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International Journal of Pharmaceutics 465 (2014) 436–443

Contents lists available at ScienceDirect

International Journal of Pharmaceutics

journa l homepage: www.e lsev ier .com/ locate / i jpharm

harmaceutical Nanotechnology

reparation of osthole-polymer solid dispersions by hot-meltxtrusion for dissolution and bioavailability enhancement

ei Yuna, An Kanga, Jinjun Shanb, Xiaoli Zhaoa, Xiaolin Bia, Junsong Lia, Liuqing Dia,∗

School of Pharmacy, Nanjing University of Chinese Medicine, 138 Xianlin Street, Nanjing 210046, ChinaFirst College of Clinical Medicine, Nanjing University of Chinese Medicine, 138 Xianlin Street, Nanjing 210046, China

r t i c l e i n f o

rticle history:eceived 8 October 2013eceived in revised form 17 January 2014ccepted 23 February 2014vailable online 25 February 2014

eywords:stholeolid dispersion

a b s t r a c t

The aim of this study was to investigate the potential of solid dispersion to improve the dissolutionrate and bioavailability of osthole (Ost), a coumarin derivative with various pharmacological activitiesbut with poor aqueous solubility. In present studies, the Ost solid dispersions were prepared with var-ious polymers including Plasdone S-630, HPMC-E5, Eudragit EPO, and Soluplus by hot-melt extrusionmethod. In vitro characterizations were performed with differential scanning calorimetry (DSC), X-raypowder diffraction (XPRD), Fourier transform infrared (FT-IR) spectroscopy, and in vitro dissolution stud-ies. In addition, in vivo pharmacokinetic studies of Ost solid dispersions were also conducted in rats aftera single oral dose. In comparison to the untreated Ost coarse powder and the physical mixture with

ot-melt extrusionolubility parameterissolution rateioavailability

polymers, the solid dispersions prepared with Plasdone S-630 or HPMC-E5 (drug/polymer: 1:6) showeda significant enhancement of dissolution rate (∼3-fold higher D30). In addition, such preparations exhib-ited a significantly decreased Tmax, ∼5-fold higher Cmax and ∼1.4-fold higher AUC when comparing withOst coarse powder. In conclusion, solid dispersion prepared with appropriate polymer could serve as apromising formulation approach to enhance the dissolution rate and hence oral bioavailability of Ost.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Osthole, a coumarin derivative, is the major bioactive con-tituent isolated from the fruit of Cnidium monnieri (L.) Cusson.t has been widely used for the treatment of skin disease andynecopathy in Eastern Asians for hundreds of years. Modernharmacological studies have shown that Ost exhibited variousharmacological effects (He et al., 2012; You et al., 2009), includ-

ng anticancer (Xu et al., 2013), anti-osteoporosis (Ming et al.,011), anti-inflammation (Wei et al., 2012), anti-apoptosis (Hout al., 2009), and anti-allergic androgenic effects (Hsieh et al., 2004).ecently, Ost was reported to be effective for the treatment of alco-olic and milk-induced fatty liver disease (Du et al., 2011; Zhangt al., 2011). Although many pharmacological activities of Ost haveeen recognized, its aqueous solubility is relatively poor (intrinsicolubility estimated as 2 �g/ml). For such hydrophobic compound,oor solubility would resulted in a slow dissolution and hence low

nd erratic oral bioavailability, which may limit its further clinicalpplication. So far, only few formulation strategies for improvingissolution of Ost have been investigated. For instance, Liu et al.

∗ Corresponding author. Tel.: +86 25 85811230; fax: +86 25 83271038.E-mail address: diliuqing@hotmail.com (L. Di).

ttp://dx.doi.org/10.1016/j.ijpharm.2014.02.040378-5173/© 2014 Elsevier B.V. All rights reserved.

significantly enhanced the dissolution rate of Ost by preparationof hydroxypropyl-�-cyclodetrin inclusion complexes (Liu et al.,2010). On the other hand, there is no report about in vivo phar-macokinetic performance of Ost in formulation development tillnow.

Various approaches are available to improve dissolution rate ofpoorly water-soluble drug, including the use of surfactants (Schottet al., 1982), inclusion complexation (Ammar et al., 1996), drugmicronization into an amorphous form (Hancock and Zografi, 1997)and solid dispersion (Chiou and Riegelman, 1971). In the soliddispersion, the drug may be dispersed or solubilized within a poly-meric carrier at molecular levels or in the amorphous state, andprovide a large surface which significantly enhances the dissolu-tion process. The improvement in dissolution is mainly attributedto the reduction in particle size, increase in surface area and reduc-tion in crystallinity. Furthermore, no energy is required to breakup the crystal lattice of a drug during the dissolution process, anddrug solubility and wettability may be improved by surround-ing hydrophilic polymers used in solid dispersions (Shinde et al.,2008). In comparison with traditional methods for preparation of

solid dispersions, hot melt extrusion (HME), as a promising noveltechnology for improving the bioavailability of water-insolubledrugs, presents many advantages for pharmaceutical applications.It can be used as a continuous process with the absence of organic

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F. Yun et al. / International Journa

olvents and subsequent drying steps, which makes scaling-up eas-er (Djuris et al., 2013; Sarode et al., 2012). In addition, intenselending and agitation during process prevent the aggregation ofrug particles suspending in the molten polymer, leading to a moreomogeneous dispersion of fine particles (Feng et al., 2012). How-ver, not all the thermal plastic polymer carriers are compatibleith the drugs and suitable carriers as well we drug/polymer ratio

or a specific drug need to be optimized.In the present studies, we attempted to improve dissolution

nd bioavailability of Ost by preparation of solid dispersions withME technique. Hydrophilic polymers with different glass tran-

ition temperatures and backbones will be used to prepare solidispersions. Differential scanning calorimetry (DSC), X-ray powderiffraction (XRPD), Fourier transform infrared (FT-IR) spectroscopy,nd dissolution studies will be conducted to compare the in vitroharacterization and performance of prepared solid dispersionsith coarse Ost power and physical mixtures of Ost and polymers.

urther pharmacokinetics of Ost in rats was investigated to evaluatehe in vivo performance of prepared solid dispersions.

. Materials and methods

.1. Materials

Ost (purity >98%; Fig. 1A) was purchased from Xi’an Tianbenio-engineering Co. Ltd. (Xi’an, China). Ost standard and internaltandard (IS) imperatorin (Fig. 1B) were obtained from the Nationalnstitute for the Control of Pharmaceuticals and Biological Prod-cts (Beijing, China). Eudragit EPO and Plasdone S-630 were kindlyifted from Evonic Degussa Corporation (Piscataway, NJ, USA) andSP Technologies Inc. (Wayne, NJ, USA), respectively. Polyvinylaprolactam–polyvinyl acetate–polyethylene glycol graft copoly-er (Soluplus, BASF, Germany) and Hypromellose-E5 (HPMC)

Colorcon, Germany) were kindly donated from the manufactures.actose and Glucose were provided by GlaxoSmithKline (Ware, UK).

.2. Solubility parameter calculations

Solubility parameter (ı) for Ost was performed by the groupontribution method using molecular modeling pro softwareChemSW, Fairfield, CA, USA). The solubility parameters for theolymers (i.e. Eudragit EPO, Plasdone S-630, HPMC, Solupus, Lac-ose and Glucose) were taken from the literatures (Chokshi et al.,005; Djuris et al., 2013; Forster et al., 2001; Sathigari et al., 2012)nd matched to Ost by observing the relative difference in total,ı. The differences (�ı) between the ı values of the drugs and the

olymers were also determined.

.3. Preparation of hot-melt extrudates

Composites of drug and polymer at different ratios of 1:3,:6 and 1:9 were applied to prepare solid dispersions by theaake Minilab twin-screw extruder with counter rotating screws at5 rpm. The temperatures for processing were selected accordingo the glass transition temperature (Tg) of the polymers and meltingoint of the drug. Due to the different physicochemical character-

stics of the applied carriers, the temperature setting was varied tobtain a semi-solid, transparent strand for each formulation suit-ble for down-processing. In the present investigation, about 120,65, 85 and 105 ◦C was applied for Plasdone S-630, HPMC, EudragitPO and Soluplus to prepare polymer–drug hot-melt extrudates,

espectively. The homogeneous hot-melt extrudates were collectednd allowed to cool down to room temperature for at least 24 h, andhen pulverized to pass through a 60-mesh screen. The obtainedowder of Ost solid dispersions was stored in a dryer at room

armaceutics 465 (2014) 436–443 437

temperature for further in vitro physicochemical characterizationand in vivo pharmacokinetic evaluation.

2.4. Physicochemical characterization of solid dispersions

2.4.1. Drug contentDrug content in the prepared solid dispersions were analyzed

by a validated HPLC method. The HPLC system consists of a solventmanagement system (quaternary gradient mode), auto injector,column oven and a 4 channel in line degasser, a sample manage-ment system and a 2998 PDA detector (Waters Corporation, USA).Chromatographic separation was performed on a reversed-phaseC18 column (4.6 × 250 mm, 5 �m; Waters, USA) with an isocraticelution of methanol–water (80:20, v/v) at a flow rate of 1 mL/min.Absorbance was monitored at 320 nm. The column was maintainedat 30 ◦C and the injection volume was 10 �L. Data acquisition wasperformed by the Empower 3 software.

2.4.2. DSC studiesTo examine the effect of different polymers on the status of

crystallinity of Ost in the prepared solid dispersions, pure drugOst, each polymer, physical mixture of Ost and polymer, as well asprepared solid dispersions were investigated using DSC-204 instru-ment (Netzsch, Germany). Each sample was sealed in aluminumhermetic pans and heated from 40 ◦C to 200 ◦C at a heating rateof 10 ◦C/min in an atmosphere of nitrogen. Data analysis was per-formed using NETZSCH-Proteus software.

2.4.3. X-ray powder diffraction (XRPD)To determine the physical state of pure drug, XRPD of the pre-

pared solid dispersions and their binary physical mixtures wererecorded using D/max 2500 PC XRD analyzer (Rigaku Corporation,Tokyo, Japan) with a Cu-K� radiation source. Samples were gentlyplaced in an aluminum holder. The tube voltage and amperage wereset at 40 kV and 100 mA, respectively. Measurement was conductedin the 2� range from 3◦ to 60◦ using a 0.02◦ step size and 1◦/minscan speed.

2.4.4. FTIR studiesThe FTIR spectra of the pure drug Ost, each used polymer,

physical mixture of Ost and polymer, as well as the preparedsolid dispersions were investigated by Bruker-MPA FTIR system(BRUKKER, Switzerland). The samples were mixed with KBr andpellets were prepared in the FTIR holder. Spectra were performedin the transmission mode in the region 4000 to 400 cm−1 using theresolution 2 cm−1.

2.4.5. Dissolution testingThe dissolution studies of the coarse powder of pure drug Ost,

physical mixture (PM) of Ost and polymer, as well as the preparedsolid dispersions (each sample containing 4 mg of Ost) were per-formed using dissolution test method 2 as described in the ChinesePharmacopeia 2010. The dissolution medium was 900 mL of pH 4.5acetate buffer with 0.05% Tween 80. The temperature of dissolu-tion medium was set at 37 ◦C and the paddle rotation speed wasadjusted to 50 rpm. Samples (10 ml) were withdrawn at 5, 10, 20,30, 45, 60, 90 and 120 min, filtered through a 0.45-�m Milliporefilter, and analyzed by the HPLC method described above.

2.5. Pharmacokinetic study

2.5.1. Animals

Male Sprague-Dawley rats (180–220 g) were obtained from the

Laboratory Animal Center of Nanjing Medical University (Nanjing,China). The rats were housed in an environmentally controlledbreeding room (temperature maintained at 24 ± 2 ◦C and with a

438 F. Yun et al. / International Journal of Pharmaceutics 465 (2014) 436–443

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1lAdt

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fitRPtcp6tL2

cda

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tcf2atuer1

TS

Fig. 1. Chemical structures of osthol

2:12 h light–dark cycle). They had free access to food and water adibitum. All animals were fasted overnight before the experiments.nimal welfare and experimental procedures were strictly in accor-ance with the guide for the care and use of laboratory animals andhe related ethical regulations of Nanjing Medical University.

.5.2. Drug administrationThe animals were randomly divided into four groups (n = 6). The

rst group, serving as control group, received an oral administra-ion of 20 mg/kg of Ost coarse powder suspended in 0.5% CMC-Na.ats in other three groups were orally administered with Ost-lasdone S-630, Ost-HPMC, Ost-Eudragit EPO solid dispersions athe same dosage of Ost separately. Blood samples (250 �l) wereollected into heparinized tubes from the suborbital vein at theredetermined time points of 0, 5, 10, 20, 30, 45 min, 1, 1.5, 2, 4,, 8, 12 and 24 h. Plasma samples were obtained by centrifuga-ion (3500 rpm, 10 min) and stored at −20 ◦C until analysis by anC–MS/MS method established in our previous report (Yun et al.,013).

Pharmacokinetic parameters were calculated by non-ompartment model using DAS 2.1.1 analysis software. Statisticalata analysis were performed using one-way ANOVA with p < 0.05s the criterion of significance.

. Results and discussion

.1. Solubility parameters

Similarity in the partial solubility parameters (ı) of the drug withhe polymers was used initially to screen the polymers to be used asarriers in the solid dispersion. The calculated solubility parameteror Ost is 23.31 MPa1/2 and values for the polymers (Chokshi et al.,005; Djuris et al., 2013; Forster et al., 2001; Sathigari et al., 2012)nd comparison of the differences (�ı) between ı of the drugs andhe polymers are shown in Table 1. Compounds with similar val-

es for solubility parameters are likely to be miscible, due to thenergy of mixing within the components is balanced by the energyeleased by interaction between the components (Greenhalgh et al.,999). Generally, the drug-excipient blends with difference in their

able 1olubility parameters for Ost and the polymers.

Drug/polymers Solubility parameter(ı) in MPa1/2

�ı Group classification

Ost 23.31 –Plasdone S-630 22.94 0.37 MiscibleHPMC-E5 22.4 0.91 MiscibleEPO 20.55 2.76 MiscibleSoluplus 19.15 4.16 MiscibleLactose 35.70 12.39 ImmiscibleGlucose 38.90 12.59 Immiscible

imperatorin (internal standard) (B).

solubility parameters (�ı) of <7.0 MPa1/2 are likely to be misciblewhereas those with �ı of >10.0 MPa1/2 are likely to be immiscible(Forster et al., 2001). Following these guidelines, since the valuesfor ı of Ost is calculated to be 23.31 MPa1/2, it can be predicted thatpolymer with a ı of 17–30 MPa1/2 should show some miscibilitywith the drug, whereas an excipient with a ı less than 17 or greaterthan 30 MPa1/2 is likely to be immiscible.

Therefore, based on the �ı summarized in Table 1, Plasdone S-630, HPMC, Eudragit EPO and Soluplus with a �ı of <7.0 MPa1/2

are likely to be miscible and form glass solutions when meltextruded with the drug. Whereas lactose and glucose with a �ıof >10.0 MPa1/2 are likely to be immiscible and are not expected toform a glass solution. Thus, Plasdone S-630, HPMC, Eudragit EPOand Soluplus were selected with the drug in the HME formulations.

3.2. Physicochemical characterization of solid dispersions

3.2.1. Drug contentAs determined by HPLC analysis, it was observed that the poly-

mers and drug were stable at the extrusion temperatures fordifferent polymers in processing the samples. And the drug contentin the prepared solid dispersions was at 97–103% of the theoreticalvalues.

3.2.2. DSC analysisDSC was used to identify the solid state of drug within the

extruded formulations and compared with that of the physical mix-tures. The DSC of Ost alone (Fig. 2) showed a single, sharp meltingendotherm at 86.5 ◦C, corresponding to the melting point of thecrystalline form of Ost. The physical mixture of Ost and PlasdoneS-630 showed an endotherm at 83.7 ◦C, with decreased intensity,whereas the melt extrudate had no distinct melting endothermfor the drug. The disappearance of endothermic peak indicatedthat Ost existed as amorphous state in the Plasdone S-630 pre-pared solid dispersions. Physical mixture of Ost with HPMC showedan endotherm at 84.4 ◦C, while with Eudragit EPO showed anendotherm at 84.6 ◦C, a little lower than the crystal drug. Hot meltextrudates of Ost with these two polymers showed that at thedrug/polymer ratio of 1:3 and 1:6, the characteristic features ofOst peak was visible (Fig. 2), with decreased peak intensity. Withthe increase of polymer ratio, the distinct peak of the drug wascompletely disappeared at the ratios of 1:9. Similarly, the physicalmixture of Ost and Soluplus showed endotherm at 83.8 ◦C, how-ever, the characteristic features of Ost peak gradually disappearedin the melt extrudates with the increase of polymer ratio. In general,thermal analysis supported the predictions from solubility param-eter calculations. The selected polymers would be miscible with the

drug in the HME formulations, but due to the solubility parameterof polymers, the mass ratio of drug and polymer presented differ-ence. Compounds with similar values of solubility parameter arelikely to be miscible (Djuris et al., 2013).

F. Yun et al. / International Journal of Pharmaceutics 465 (2014) 436–443 439

F S-630(

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ig. 2. Differential scanning calorimetry thermographs of (a) Osthole, (b) Plastone1:3), (e) solid dispersion (1:6), and (f) solid dispersion (1:9).

.2.3. XRPD analysisXRPD was used to confirm the disappearance of drug crys-

als, and the results of XRPD in different polymer systems werehown in Fig. 3. The pure Ost exhibited sharp distinct multipleeaks at 9.20◦, 10.94◦, 12.50◦, 17.34◦, 19.88◦, 21.00◦, 21.48◦, 26.10◦

nd 33.20◦ 2� angles within 60◦, indicating the crystalline naturef the drug. The binary physical mixtures of different polymersith the drug all presented several distinct peaks similar to crys-

alline Ost, suggesting that the drug still retains its crystallinity. Inhe case of the Plasdone S-630 prepared solid dispersions at all threerug/polymer ratios, no detectable diffraction peaks of Ost werebserved, indicating the presence of Ost in an amorphous state.or the HPMC prepared solid dispersions at the drug/polymer ratiof 1:3 and 1:6, just one distinct peak of Ost at 26.10◦ 2� exhib-ted in a very low intensity, and completely disappeared at therug/polymer ratio of 1:9, suggesting that Ost has been convertedo the amorphous form in HME prepared solid dispersion at suchrug/polymer ratio. The diffraction patterns of the Eudragit EPOnd Soluplus prepared Ost solid dispersions at the drug/polymeratio of 1:3 exhibited several distinct crystalline peaks similar torystalline Ost. With the increase ratio of Eudragit EPO and Solu-lus, the crystalline intensity of Ost was significantly reduced. Inummary, the results of XRPD and DSC indicated that Ost existed inn amorphous state after preparation of solid dispersion at appro-riate drug/polymer ratios.

.2.4. FTIR analysisInfrared spectroscopy has been widely used to investigate possi-

le drug–polymer interactions in solid dispersion systems. In ordero evaluate any possible solid–solid interactions between the drugnd carriers, FTIR spectra of Ost, physical mixtures, and HME for-ulations were recorded in Fig. 4. The IR spectra obtained for Ost

resented characteristic peaks C O stretch at 1722 cm−1, aliphaticH stretch in the range of 2840–3000 cm−1, aromatic C H stretch

n the range of 3000–3100 cm−1, and aromatic C C stretch at604 cm−1 and 1498 cm−1. Plasdone S-630 spectra showed C O at737 cm−1 and 1664 cm−1. FTIR spectra of Ost and Plasdone S-630hysical mixture presented as the result of combination of Ost andlasdone S-630 individual spectra. Plasdone S-630 has two groups

N and C O) that can potentially form hydrogen bonds with Ost

n the HME formulations. For the HME formulation at the drug-olymer ratio 1:6 and 1:9, the peak of C O stretch of the drug at722 cm−1 was absent, just leaving the C O at 1737 cm−1 of the

, HPMC, Eudragit EPO, or Soluplus, (c) physical mixture (1:6), (d) solid dispersion

polymer, which indicating physical interactions of Ost with Plas-done S-630.

FTIR spectra of HPMC exhibited characteristic peaks at3473 cm−1 (O H stretching), 2838–2940 cm−1 (C H stretching),and 1050–1150 cm−1 (C O stretching). In Fig. 4, FTIR spectra ofOst–HPMC physical mixture appeared as the result of summary ofOst and HPMC individual spectra, suggesting that no interactionoccurred between the drug and polymer in their physical mix-ture. However, the spectra of the HME extrudates showed a shift of1722.4 cm−1 (C O stretching) of the crystal drug to 1722.8 cm−1,1723.7 cm−1, and 1730 cm−1 in HME extrudates at the ratio of 1:3,1:6, 1:9, respectively. The 1252.1 cm−1 and 1280.4 cm−1 of C Ostretching shifted to higher frequency in HME extrudates. All theother peaks were smoothened, indicating physical interactions ofHPMC with Ost. Furthermore, the peak for OH group of HPMCat 3473 cm−1 (O H stretching) was shifted to lower frequency3458 cm−1 in HME extrudates due to intermolecular hydrogenbonding with Ost.

The Eudragit EPO exhibited C O stretch at 1730 cm−1, aliphaticC H stretch at in the range of 2770–2960 cm−1 and ester C Ostretch at 1150 cm−1, and Soluplus spectra showed C O stretch at1738 cm−1 and 1632 cm−1, and aliphatic C H stretch at 2932 cm−1.As shown in Fig. 4, both the spectra of physical mixtures and HMEformulations of these two polymers system are identical, and theOst skeleton stretching vibrations are not affected by the additionof polymers, suggesting no interaction occurs between the drug andthe polymer in their physical mixtures and HME formulations.

No additional peaks were observed in any of the all above binarysystems, indicating absence of any chemical interactions betweenOst and all the carriers.

3.2.5. In vitro dissolution studyDue to the extreme low solubility of the drug, 0.05% (v/v) Tween

80 was added to the dissolution medium to maintain sink condi-tions. Ost is a poorly soluble drug with a solubility of 2.3 �g/mL inwater. The saturation solubility of Ost achieved 15.26 �g/mL by theaddition of Tween 80 to the dissolution medium.

In our study, it was found that the solid dispersions dramat-ically improved the dissolution rate of Ost. As shown in Fig. 5A,

the dissolution of the HME formulation containing Plasdone S-630(D30 = 84%) at various drug/polymer ratios was approximately 3-fold higher than Ost alone (D30 = 28%) and 2-folder higher than thecorresponding physical mixture (D30 = 40%). The enhancement in

440 F. Yun et al. / International Journal of Pharmaceutics 465 (2014) 436–443

Fig. 3. X-ray powder diffraction plots of (a) Osthole, (b) Plastone S-630, HPMC, Eudragit EPO, or Soluplus, (c) physical mixture (1:6), (d) solid dispersion (1:3), (e) soliddispersion (1:6), and (f) solid dispersion (1:9).

Fig. 4. Fourier transform infrared spectra of (a) Osthole, (b) Plastone S-630, HPMC, Eudragit EPO, or Soluplus, (c) physical mixture (1:6), (d) solid dispersion (1:3), (e) soliddispersion (1:6), and (f) solid dispersion (1:9).

Fig. 5. Dissolution profiles of (A) Plastone S-630 systems, (B) HPMC systems, (C) Eudragit EPO systems, and (D) Soluplus systems.

F. Yun et al. / International Journal of Pharmaceutics 465 (2014) 436–443 441

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ig. 6. Mean plasma concentration–time profiles (±SD) after oral administrationC) Ost-Eudragit EPO solid dispersion (1:6), and (D) combination of osthole and diff

issolution in Plasdone S-630 extrudates is due to the conversionf crystalline drug into the amorphous state.

As shown in Fig. 5B, the dissolution the HPMC-based HME for-ulation (D30 = 77%, 81%, 83%) at various drug/polymer ratios was

pproximately 3-fold higher than Ost alone (D30 = 28%) or 2-foldigher than their corresponding physical mixtures (D30 = 30%, 35%,8%). The enhancement in dissolution in HPMC extrudates is proba-ly due to a decrease in the crystallinity of the Ost and the increasedettability.

For Eudragit EPO-based HME formulation (Fig. 5C), the D30 was3%, 81%, 84% for ratios of 1:3, 1:6, and 1:9, respectively. The 1:6nd 1:9 ratio of EPO-based HME extrudates improved the disso-ution rate of Ost by greater extent than 1:3 ratio extrudates. Thenhanced dissolution of 1:6 and 1:9 ratios of EPO-based HME extru-ates may be attributed to a decrease in the crystallinity of drug and

ts colloidal dispersion in the carrier. However, at the drug/polymeratio of 1:3, there was still some crystalline drug (confirmed by DSCig. 2 and XRPD Fig. 3 Eudragit EPO systems), which limited the drugissolution.

For Soluplus-based HME formulations (Fig. 5D), however, theissolution rate of the drug was not enhanced with this polymer.imilar dissolution results were reported for oxeglitazar extrusionystems with Soluplus (Kalivoda et al., 2012), due to a slow disso-ution rate of Soluplus.

The increase in the dissolution rate in the case of the HME for-ulation is attributed to the amorphous state of the drug that

ffers a lower thermodynamic barrier to dissolution. The physi-al mixture showed a little improved dissolution rate comparedith Ost but there was no statistical significance. The enhance-ent in dissolution rate for the physical mixture was probably due

) Ost-Plastone S-630 solid dispersion (1:6), (B) Ost-HPMC solid dispersion (1:6),solid dispersions (1:6).

to the hydrodynamic layer surrounding the drug particles in theearly stages of the dissolution process or to a local solubilizationaction existing in the microenvironment. The differences in the dis-solution profile among these HME extrudates were probably dueto the solubility/dissolution nature of the polymer. Other factorsthat might contribute to enhancement of the dissolution rate aregreater hydrophilicity, increased wettability and dispersibility, andreduction in the particle size of the drug. Dissolution of the drugin Plasdone S-630 and HPMC is governed by solubilization of thepolymer to create a hydrotropic environment for insoluble drug,whereas in the case of Eudragit EPO, the dissolution rate is pre-dominantly carrier controlled (Albers et al., 2009; Sathigari et al.,2012). It was observed in the dissolution studies that the PlasdoneS-630 and HPMC HME extrudates dissolved rapidly, whereas inthe case of physical mixture, Plasdone S-630 and HPMC dissolvedrapidly, leaving the crystalline drug in the dissolution medium. Thehigh dissolution rate of Ost from the Eudragit EPO at the 1:6 and1:9 ratios is possibly due to the drug–polymer microenvironment.Eudragit EPO has pH-dependent solubility and dissolves better inacid medium but less rapidly because the pH at the polymer sur-face is increased as some Eudragit EPO goes into solution, whichprevents the dissolution of the remaining undissolved polymer (Sixet al., 2004). The dissolution rate at the Ost/Eudragit EPO ratio of1:3 was lower than 1:6 and 1:9, which may due to crystalline drugcontained at the low drug/polymer ratio. In our practice, it waseasy to appear adhesion after pulverizing at the Ost/Eudragit EPO

ratio of 1:3, which may also retard its dissolution. For Soluplus HMEsystem without enhancing the dissolution rate of Ost, the main rea-son may be due to the lower solubility of Soluplus than other usedpolymers. In addition, it was noted that this drug carrier system

442 F. Yun et al. / International Journal of Pharmaceutics 465 (2014) 436–443

Table 2Mean pharmacokinetic parameters (±SD) after oral administration of Ost and HME extrudates of different polymers (n = 6).

Parameters Ost SD:Ost-PS630 SD:Ost-HPMC SD:Ost-EPO

Tmax (h) 1.65 ± 0.55 0.53 ± 0.25** 0.36 ± 0.07** 2.83 ± 1.81Cmax (ng/mL) 14.90 ± 3.28 68.05 ± 24.01** 86.88 ± 27.01** 21.06 ± 7.23AUC(0–24 h) (ng h/mL) 104.67 ± 24.37 147.84 ± 35.90* 147.40 ± 16.65* 111.88 ± 17.10AUC(0−∞) (ng h/mL) 109.85 ± 27.60 161.99 ± 64.24 148.45 ± 17.52* 113.94 ± 15.90MRT (h) 6.19 ± 0.26 4.52 ± 0.53** 3.88 ± 1.61* 6.52 ± 0.17T1/2 (h) 4.03 ± 1.43 3.76 ± 0.74 3.10 ± 1.36 3.90 ± 0.10CL (L/h/kg) 192.50 ± 52.33 136.29 ± 40.79 136.35 ± 16.54 178.19 ± 22.83

v

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s Ost group.* p < 0.05.

** p < 0.01.

oated on the dissolution medium for a long period during disso-ution experiments.

.3. In vivo pharmacokinetic study

Based on the results of in vitro dissolution test, HME formula-ion with Plasdone S-630, HPMC and Eudragit EPO at the ratio of:6 were chosen to further study the in vivo bioavailability study.ig. 6 showed the mean plasma concentration-time profile afterral administration of Ost alone and solid dispersions preparedith different polymers. The main pharmacokinetic parametersere summarized in Table 2.

The peak plasma concentration (Cmax) of Ost after oral admin-stration of pure drug, Ost-Plasdone S-630, Ost-HPMC, and Ost-udragit EPO solid dispersions were 14.90 ± 3.28, 68.05 ± 24.01,6.88 ± 27.01, and 21.06 ± 7.23 ng/mL, respectively, while theUC0–24 h were found to be 104.67 ± 24.37, 147.84 ± 35.90,47.40 ± 16.65 and 111.88 ± 17.10 ng h/mL, respectively. The phar-acokinetic profile and parameters clearly indicated that Cmax andUC of Ost could be significantly enhanced after preparation ofolid dispersions with Plasdone S-630 and HPMC, which may bettributed to the enhanced dissolution of these two polymers.

However, there was no improvement in the in vivo absorptionfter preparation of solid dispersion with Eudragit EPO. There coulde several reasons for this: One reason was that the solubility of thearrier Eudragit EPO was highly dependent on the pH of the dissolu-ion medium. The solubility of Eudragit EPO decreased quickly withn increase of pH, and may form gel matrix in intestinal environ-ent, which hence prevent the dissolution of Ost. Another reasonight be that when the solid dispersion reached the surface of

he gastrointestinal tract, the drug was immediately released form-ng an over-saturated solution above the absorption concentrationange of the body (Feng et al., 2012). Due to the potential gel for-ation of the polymer Eudragit EPO after entering into intestinalith high pH environment, the drug/polymer ratio equilibrium of

olid dispersion system would disrupt. The dissolved drug wouldrecipitated into low-soluble crystalline. Such process would hin-er the absorption of Ost because of the low solubility, thus leadingo the poor bioavailability.

The time taken to reach the Cmax was 1.65 h for the pure drug,owever, that was significantly decreased for Ost-HPMC solid dis-ersion (i.e. 0.36 h) and Ost-Plasdone S-630 solid dispersion (i.e.,.53 h). Cmax achieved by Ost-HPMC and Ost-Plasdone S-630 solidispersions were approximately 6-fold and 4.5-fold higher than theure Ost coarse powder, indicating better release from the solidispersion formulation. Moreover, the MRT(0−t) for Ost-Plasdone-630 and Ost-HPMC solid dispersions were notably decreased

han that of the pure drug powder. The increased Cmax and AUCuggested that the hot-melt extrusion technology prepared solidispersions was effective to enhance the bioavailability of pooroluble drug Ost.

4. Conclusions

As in this paper, based on solubility parameter calculation andthermal analysis, Plasdone S-630, HPMC, Eudragit EPO and Solupluswere used to prepare the solid dispersion. Although the crystallinedrug Ost was homogeneously dispersed in Plasdone S-630, HPMC,Eudragit EPO and Soluplus at appropriate ratio, however, the in vitrodissolution test showed that enhancement of Ost was obtainedonly by Plasdone S-630, HPMC and Eudragit EPO, while Soluplusexhibited no significant enhancement. The in vivo bioavailabilitystudy in rats showed that Plasdone S-630 and HPMC preparedsolid dispersions significantly increased the Cmax and AUC of Ostin comparison to that of pure Ost coarse powder, while no absorp-tion enhancement was observed in Eudragit EPO prepared soliddispersion. Therefore, Plasdone S-630 and HPMC are the optimalpolymers for Ost in the hot-melt extrusion process. Future researchwill have to be conducted to further investigate the stability of theextrudate.

As a summary, this study successfully demonstrated the appli-cation of hot-melt extrusion for the dissolution and bioavailabilityenhancement of the poor water soluble drug Ost with appropriatechoice of polymeric carriers. This study provides a great potentialto utilize oral solid dispersions as the effective formulation strat-egy for drugs with solubility/dissolution as the rate-limiting stepto absorption from the gastrointestinal tract.

Acknowledgments

This work was financially supported by the Priority AcademicProgram Development of Jiangsu Higher Education Institutions (No.2011ZYX3-001), Qing Lan Project of Jiangsu Province (No. 200806).

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