential were obtained directly from the instrument. TABLE 1 Compositions of RC loaded SLNs with different lipids Formulation ingredient Formulation code F1 F2 F3 F4 F5 F6 F7 ORGANIC PHASE RC (mg) Dynasan-114 (mg) Dynasan-116 (mg) Dynasan-118 (mg) Egg lecithin (mg) Chloroform : Methanol (1:1) (ml) AQUEOUS PHASE RC (mg) Sodium carboxy methyl cellulose (mg) Poloxamer-188 (mg) Double distilled water (ml)

3 Suvarna et al: Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles 2781 Measurement of entrapment efficiency (EE) Entrapment efficiency was determined by measuring the concentration of free drug (un-entrapped) in aqueous medium (Vinay Kumar V et al., 2012). The aqueous medium was separated by ultra-filtration using centrisart tubes (Sartorius, USA) which consisted of filter membrane (M.Wt. cut off 20,000 Da) at the base of the sample recovery chamber. About 2.5 ml of the formulation was kept in the outer chamber and sample recovery chamber was placed over the sample and centrifuged at 4000 rpm for 15 min. The SLN along with the encapsulated drug remained in the outer chamber and aqueous phase moved into the sample recovery chamber through filter membrane. The amount of RC in the aqueous phase was estimated by HPLC. Determination of total drug content About 100 μl of the formulation was dissolved in 0.9 ml of chloroform and methanol mixture (1:1) and then further dilutions were made with mobile phase. The diluted samples were estimated by HPLC for the total amount (Vinay Kumar V et al., 2012) of RC present. In vitro drug release studies Dialysis method was used to perform in vitro release studies. Dialysis membrane (Himedia, India) having a pore size of 2.4 nm and molecular weight cut-off between 12,000 14,000 was used for the release studies. Dialysis membrane was soaked overnight in double distilled water prior to the release studies (Narendar D and Kishan V, 2014). Hydrochloric acid (0.1N) and phosphate buffer ph 6.8 were used as release media. The experimental unit had donor and receptor compartments. Donor compartment consisted of a boiling tube which was cut open at one end and tied with dialysis membrane at the other end into which 1 ml of SLN dispersion was taken for release study. Receptor compartment consisted of a 250 ml beaker which was filled with 100 ml release medium and the temperature was maintained at 37 ± 0.5 C. At 0.25, 0.5, 1, 2, 3, 4, 6, 8, 10, 12 and 24 hour time points, 1 ml samples were withdrawn from receiver compartment and replenished with the same volume of release medium. The collected samples were suitably diluted and analyzed by UV-Visible Spectrophotometer (SL-150, ELICO) at 243 nm (Sevda RR et al., 2011). Physical stability of SLNs under storage Physical stability study of RC loaded solid lipid nanoparticles for optimized formulation F5 was conducted by storing at room and refrigerated temperature for 60 days and average size, zeta potential and poly dispersity index were determined. Lyophilization of SLNs The optimized SLN formulation containing 10% w/v lactose was prepared and kept in a deep freezer at 40 o C (Sanyo, Japan) for overnight. The frozen samples were then transferred into freeze-dryer (Lyodel, Delvac Pumps Pvt. Ltd, India). Vacuum was applied for about 48 hr to get powdered lyophilized product (Schwarz and Mehnert, 1997). Free flowing powder was used for measurement of size, PDI, ZP after reconstitution and surface morphology study. Surface morphology study by scanning electron microscopy (SEM) The size and morphology of nanoparticles was studied by Scanning Electron Microscope (SEM, Hitachi, Japan). Lyophilized solid lipid nanoparticles of rosuvastatin calcium (F5) were suitably diluted with double distilled water (1 in 100) and a drop of nanoparticle dispersion was placed on sample holder and air dried. Then the sample was observed at accelerating voltage of volts at various magnifications. Imaging was carried out in high vacuum (Vijaykumar N et al., 2009). Pharmacokinetic studies of the rosuvastatin calcium SLNs and suspension in male albino wistar rats The study objective was to find out the bioavailability of optimized rosuvastatin calcium SLN preparation, F5 and comparing with that of rosuvastatin calcium suspension F7. The study was conducted with prior approval of Institutional Animal Ethical Committee. The male albino Wistar rats weighing gm were divided into two groups (n = 6) and were orally administered with preparation (F5) and suspension (F7) at a dose of 5mg/kg body weight. At pre-determined time intervals, blood samples were collected (0.5, 1, 2, 4, 8, 12, 24 and 48 hr) by puncturing the retro-orbital venous plexus. The blood was allowed to clot, centrifuged at 4000 rpm for 15 mins and serum was collected. The serum was stored at 20 o C until analysis. Extraction procedure of rat serum samples containing rosuvastatin calcium To 100 µl of serum, 10 µg/ml of naproxen (Internal standard) was added and vortexed for 5 min, after that 200 µl of methanol was added, and then further vortexed for 5 min. The mixtures were centrifuged at 3000 rpm for 30 min at 4 C temperature. The supernatant samples were collected and analyzed using HPLC (LC 10AT, Shimazdu, Japan) with UV-detector (SPD 10A, Shimadzu, Japan). HPLC conditions: Chromatographic conditions Mobile phase : Acetonitrile: 0.2% tri ethyl amine buffer (60:40) Flow rate : 1mL/min Column : Lichrospher C18 (250 mm X 4.6 mm i.e., 5 µm particle size) Column temperature : 25 C Injection volume : 20 µl UV detection : 284 nm Detector sensitivity : AUFS Retention time : 4.3 min Calculation of pharmacokinetic parameters The concentrations of rosuvastatin calcium in rat serum samples were obtained from the calibration curve prepared. The pharmacokinetic parameters Cmax, Tmax, AUC0-24 and t1/2 were calculated by Kinetica software, 2000.

4 2782 Int J Pharm Sci Nanotech Vol 8; Issue 1 January March 2015 Statistical treatment of data The statistical comparison of data was done using unpaired t-test by Graph pad prism software (version 5.0, 2007), significance was calculated at p-value of Results and Discussion Measurement of particle size, PDI, zeta potential, entrapment efficiency and assay The solid lipid nanoparticles were prepared by homogenization followed by ultra sonication for different formulations i.e., F1-F6. All the prepared samples were analyzed in order to determine their particle size, zeta potential and PDI values. The results are presented in Table 2. The particle size of all the formulations ranged from ± 1.87nm to ± 4.92nm, PDI from ± to ± and zeta potential from 11.7 ± 4.64 to 22.5 ± 7.59 mv. From the results obtained, formulations containing Dynasan-114 (F1 and F2) showed relatively lower particle sizes, but the PDI was higher and zeta potential was lower. Formulations containing Dynasan-116 showed high PDI, but lower zeta potential (F3 and F4), where as formulations containing Dynasan-118 showed higher particle size, lower PDI and higher zeta potential (F5 and F6) when compared to other formulations. Entrapment efficiency and drug content TABLE 2 Physical characters - Size, PDI, ZP, assay and EE (%) of RC-SLNs (n=3) Formulation code Size (nm) PDI Zeta potential (mv) Assay (mg) All the formulations were analyzed for entrapment efficiency and drug content by HPLC and the results are shown in Table 2. From the results obtained, all formulations showed entrapment efficiency ranging from ± 0.10% to ± 0.21% and formulation containing Dynasan-118 showed slightly higher values when compared to Dynasan-114 and Dynasan-116, which is not significant statistically. In all these cases, EE was not increased with increments in the lipid concentration. Total drug content in the SLN formulation was determined to be 9.63 ± 0.01mg to ± 0.01mg. In vitro release studies In vitro release studies were performed for all formulations in 0.1N HCl and ph 6.8 phosphate buffer (Figure 1 and Figure 2) for 24 hr. Formulations containing Dynasan-114, Dynasan-116 and Dynasan-118 showed cumulative drug release ranging from ± 1.91% to ± 0.27%, ± 2.49% to ± 1.93% and ± 2.14% to 64.2 ± 0.09% respectively in 0.1N hydro-chloric acid. Formulations containing Dynasan-114 (F1 and F2) showed cumulative drug release ranging from ± 0.45 % to ± 1.03% in ph 6.8 phosphate buffer. Formulations containing Dynasan-116 (F3 and F4) showed drug release ranging from ± 1.44% to ± 1.34% in 6.8 ph phosphate buffer. Formulations containing Dynasan-118 (F5 and F6) showed drug release ranging from ± 2.41% to ± 0.86% in 6.8 ph phosphate buffer. Entrapment efficiency (%) F ± ± ± ± ± 0.10 F ± ± ± ± ± 0.24 F ± ± ± ± ± 0.30 F ± ± ± ± ± 0.10 F ± ± ± ± ± 0.21 F ± ± ± ± ± 0.25 Fig. 1 Over lay of DSC thermograms of (a) Rosuvastatin calcium, (b) Dynasan-118 and (c) Optimized formulation (F5).

5 Suvarna et al: Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles 2783 Fig. 2 Cumulative % drug release from rosuvastatin calcium SLNs in 0.1N HCl. (Note: SD bars are not visible, n = 3) When compared, the cumulative release in 0.1NHCl medium was less than that of 6.8 ph phosphate buffer. This difference in cumulative release could be due to the solubility differences of drug in these release media. Even though F6 SLN showed maximum release, but F5 was selected as optimized formulation for further studies, since there was no significant difference in release while there was increase in lipid content by 50%. Formulation (F5) containing Dynasan-118 showed release of ± 2.41% in 6.8 ph phosphate buffer for a period of 24 hours. Due to increased lipid content, the release was significantly retarded in all the prepared SLNs when compared in each set. Drug-excipient compatibility studies by DSC DSC studies of drug, pure lipid and optimized formulation are shown in Fig. 3. The DSC thermogram of Rosuvastatin calcium exhibited a sharp endothermic peak at C. The DSC thermogram of Dynasan-118 showed a sharp endothermic peak at C. The DSC thermogram of optimized formulation (with Dynasan 118) showed broader peaks at C and C for lipid and drug respectively. The peak positions were shifted slightly to lower side in formulation when compared to peaks of pure drug and Dynasan-118. No new peak was observed. Hence, this indicated that no interaction occurred between drug and lipid used during SLN formulation. Stability studies Stability studies were conducted for finally optimized formulation (F5) at room temperature and refrigerated temperature for 2 months. Some changes were noticed in size and zeta potential values but statistically insignificant (Table 3), which indicated the susceptibility for stability problems during storage at room temperature and 4 o C. Lyophilization of SLNs Lyophilized SLN powder was diluted with (1 in 50) double distilled water and measured the size, PDI and ZP. Size, PDI and ZP was found to be nm, 0.344, 20.9 mv and nm, 0.692, 24.8 mv before and after lyophilization, respectively. This might be due to the aggregation of smaller SLN particles resulting in large particles due to overall freeze-drying process. Surface morphology of SLN by scanning electron microscopy SEM studies were performed for the optimized formulation (F5) to determine the surface morphology of the SLN at two magnifications, 2000X and 8000X. The particles appeared to have mostly spherical shape (Fig. 4). The size of the particles increased. Due to lyophilization, the particles got aggregated and as a result size of the particles increased and was also reported earlier (Mäder K and Müller RH, 2000). In vivo bioavailability studies In vivo bioavailability study was performed for optimized (F5) formulation and suspension (F7) in male Wister rats. Various pharmacokinetic parameters obtained for both suspension and SLN preparation, following oral administration are given in Table 4. With suspension, the average peak plasma concentration, Cmax of RC was ± μg/ml, whereas in the case of SLN, the peak plasma concentration was ± μg/ml. The tmax is same for both suspension and SLN. The plasma concentration-time profiles of suspension and SLN formulation are shown in Fig. 5. It was found that Cmax and AUC0-24, for suspension (F7) was lower than that of the optimized SLN formulation (F5). The relative oral bioavailability of the SLN formulation (F5) was found to be 2.2 folds more than that of suspension (F7). This might be due to lymphatic transport of drug from SLN formulation and the level of significance was found to be p<0.001.

6 2784 Int J Pharm Sci Nanotech Vol 8; Issue 1 January March 2015 Fig. 3 Cumulative % drug release from rosuvastatin calcium SLNs in ph 6.8 phosphate buffer (Note: SD bars are not visible, n = 3) TABLE 3 Effect of storage at refrigerated temperature and room temperature on Size, PDI and Zeta potential of optimized (F5) SLN formulation (mean±sd, n = 3) Day At room temperature At refrigerated temperature Size (nm) PDI ZP (mv) Size (nm) PDI ZP (mv) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.12 Fig. 4 SEM images of lyophilized RC-SLN (F5) formulation at two magnifications (left panel X and right panel X) showing spherical shape. TABLE 4 Pharmacokinetic parameters of RC after oral administration of optimized SLN formulation (F5) and Suspension (F7) (mean ± SD, n = 6) Parameter F5 F7 Cmax (µg/ml) ± # ± tmax (h) 2 ± ± 0.00 AUC(0-24) (µg/ml)h ± 0.18 # ± 0.19 t1/2 (h) ± ± 0.83 MRT (h) ± ± 0.49 Note: # Significant at p<0.001 when compared with control F7

7 Suvarna et al: Preparation, Characterization and In vivo Evaluation of Rosuvastatin Calcium Loaded Solid Lipid Nanoparticles 2785 Fig. 5 Serum concentration Vs time profile of rosuvastatin calcium upon oral administration of two formulations (F5 and F7) to male wistar rats Conclusions Rosuvastatin calcium is a poorly water soluble drug with oral bioavailability of 20% due to extensive first pass metabolism. SLNs were prepared by hot homogenization followed by ultra sonication method. All the six SLNs were prepared with three lipids, each at two different concentrations. Characterization of SLNs was done by measuring particle size, poly dispersity index and zeta potential by zeta sizer. By formulating the rosuvastatin calcium solid lipid nanoparticles, an increase in oral bioavailability by 2.2 times than a control suspension was observed. Probably, due to overcoming the effect of first pass metabolism by following lymphatic transport pathway. Acknowledgements First two authors thank the AICTE, New Delhi for providing financial assistance in the form of Scholarship. We thank M/s Aurobindo labs, Hyderabad, India for providing the gift sample of rosuvastatin calcium. References Arik Dahan and Amnon Hoffman (2008). Rationalizing the Selection of Oral Lipid based Drug Delivery Systems by an in vitro Dynamic Lipolysis Model for Improved Oral Bioavailability of Poorly Water Soluble Drugs. J Contr Rel 129: Driscoll MC (2002). Lipid-based Formulations for Intestinal Lymphatic Delivery. Eur J Pharm Sci 15: Hu L, Tang X and Cui F (2004). Solid Lipid Nanoparticles (SLNs) to Improve Oral Bioavailability of Poorly Soluble Drugs. J Pharm Pharmacol 56: Lian Dong Hu, Qianbin Xing, Jian Meng and Chuang Shang (2010). Preparation and Enhanced Oral Bioavailability of Cryptotan- Shinone Loaded Solid Lipid Nanoparticles. AAPS Pharm SciTech 11(2): Mäder K and Müller RH (2000). Influence of Different Parameters on Reconstitution of Lyophilized SLN. Int J Pharm 196: Manjunath K and Venkateswarlu V (2005). Pharmacokinetics, Tissue Distribution and Bioavailability of Clozapine Solid Lipid Nanoparticles after Intravenous and Intraduodenal Administration. J Contr Rel 107: Mehnert W and Mäder K (2001). Solid Lipid Nanoparticles Production, Characterization and Applications. Advanced Drug Delivery Reviews 47: Mühlen AZ, Schwarz C and Mehnert W (1998). Solid Lipid Nanoparticles (SLN) for Controlled Release Drug Delivery Drug Release and Release Mechanism. Eur J Pharm Biopharm 45: Müller RH, Mehnert W and Lucks JS (1995). Solid Lipid Nanoparticles (SLN) An Alternative Colloidal Carrier System for Controlled Drug Delivery. Eur J Pharm Biopharm 41: Müller RH, Mehnert W and Sven G (2000). Solid Lipid Nanoparticles (SLN) for Controlled Drug Delivery - A Review of the State of the Art. Eur J Pharm Biopharm 50: Müller RH, Mehnert W and Souto EB (2005). Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC) for Dermal Delivery. In: Bronaugh RL, Maibach HI, (Eds). Percutaneous Absorption: Drugs, Cosmetics, Mechanisms, Methods (Drugs and the Pharmaceutical Sciences). Marcel Dekker: New York Narendar D and Kishan V (2014). Candesartan Cilexetil Loaded Solid Lipid Nanoparticles for Oral Delivery: Characterization, Pharmacokinetic and Pharmacodynamic Evaluation. Drug Delivery Early Online: DOI: / Schwarz C and Mehnert W (1997). Freeze-Drying of Drug-Free and Drug-Loaded Solid Lipid Nanoparticles (SLN). Int J Pharm 157: Sevda RR, Ravetkar AS and Shirote PJ (2011). UV Spectrophotometric Estimation of Rosuvastatin Calcium and Fenofibrate in Bulk Drug and Dosage form using Simultaneous Equation Method. Int J ChemTech Res 3(2): Souto EB and Müller RH (2007). Lipid Nanoparticles (Solid Lipid Nanoparticles and Nanostructured Lipid Carriers) for Cosmetic, Dermal and Transdermal Applications. In: Thassu D, Deleers M, Pathak Y (Eds) Nanoparticulate Drug Delivery Systems: Recent Trends and Emerging Technologies. CRC Press Souto EB, Almeida AJ and Müller RH (2007). Lipid Nanoparticles (SLN, NLC) for Cutaneous Drug Delivery: Structure, Protection and Skin Effects. J Biomed Nanotech 3: Üner M and Yener G (2007). Importance of Solid Lipid Nanoparticles (SLN) in various Administration Routes and Future Perspectives. Int J Nano 2(3): Vijaykumar N, Raviraj P, Venkateshwarlu V and Harisudhan T (2009). Development and Characterization of Solid Oral Dosage form Incorporating Candesartan Nanoparticles. Pharm Dev Tech 14(3): Vinay Kumar V, Raghavendra C, Rojarani K, Laxminarayana A, Ramakrishna S and Prakash VD (2012). Design and Evaluation of Polymer Coated Carvedilol Loaded Solid Lipid Nanoparticles to Improve the Oral Bioavailability: A Novel Strategy to Avoid Intraduodenal Administration. Colloids Surf B 95: 1-9. Address correspondence to: Prof. V. Kishan, Dept of Pharmaceutics, University College of Pharmaceutical Sciences, Kakatiya University, Warangal, Telangana , India. Tel: ; Fax: vbkishan@yahoo.com

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