Solubility and dissolution enhancement of flurbiprofen by solid dispersion using hydrophilic carriers

1Department of Pharmaceutics, Max Institute of Pharmaceutical Sciences, Velugumatla, Wyra Road, Khammam, Telangana, India, 2Acharya Nagarjuna University, Nagarjuna Nagar, Guntur, Andhra Pradesh, India, 3Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research, Hyderabad, India, 4Department of Pharmaceutics, Chaitanya College of Pharmacy Education and Research, Hanamkonda, AP, India, 5Department of Pharmaceutics, Avanthi Institute of Pharmaceutical Sciences, Hayath Nagar, Ranga Reddy (D), Hyderabad, Telangana, India


INTRODUCTION
In the pharmaceutical industries, formulation scientists has a major challenge in the formulation of orally administered solid dosage forms is solubility enhancement and improvement of dissolution of poor water soluble drugs (Horter, Dressman, 2001).Solid dispersion technologies enhance the solubility and dissolution of drugs and thereby improve the oral bioavailability of poorly water soluble drugs (Patil, Gaikwad, 2009).Thus, drug's acceptability and bioavailability will depends on enhancement of solubility and dissolution that reduces dose required for showing fast onset of action (Chauhan, Shimpi, Paradkar, 2005).
Solid dispersions (SDs) are molecular dispersions of drug in the carriers and they were formulated by different methods, important are solvent evaporation and fusion (melt) method (Vippagunta, Maul, Tallavajhala, 2002).SD is a technique, in which drug is obtained as fine particles by dissolving the carriers in an aqueous fluids.It is a simple and flexible formulation process of obtaining solid dispersions without using toxic substances and enhances solubility and dissolution rate of drug (Bikiaris, 2011).
Flurbiprofen (FPN) is non-steroidal anti-inflammatory drug that belongs to BCS class II because of its poor water solubility (Veerareddy, Vemula, 2012).Different molecular weights of polyethylene glycols (PEG8000 and PEG10000) were used for the preparation of SDs.In this work, solvent evaporation method was employed for formulating FPN solid dispersions utilizing PEGs as carrier.

Material
Flurbiprofen was kindly gifted FDC Ltd., (Mumbai, India).PEG 8000 and PEG 10000 were gift samples from Central Drug House Pvt.Ltd., (Delhi, India).Crospovidone and Spray-dried lactose were obtained from Matrix laboratories Ltd., (Hyderabad, India).All other chemicals and reagents were purchased from S.D. Fine Chemicals, (Mumbai, India).

Phase solubility studies of FPN
An excess amount of FPN was taken into a flask containing aqueous solution (0, 5, 10, 15, 20, 25 and 30% w/v)of PEG 8000 and PEG 10000 separately (Suresh et al., 2013).The samples were continuously stirred on a stirrer for 48 h at room temperature.The samples were filtered by using 0.45 μm filter.Then clear filtrates were appropriately diluted and drug concentration was analysed byUV spectrophotometer at 247nm.
The solubilisation of drug in an aqueous solution was explained by Gibbs free energy of transfer (ΔG o tr ) and determined by equation given below.
where, S o /S s was FPN molar solubility ratio in PEGs solutions to that of water.

Preparation of FPN solid dispersions
Solvent evaporation method was employed to prepare FPNSD susing PEG8000 and PEG10000 as continuous phase in different weight ratios (Table I).PEGs and drug were dissolved in a round bottom flask containing 10 mLof ethanol.At a temperature not exceeding 45 °C, the solvent was evaporated in a vacuum oven.The resultant solid dispersions were grounded in a mortar with the help of pestle, kept in a vial and were stored in desiccators till further use (Christian, Jennifer, 2000).

Solubility studies
Solubility studies were performed for prepared SDs in various solvent systems (0.1 N hydrochloric acid, distilled water and pH 7.2 phosphate buffer).Excessive quantities of SDs were placed into a flask containing10 ml of each solvent.The flask was sonicated at 25 °C for 1 h, stirred and agitated for 2 days at 25 °C.The suspension was filtered using a 0.45 µm filter, diluted suitably and spectrophotometrically (UV-3200, LabIndia, Mumbai, India) analyzed at 247 nm.

Flow properties of powder
Angle of repose and Carr's compressibility index were used to determine the powder flow properties.Angle of repose (θ) was measured by fixed funnel method and it was determined by given formula: (1) where'θ' was angle of repose, 'h' and 'r' were height and radius of the cone of powder.
The tendency of a powder to be compressed can measured by Carr's index and determined using given below formula: (2) where 'ρ b 'and 'ρ p ' were bulk density and tapped density respectively.

Preparation of tablets
From the results of above studies, SD4 and SD8 formulations were prepared in oro dispersible tablets (ODTs) form (Table II).SDs equivalent to 50 mg of FPN and all other ingredients were sieved (# 60).Except lubricant and glidant, powder blend was mixed for 5 min.The powder blend was then lubricated for 2-5 min and compressed directly using rotary compression machine (CMD-3, Cadmach, Ahmedabad, India).In this way, conventional tablets were also prepared using 50 mg of pure FPN.

Characterization of tablets
The ODTs were characterized by different evaluation tests like weight variation, friability, hardness, disintegration, wetting time and drug content.All the tests were performed as per the procedure described in our previous work (Bhaskar, Rama, Sateesh, 2015).

In-vitro dissolution studies
The in-vitro dissolution studies of various FPN formulation (SD4, SD8, marketed and conventional formulations) was performed in USP Type II dissolution apparatus (TDL -08L, Electrolab, Mumbai, India) using 900 mL of phosphate buffer (pH 7.2) rotated at 50 rpm and maintained at 37.0±0.5 °C.Aliquots of 5 ml were withdrawn at pre-determined time intervals and the same amount of fresh dissolution media was replaced.The samples were analyzed by UV spectrophotometer at 247 nm after filtration through 0.45 µm filter and appropriate dilution.

Dissolution data treatment
Cumulative % drug release in 20 min (Q 20 ), mean dissolution time (MDT),dissolution efficiency (%DE) and relative dissolution rate (RDR) were determined to compare the optimized SDs with marketed tablets and conventional formulation of FPN as discussed in our previous article (Chella et al., 2016).

Drug-carrier compatibility studies
Drug-carrier interaction studies were performed using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and powder X ray diffraction (PXRD) studies.FTIR spectra of FPN, PEG and optimized SD were recorded on IR spectrophotometer (Shimadzu, Japan)in the range of 400 to 4000 cm -1 using pellets compacted by mixing approximately 5 mg of samples 100 mg of potassium bromide (KBr) under vacuum.The DSC thermograms of above said samples were recorded by placing approximately 5-10 mg sample in sealed aluminium pan with small openings on a differential scanning colorimetry(Shimadzu Corp., Japan), at a heating rate of 5 °C per min and a temperature from 0 to 400 °C under a flow of nitrogen gas.X-ray diffractometer (Siemens D5000, Texas, USA) was used to record the diffractograms.FPN, PEG 10000 and SD8 were exposed to Cu radiation

Stability studies
Stability of optimized formulation (SD8) was performed as mentioned in the literature (Mathews, 1999).The optimized ODTs were packed in aluminum paper and placed in the stability chamber for 6 months at 75±5% RH and 40±2 o .After completion of the storage period, in-vitro dissolution and assay were performed for collected samples.Paired t-test was performed to check the significant difference at p = 0.05.The similarity between before and after storage was determined by similarity index (F2) which indicates stability of optimized formulation.

Phase solubility studies
The results of phase solubility study presented in Table III indicate increase in FPN solubility linearly (R 2 = 0.970 with PEG 8000 and R 2 = 0.973 with PEG 10000) as the concentration of PEGs was increased.The phase solubility diagram is shown in Figures 1a and 1b.

Solubility studies of FPN SDs
Solubility studies of solid dispersion were performed in various solvent systems and the results are shown in Table IV.Solubility of FPN is higher in 7.2 pH phosphate buffer compared to 0.1N HCl and distilled water whereas, SDs showed more or less equal solubility in both water and phosphate buffer.The solubility of SDs increased with increase in concentration of carrier in both cases (PEG 8000 and PEG 10000).However,  SDs prepared with PEG10000 showed higher solubility in all concentrations compared to SDs prepared with PEG8000.Among all formulations, SD8 showed highest solubility in phosphate buffer pH 7.2 i.e., 0.561±0.02mg/mL.

Flow properties of powder
Angle of repose and Carr's compressibility index of the pure FPN and optimised formulations (SD4 and SD8) is reported in Table V.The angle of repose values lower than 30° and Carr's compressibility index less than 18 for two formulations indicates good flow properties for pure FPN and SDs.

Characterisation of tablets
The results of the tests performed were within the pharmacopoeial limits (Table VI).For the weight variation test, all the tablets were within 5% of average weight of tablets.The friability and hardness were found near to be 0.35% and 3.1kg/cm 2 for optimized SD8 formulation.The disintegration and wetting time of the optimized tablet were found to be 121 sec and 26 sec respectively, indicating rapid disintegration of optimised tablets.Tablets contain 99.24% of FPN.

In vitro dissolution studies
The ODTs containing PEG 10000 SD showed higher release of FPN compared with to ODTs containing PEG8000 SD, marketed and conventional tablets of plain FPN.The optimized formulation (SD8) containing PEG 10000 showed significantly improved (p<0.05) and faster drug release (99.08±1.35% in 20 min) compared with formulation SD4 containing PEG 8000 (93.67±1.12% in 20 min), marketed tablet (56.86±1.91%)and conventional tablet (47.31±0.74% in 20 min).The release pattern of FPN from various formulations is shown in Figure 2.

Treatment of dissolution data
The %FPN release from optimized formulation   (SD8) was significantly higher compared to conventional tablets in 20 min.DE(%), MDT, and RDR were determined.DE(%) was found to be 61.63% and MDT was reduced to 8.79 min compared with conventional tablet (23.71±1.46%and 25.76 min respectively).The relative dissolution rate of optimized SD8 formulation was found to be 2.09.

Drug-carrier compatibility studies
FT IR spectra of pure FPN, PEG 10000 and optimised formulation SD8 is shown in Figure 3.FTIR spectra of FPN exhibits prominent peaks at 2998.43 cm -1 (C-H stretching vibration), 1463.51 cm -1 (C-H bending vibration), 1721.37 cm -1 (C=O carbonyl stretch of acid), 1576.24cm -1 (C=C stretching of aromatic ring) and 1236.63 cm -1 (C-F stretching).Presence of all the principal peaks of FPN in SD8 formulation and absence of new peaks indicated that interaction was not present between the FPN and PEG 10000.
DSC thermograms obtained for pure FPN, PEG 10000 and SD8 solid dispersion are presented in Figure 4.The thermogram of FPN showed a sharp endothermic peak at 113.4 o characteristic of its melting point, whereas thermogram of the SD8 formulation showed broad endothermic peak of drug, indicating that FPN was molecularly dispersed in carrier.
The X-ray diffractograms of pure FPN, PEG 10000

Stability studies
Stability of the optimised formulation (SD8) was evaluated at accelerated condition.In-vitro dissolution studies and assay were performed after the completion of storage period.There was no significant variation i.e., p>0.05 in concentration of drug (Table VIII) determined by using paired t-test.Similarity index value was found to be 89.59.

DISCUSSION
The intent of current work is to study the role of hydrophilic carriers (PEG 8000 and PEG 10000) in improving the solubility and dissolution rate of FPN at different concentrations.FPN SDs were prepared by solvent evaporation method using PEG 8000 and PEG 10000 at four different concentrations of FPN to PEG and optimised SD was compressed into ODTs.Finally, solubility and dissolution rate of FPN from ODT containing SD was compared with that of marketed formulations and conventional tablets prepared with pure FPN.Linear increment in solubility of FPN was observed with increase in concentration of PEGs.As the calculated slopes were less than one, the phase solubility diagram follows an A L -type of solubility diagram (Suresh et al., 2013).Negative values of ΔG°t r (Gibbs free energy transfer) indicated that spontaneous solubilisation of FPN and it was decreased as the concentration of PEGs increases, indicating more favourable reaction with increase in concentration of PEGs.
Solid dispersions of FPN were prepared using various concentrations of PEG 8000 and PEG 10000 separately.In presence of PEG the solubility was increased up to drug to carrier ratio 1:4.Further increase in ratio to 1:5 and 1:6 did not show any significant improvement in the solubility.Hence, the formulations up to 1:4 ratios were included in the present study.Similar types of results were reported by Chauhan et. al., (Chauhan, Shimpi, Paradkar, 2005).The solubility of FPN from SDs prepared with PEG 10000 showed higher solubility compared with PEG 8000.Among all formulations, SD8 showed higher solubility in phosphate buffer pH 7.2.
Angle of repose and Carr's compressibility index were determined to find out the flow behaviour of powder.The angle of repose (<30°) and Carr's compressibility index (<18) values indicated that the powder blend has good flow property.Then FPN solid dispersions (SD1 to SD8) were compressed into orodispersible tablets (ODTs) based on the solubility data.Prepared ODTs were evaluated for various pharmacopoeial and other general tests like weight variation, hardness, friability, disintegration time, wetting time and drug content.All the tests were within the pharmacopoeial limits.
In vitro dissolution studies showed, ODTs containing PEG 10000 SDs showed higher release of FPN compared with ODTs containing PEG8000, marketed and conventional tablets.All the formulations containing FPN in the form of SDs showed higher drug release compared to marketed tablets and conventional tablets containing plain FPN.Formulation SD5 (with FPN to drug PEG 10000 ratio 1:1) showed complete drug release in 45 min.SD6 and SD7 formulations with FPN to drug PEG 10000 ratio 1:2 and 1:3 respectively showed complete drug release in 30 min.These values were higher than the results reported by Dong et al. (2011), who reported only 70% drug release in 60 min (Dong et al., 2011).Whereas, Formulation SD8 containing PEG 10000 of 1:4 ratio showed faster drug release (99.08±1.35% in 20 min) with significantly improved dissolution (p<0.05)compared with all other formulations (Figure 2).As the selected drug belongs to NSAID that needs to produce faster action we selected SD8 as final optimised formulation.
From in vitro dissolution studies it was evident that enhancement in dissolution rate was observed with tablets containing PEG 10000 compared with PEG 8000.It may be due to greater carrier solubilization effect, increased dispersibility and wettability of drug, increased dissolution in hydrophilic carrier, change in state of drug (may be amorphous form), decrease in crystallinity and/or a combination of the above said mechanisms (Dordunoo, Ford, Rubisteins, 1991).
The % flurbiprofen release (Q 20 ) from formulation SD8 was significantly higher compared to conventional tablets in 20 min.Enhancement in dissolution rate of a drug supported by mean dissolution time (MDT), dissolution efficiency (DE), and relative dissolution rate (RDR).DE was observed as 61.63% and it was increased almost by 3.0 folds from SD8 ODT compared with conventional tablets.MDT for SD8 formulation was reduced to 8.79 min, compared with conventional tablet (25.76 min).The relative dissolution rate (RDR) of optimized SD8 formulation was found to be 2.09.These results demonstrated that faster release of FPN from SD8 formulation compared to SD4, marketed and conventional tablets.
FTIR spectra showed no interaction between FPN and PEG, as same principal peaks present in pure drug and optimised SD8 formulation.The results of DSC studies revealed that, the sharp endothermic peak of drug was broadened in optimised SD8 formulation indicating FPN was molecularly dispersed in carrier.XRD studies showed the sharp intense peaks of drug indicating FPN was in crystalline state.The decrease or disappearance of peaks intensity in optimised SD8 formulation indicated, either there is a reduction in the crystallinity of FPN or it has undergone solid state transition to amorphous form.
Stability studies of the optimised SD8 formulation was performed at accelerated condition.No significant variation (p>0.05) in concentration of drug was observed, when determined using paired t-test.Similarity index value of 89.59 indicated that the similarity in dissolution profile of freshly prepared and after storage of optimised SD8 formulation.

CONCLUSIONS
An attempt was made to enhance the solubility and dissolution of FPN using SDs of PEG.In vitro dissolution rate of formulations with PEG10000 manifested best results compared with formulations with PEG 8000.Significant improvement (p<0.05) in percent drug release (Q 20 ) was observed with SD8 compared with SD4, marketed and conventional tablets containing pure drug.Enhancement in dissolution of FPN was observed possibly due solubilisation of drug in hydrophilic carrier or change in the crystallinity of the drug.The DE and MDT of SD8 formulation were also significantly improved compared with conventional tablets.In conclusion, formulation of PEG solid dispersions in less carrier ratio could be an alternative technique for enhancing solubility, dissolution and thereby improving the absorption of poor water soluble drugs like FPN.

FIGURE 2 -
FIGURE 2 -Cumulative% drug release of FPN from various formulations.

TABLE I -
Formulation of FPN solid dispersions using PEGs

TABLE II -
Composition of selected FPN SDs tablets of wavelength 1.540 Å, 40 KV voltage 30 mA current and analysed over the 2θ range of 2 o to 50°.

TABLE III -
Phase Solubility data of FPN in different concentrations of PEG 8000 and PEG 10000 aqueous solutions (Mean ± SD, n=3)

TABLE IV -
Solubility of FPN and its SDs (Mean± SD; n=6)

TABLE V -
Flow properties of FPN and formulations (Mean ± SD, n=3)

TABLE VI -
Physical