indomethacin-loaded methoxy poly(ethylene glycol)/poly(ε-caprolactone) diblock copolymeric...

*Corresponding author. Tel.: #82-2-2290-8269; fax: #82-2-2292-6686.E-mail address: [email protected] (J.S. Kang).

Biomaterials 22 (2001) 2049}2056

Indomethacin-loaded methoxy poly(ethylene glycol)/poly(�-caprolactone) diblock copolymeric nanosphere:

pharmacokinetic characteristics of indomethacinin the normal Sprague}Dawley rats

So Yeon Kim�, Young Moo Lee�, Hyun Jin Shin�, Ju Seop Kang��*�Department of Industrial Chemistry, College of Engineering, Hanyang University, Seoul 133-791, South Korea

�Department of Pharmacology, College of Medicine, Hanyang University, Seoul 133-791, South Korea

Received 27 April 2000; accepted 8 November 2000

Abstract

We prepared the drug-loaded polymeric nanospheres composed of the methoxy poly(ethylene glycol) (MePEG) and poly(�-caprolactone) (PCL) that showed a narrow size distribution and average diameter of less than 200 nm. We could obtain thenanosphere having a relatively high drug-loading e$ciency of about 42% when the feed weight ratio of indomethacin (IMC) topolymer was 1:1. To investigate the IMC pharmacokinetics in the IMC-loadedMePEG/PCL nanosphere (DMEP70) using the rats asanimal model, we analyzed the IMC concentration in plasma with HPLC after i.v. bolus administered at a dose of 10mg/kg in freeIMC (control) and IMC-loaded MePEG/PCL nanosphere (DMEP70) groups via tail vein. Pharmacokinetics parameters(mean$s.d.) such as the mean residence time (MRT, h), the steady-state volume of distribution (<

��, l), the terminal half-time (t

��, h)

and the plasma clearance (CL, l/h) of IMC in each groups (control vs. DMEP70) were determined; MRT (16.97$4.83 vs.28.69$11.28, p(0.01); <

��(14.26$4.86 vs. 20.37$12.04, p(0.05); t

��(15.12$4.77 vs. 23.1$8.24, p(0.01); CL (0.84$0.27

vs. 0.71$0.41). From these results, we could concluded that MEP70 has a signi"cant potential for sustained release and theenhancement of circulation time of loaded drug by prolonging terminal half-life, increasing MRT and <

��of IMC. Therefore, The

MePEG/PCL block copolymeric nanosphere system is being considered as promising biodegradable and biocompatible drug carriervehicles for parentral use and may be useful as sustained release injectable delivery systems for hydrophobic drugs. � 2001 ElsevierScience Ltd. All rights reserved.

Keywords: Methoxy poly(ethylene glycol); �-Caprolactone; Nanosphere; Drug delivery system; Pharmacokinetics

1. Introduction

There have been many studies to develop e$cientsystems for the site-speci"c delivery of drugs using appro-priate carrier systems [1}3]. Especially, a wide variety ofparticulate carriers has been devised for protecting theactive molecules against inactivation by the host and forcontrolling drug release in body #uids, e.g., blood, lymphand digestive juice [4}11]. Among them, new technologyfor the preparation of nano-sized biodegradable poly-meric particles has been required for providing a new

function to drug delivery systems [4,10,11]. Their ad-vantages are the easy control of particle size, good struc-tural stability, the solubilization of hydrophobic drugs,the stable storage and an ability to deliver drugs showinglow interactions with biocomponents such as proteinsand cells.

Generally, amphiphilic block or graft copolymerscomposed of hydrophilic and hydrophobic segments canform a micellar structure with a hydrophobic compactinner core and a hydrophilic swollen outer shell in a se-lective solvent, which is thermodynamically favorable forone block, but unfavorable for the others [12}22]. There-fore, the drugs with a hydrophobic character can beeasily incorporated into the core of nanosphere bya covalent or non-covalent bonding through hydrophobic

0142-9612/01/$ - see front matter � 2001 Elsevier Science Ltd. All rights reserved.PII: S 0 1 4 2 - 9 6 1 2 ( 0 0 ) 0 0 3 9 3 - 8

interactions in aqueous media. We have studied on theseveral nanospheres systems for an application as drugcarrier [23}28]. This is a continuing study on themethoxy (polyethylene glycol) (MePEG)/poly(�-cap-rolactone) (PCL) diblock copolymeric nanosphere re-ported previously [23,24]. To develop the degradablepolymeric nanospheres displaying the desired feature oflong-circulating carriers, we prepared amphiphilic dib-lock copolymeric nanospheres based onMePEG as a hy-drophilic group and PCL as a hydrophobic group. PCLis biocompatible, biodegradable material and also itsbiodegradability can be enhanced greatly by copolymer-ization. PEG has also nontoxic nature and is known toimpart a protein and cellular stealth properties to surfa-ces and interfaces. In our amphiphilic block copolymer,hydrophobic cores surrounded by water-soluble polargroups that extended into an aqueous medium and pro-duced a core-shell-type polymeric carrier. The coronaregion of nanosphere composed of PEG interacts withthe biological milieu. Therefore, it could achieve a longblood circulation half-life.

The aim of this study was to investigate the in#uence ofpolymeric nanosphere as drug delivery systems on phar-macokinetics of loaded drug using the rat as animalmodel. In this study, we prepared the MePEG/PCLblock copolymeric nanosphere (MEP70) containing in-domethacin (IMC) by dialysis method. Based on its char-acteristics such as particle size and drug-loadinge$ciency as a drug carrier, we designed this study toestimate the pharmacokinetics of IMC after intravenousbolus administration of IMC-loaded MePEG/PCLblock copolymeric nanosphere (DMEP70) in the normalSprague}Dawley rats.

2. Materials and methods

2.1. Chemicals

Methoxy poly(ethylene glycol) (MePEG, M�"

5.0�10� by supplier, M�"5.5�10� by our GPC

measurements) was supplied by Fluka and puri"ed byazeotropic distillation with benzene (Junsei Chemical Co.Ltd.). �-Caprolactone was purchased from Tokyo KaseiOrganic Chemicals and recrystallized from ethyl acetate.Indomethacin (IMC) and mefanamic acid (MA) was ob-tained from Sigma Chemical Co. (St. Louis, MO).Acetonitrile and all analytical reagents were HPLC-grade. Distilled}deionized water was prepared witha Milli-Q Plus System (Waters, Millipore, USA). Allother chemicals used were reagent grade and used aspurchased without further puri"cation. The stock solu-tions of both IDM and MA were prepared at concentra-tions of 2.0 and 0.2�g/ml in acetonitrile for in vivoexperiment, respectively. These solutions were stable at43C for at least 6 months.

2.2. Preparation of drug-loaded MePEG/PCL nanosphere

According to the procedure previously used by ourgroup, amphiphilic block copolymers composed ofMePEG and �-caprolactone were synthesized by the ringopening polymerization of �-caprolactone in the presenceof MePEG homopolymer without any catalyst [23,24].MePEG/PCL block copolymeric nanosphere containingIMC, which had hydrophobic property, as a model drugwas prepared as follows. MePEG/PCL block copolymer(100mg) was dissolved in 10ml of DMF followed byadding IMC (weight ratios to polymer"1 : 1) and stirredat room temperature. To form IMC-loaded micellarnanosphere and remove free IMC, the solution was dialy-zed for 24 h against 3 l of ultrapure water using cellulosedialysis membranes (molecular weight cut o!: 6.0�10�&8.0�10� and 12.0�10�&14.0�10�, size: 21/35,Sigma, USA). The micellar solution was sonicated usinga Branson 2210 sonicator (Branson Ultrasonics Co.,USA), and then centrifuged (Jouan BP403, France) toremove unloaded IMC and aggregated particles. Thesupernatant of nanosphere solution that was obtained inthis process was frozen and lyophilized by a freeze dryersystem (Labconco, USA), to obtain dried nanosphereproducts.

2.3. Physicochemical characterization of MePEG/PCLblock copolymer [23}29]

The molecular weight and molecular weight distribu-tion of block copolymer were determined by gel per-meation chromatography (GPC) apparatus (Waters-510HPLCpump,Milford, USA). They were characterized byelution time relative to polystyrene monodisperse stan-dards from GPC apparatus with aMILLENIUM softwareprogram. Three ultrastyragel� tetrahydrofuran (THF)columns (300mm�7.8mm, I.D., HR-0.5, HR-4, HR-5,all by Waters, Milford, USA) and Waters R-410 di!eren-tial refractometric detector were used. The mobile phasewas THF with a #ow rate of 1ml/min. The injectionvolume was usually 100 �l of stock solutions (0.1}0.5w/v%). The calibration curve was prepared beforemeasurements by using standard polystyrene (molecularweight: 1.28�10�, 2.96�10�, 1.13�10�, 2.85�10� and6.50�10�, respectively, Shodex Standard SM-105,Showa Denko, Japan). In addition, the composition andthe number-average molecular weight of each copolymerin CDCl

�solution were determined by 500MHz

�H NMR (Bruker AMX-500).Average size and size distribution of nanospheres were

determined by a dynamic light scattering (DLS) spec-trometer (Model 95 ION Lager, Lexel Laser Inc., USA)at a wavelength of 514 nm at 203C. The intensity of thescattered light was detected with a photomultiplier(Brookhaven Instrumental Co. EMI9863) at a scatteringangle of 903. The signal from the photomultiplier was

2050 S.Y. Kim et al. / Biomaterials 22 (2001) 2049}2056

digitized via an ampli"er-discriminator and was fed intoa correlator (Brookhaven Instrumental Co. BI-9000AT).The digital photon correlator accumulated the time cor-relation function was "tted by the use of the method ofCONTIN programs of Provencher et al. [29]. To assurethe correct alignment, we measured polystyrene standardsample, provided by Duke Scienti"c Co. in various con-ditions. We varied the light intensity as 50, 100, and200mW, the pinhole size as 100 and 200�m, the durationtime as 5, 4, 3, 2, and 1min, and the analysis method withcumulant, exponential, and CONTIN methods.

The samples for DLS measurement were prepared bythe dilution of a nanosphere solution with distilled}de-ionized water "ltered through a syringe "lter. It must bediluted enough, so that the multiple scattering may notoccur, in which the beam scattered from one particle isscattered again by the other. From these measurements,we obtained the diameter and variance of nanospheres.Furthermore, we measured the size of MePEG/PCLnanosphere as a function of time to investigate the stabilityof the nanosphere under the condition of micellar solution.

The nanosphere solution produced by dialysis proced-ure was sonicated and centrifuged to remove an unboundIMC and aggregated IMC-loaded nanosphere, and thenlyophilized. The nanosphere which were obtained byfreeze drying, were disrupted by the addition of ethanoland THF (1 : 1, v/v), the amount of IMC entrapped wasdetermined by measuring the UV absorbance at 319 nmusing the UV}visible spectrophotometer (ShimadzuModel UV-2101 PC). The IMC amount entrapped intothe core of nanosphere was calculated from the weight ofinitial drug-loaded nanospheres and the amount of drugincorporated from the following equation:

Drug loading efficiency (DLE)

"

Mass of IMC in nanosphere

Mass of IMC-loaded nanosphere�100.

(1)

2.4. Pharmacokinetic study

2.4.1. AnimalsAnimals (male Sprague}Dawley rats, 200}250g,

Myungjin Co., Seoul) were in stainless-steel cages ina ventilated (10}15 times/h) room under conditions ofcontrolled temperature maintained at 20}233C and hu-midity of 50}70% during the investigation. The noiseand luminous intensity of the controlled room with a12-h light and 12-h dark (6 : 00}18 : 00) cycle were below60db and 200 lx during the experiment, respectively. Freeaccess to food and water was allowed. Under anesthesiawith urethane (0.7 g/kg, i.p.), polyethylene catheters(PE50; Clay Adams, USA) were inserted into right fem-oral vein for serial blood sampling. Free IMC (liometacininj�, Boryung Pharm Co., Korea) and IMC-loadednanosphere were intravenous bolus administered ata dose of 10mg/kg in control and nanosphere groups

(n"10) through tail vein as a 0.5ml of saline solutionafter slight sonication for 5min. Blood samples weretaken through the femoral catheter about 1ml at 30min,1, 2, 4, 7 h and cardiac sampling at 24 and 48 h periodafter recovery from anesthesia. Plasma was separatedfrom blood by centrifugation at 2500�g for 10min. Eachplasma samples was stored at !203C until the nextexperiment.

2.4.2. Analysis of IDM in plasmaDetection of total IDM in plasma was determined by

employing a modi"ed HPLC method of Niopas andMamzoridi [30] and Sato et al. [31]. Brie#y, a 50�l ofplasma was pipetted into 1.5ml-tapered polypropylenetube, and then 200�l of internal standard stock solutionwas added. After vortex mixing for 30 s, the tubes werecentrifuged at about 10,000�g at 43C for 2min. A 200 �laliquot of the supernatant was transferred into 10mlglass-stoppered centrifuge tube and evaporated to dry-ness under vacuum with a vortex evaporator system. Theresidue was dissolved in 60�l of the mobile phase anda 40 �l aliquot was analyzed. For the calculation ofunknown plasma samples, peak-area ratios for IMC rela-tive to the MA as internal standard were used. Calib-ration graphs were obtained by analyzing control plasmasamples spiked with various concentrations of IMC solu-tions (0.1, 0.2, 0.4, 0.8, 1.6 and 3.2�g/ml). The linearity ofthe method was studied for six di!erent concentrations ofIMC in spiked plasma samples. Stock solutions of bothIMC andMA were prepared at concentrations of 2.0 and0.2�g/ml in acetonitrile, respectively. HPLC analysis wasperformed using a high-performance liquid chromato-graphic (HPLC) system consisting of Waters 510 pump,a variable wavelength ultraviolet absorbance detector(Waters-486) and TMC temperature controller. The re-corder used was a data module (Waters-475) which wasused for peak-area integration and calculations. Analysiswas performed on a 5�m LiChrosorb RP-18 (250mm�4mm I.D.; Merck Co.) and operated at 503C. The mobilephase of 6mM phosphoric acid}acetonitrile (50 : 50, v/v)was pumped at a #ow rate of 1.5ml/min and the columne%uent was monitored at 205nm.

2.4.3. Pharmacokinetic analysisThe total plasma concentration of IDM was plotted

semi-logarithmically against the time period after the i.v.bolus administration. The time pro"les of the disappear-ance of the 10mg/kg IMC and IMC-loaded nanosphere(DLE"42%) doses from the plasma were kineticallyanalyzed, based on the two-compartment open modelusing the nonlinear least-squares method [32,33] andPerrier and Mayersohn's method [34]. The plasma con-centration data were "tted into the two-exponentialequation as follows [35]:

C(t)"A�e��#B�e�� (2)

S.Y. Kim et al. / Biomaterials 22 (2001) 2049}2056 2051

where C(t) is the drug concentration at time t, A andB are ordinate axis intercept, and � and � are the corre-sponding "rst-order disposition rate constants. The totalbody clearance (CL), the steady-state volume of distribu-tion (<

��) and the elimination half-life (t

��) of the

� phase were calculated with the following relationships,independently. The total area under the plasma concen-tration}time curve (AUC) may be determined from thetrapezoidal rule or, more conveniently, by realizing thatthe total area underlying each exponential term is thezero-time intercept divided by its corresponding ex-ponential coe$cient (A;C"A/�#B/�). At the zerotime the anticipated plasma concentration is, by refer-ence to Eq. (2), equal to the sum of the coe$cients,A#B.At that time the amount of drug in the body is the dosewhich is administered intravenously. The mean residencetime (MRT) is a useful parameter to describe the sojournof drug molecules in the body (MRT"<

��/CL). The

apparent volume of distribution under steady-stateplasma concentrations (<

��) is useful in relating amount

in body to plasma concentration (<��

"dose�(A��#B��)/(A�#B�)�). The plasma clearance (CL) isde"ned as the proportionality factor-relating rate of drugelimination to plasma drug concentrations (CL"k<"

dose/(A/�#B/�)"dose/A;C). Because the terminalhalf-life is the elimination half-life for most drugs, thehalf-life (t

��) was calculated from the terminal phase of

the elimination curves (t��

"ln 2/�).

2.4.4. Statistical analysisStudent's t-test was used to determine signi"cance. The

0.05 and 0.01 levels of probability were used as the levelof signi"cance [36].

3. Results and discussion

3.1. Characterization of MePEG/PCL nanospheres

TheMePEG/PCL block copolymer could be preparedby ring-opening polymerization mechanism of �-cap-rolactone in the presence of MePEG homopolymer with-out any catalysts. The structure of MePEG/PCL blockcopolymers synthesized was identi"ed by Fourier trans-form-infrared (FT-IR) spectroscopy, wide-angle X-raydi!raction (WAXD) pattern, gel permeation chromato-graphy (GPC) and �H-NMR measurement [23}29].Table 1 shows the composition and molecular weight ofMePEG/PCL block copolymer measured by GPC and�H NMR analysis. The size and size distribution of thenanospheres prepared were determined by means of dy-namic light-scattering method. Fig. 1 shows the typicalsize distribution of MePEG/PCL block copolymericnanosphere and the average size was smaller than 200 nmand the size distribution showed a narrow and monodis-perse pattern from the DLS measurements. After the

IMC loading in MePEG/PCL, their size somewhat in-creased and the size distribution of micelle was relativelyidentical to that before IMC loading, maintaining thenarrow distribution. As shown in Table 1, the size ofMePEG/PCL nanospheres increased with the molecularweight of block copolymers. In addition, we estimatedthe stability of MePEG/PCL nanosphere by measuringthe change in size under the condition of micellar solu-tion. Fig. 2 exhibited the average size of MePEG/PCLnanosphere (MEP70, in Table 1) and IMC-loadedMePEG/PCL nanosphere (DMEP70, in Table 2) asa function of time. As seen in Fig. 2, the size of DMEP70was larger than that of MEP70. However, bothMePEG/PCL nanospheres did not show the signi"cantincrease in their size during 7 days and rather maintainedthe size of less than 200nm. Table 2 shows the amount ofIMC introduced into the block copolymer by controllingthe weight ratio between polymer and drug. Also, thedrug loading e$ciencies according to the molecularweights of MePEG/PCL block copolymer were de-scribed. As shown in this table, the drug loading e$cien-cy increased with the feed ratio of drug to polymer.However, in the preparation of nanospheres, the ag-gregation was found as we increased the polymer to anIMC ratio exceeding 1 : 1 because IMC had a hydropho-bic character. Therefore, the weight ratio of polymer toIMC was "xed to less than 1 : 1 in the drug loadingexperiment. In addition, as the molecular weights andhydrophobic chain lengths of a block copolymer in-creased, their drug-loading e$ciency gradually increased.

3.2. Pharmacokinetic analysis of IMC-loadedMePEG/PCL block copolymeric nanosphere

The typical chromatogram obtained from the ratplasma samples after the administration of IMC wasdepicted in Fig. 3. The retention times for IMC and MAwere 6.44 and 10min, respectively. The concentration oftotal plasma IMC was quanti"ed by the peak-areamethod withMA as an internal standard. The linearity ofregression line obtained from the calibration graph byanalyzing the control plasma spiked with variousamounts of IMC solution was determined in the concen-tration range from 0.1 to 3.2�g/ml. For IMC, the regres-sion lines were linear (y (con)"0.214�(ratio)!0.026,r"0.998). The mean plasma concentration}time pro"lesof IMC following intravenous bolus administration toSprague}Dawley rats in two di!erent formulations suchas free IMC and IMC-loaded nanosphere (DMEP-70)are shown in Fig. 4. Because the amount of IMC entrap-ped into the core of nanosphere is called was DLE of theDMEP-70 are about 42%, the actual amount of IMCthat was administered for the DMEP-70 group is about4.2mg/kg. But, the pharmacokinetic parameters of IMCsolution such as clearance, steady-state volume of distri-bution and terminal half-life were almost the same


Table 1Compositions and molecular weight distribution of MePEG/PCL diblock copolymers

Sample Feed molarratio�

Molarcomposition�

Composition(wt%)�

Composition(wt%)�

Number-averagemolecular weight

Polydispersity(MM

�/MM

�)

Particle sizemean$s.d. (nm)

�-CL/MePEG �-CL/MePEG MePEG: �-CL MePEG: �-CL Calc.� Expt'l.� Expt'l.�

MePEG 0 0 100 : 0 100 : 0 5000 5541 5333 1.128MEP35 35 21.8 68.9 : 31.1 66.9 : 33.1 8995 8037 7971 1.256 54$0.082MEP50 50 40.1 54.8 : 45.2 51.7 : 48.3 10,707 10,116 10,317 1.250 77$0.010MEP70 70 54.2 47.2 : 52.8 39.9 : 60.1 12,990 11,734 13,367 1.102 114$0.089MEP100 100 81.5 37.3 : 62.7 37.1 : 62.9 16,414 14,839 14,401 1.102 130$0.105MEP150 150 109.9 30.6 : 69.4 29.3 : 70.7 22,121 18,085 18,205 1.178 N.D.

�Determined on the basis of MM�of MePEG calculated in GPC experiments.

�Estimated as the di!erence between the experimental total MM�of copolymer and MePEG homopolymer in GPC experiments.

�Determined by �H NMR spectroscopy (CDCl�).

�Calculated from MePEG (M�

"5000, Fluka).�Measured by GPC analysis.

Fig. 1. Typical size distribution pro"le of MePEG/PCL diblockcopolymeric nanospheres (MEP-70) measured by dynamic light scat-tering method: (a) before loading IMC, (b) after loading IMC.

Fig. 2. Size change of IMC-loaded MePEG/PCL diblock copolymericnanospheres (DMEP-70) and unloaded nanosphere as a function oftime.

among the various dose levels [32]. The decay curve ofthe plasma concentration consisting of early rapid distri-bution phase and a slower elimination phase that istypical of many drugs was analyzed according to thetwo-compartment open model for each formulation us-ing nonlinear least-squares method [34]. The values ofestimated pharmacokinetic parameters of IMC in thecontrol and DMEP-70 group were listed in Table 3. Thebiexponential equation of control group isC(t)"0.63e��#0.38e�� and that of DMEP-70group is C(t)"0.19e��#0.12e��, where t is timein hours, adequately describes the decline in plasma IMCconcentration following the 10 and 4.2mg bolus actualdose. At time zero the anticipated plasma concentration(C

�) is equal to the sum of the initial and terminal

coe$cients, A#B by reference to Eq. (2). The meanC

�and AUC of the DMEP-70 group that treated with

42% of control group is 0.3$0.12 and 5.29$2.82 thatare about 30 and 44% of that of control group, respec-tively. The mean ($s.d.) values of various phar-

macokinetic parameters such as <��

(20.37$12.04),MRT (28.69$11.28), and terminal half-life (23.1$8.24)in the DMEP-70 group were signi"cantly di!erent from14.26$4.86, 16.97$4.83, and 15.12$4.77 in the con-trol group, respectively. But, total plasma clearance (CL)of DMEP-70 group was slightly di!erent and not statis-tically important from control group. Since the totalplasma clearance (CL) was not signi"cantly changed be-tween two groups, we could conclude that our carriersystem did not a!ect the rate of IMC elimination. Afterintravenous bolus injection of IMC-loaded nanosphere,mean<

��, MRT, and terminal half-life were signi"cantly

increased than that obtained with injection of IMC solu-tion. These results were suggested that the extravasculardistribution of IMC-loaded nanosphere be increased ascompared to IMC solution. This phenomena have been


Table 2Indomethacin loading contents of MePEG/PCL block copolymericnanosphere

No. Sample MePEG/PCLcopolymer used

Feed weight ratio Drug loadingcontent

IMC� Polymer (DLE) (%)�

1 DIP25 MEP70 0.25 1.0 16.332 DIP50 MEP70 0.50 1.0 20.993 DIP75 MEP70 0.75 1.0 31.964 DIP100 MEP70 1.00 1.0 41.985 DMEP35 MEP35 1.00 1.0 25.836 DMEP50 MEP50 1.00 1.0 34.087 DMEP70 MEP70 1.00 1.0 41.988 DMEP100 MEP100 1.00 1.0 42.03

�Indomethacin.

�DLE (%)"amount of indomethacin in nanospheres

amount of indomethacin loaded in nanospheres�100

"

IMC

IMC#polymer�100.

Fig. 3. Typical high-performance liquid chromatogram of the plasmaindomethacin. Peaks: (a) indomethcin (IMC); (b) mefenamic acid (inter-nal standard).

Fig. 4. Plasma concentration time pro"les of indomethacin (IMC,�g/ml) after i.v. bolus administration at a dose of 10mg/kg of free IMC(control) and IMC-loaded nanosphere (DMEP-70) with DLE of41.98% for 48h in the normal Sprague}Dawley rats. Each point repres-ents the mean$s.d. (n"10).

Table 3Pharmacokinetic parameters of indomethacin after intravenous bolusadministration at a dose of 10mg/kg in free indomethacin (control-)and indomethacin-loaded MePEG/PCL nanosphere (DMEP70-)group in the normal Sprague}Dawley rats

Pharmacokineticparameter�

Control� p-value( DMEP70�

Initial plasmaconcentration(Co, �g/ml)

1.04$0.24 0.30$0.12

Area under curve(AUC, �g h/ml)

11.90$3.70 5.95$2.82

Mean residencetime (MRT, h)

16.97$4.83 0.01 28.69$11.28

Steady-state volume ofdistribution (<

��, l)

14.26$4.86 0.05 20.37$12.04

Terminal half-time(t��

, h)15.12$4.77 0.01 23.1$8.24

Plasma clearance(CL , l/h)

0.84$0.35 NS� 0.71$0.41

�All values represent mean$s.d. (n"10). p-value indicated the com-parison of values of each groups obtained (Student's t-test).�Control-group; single administration of free IMC.�DMEP70-group; single administration of IMC-loadedMePEG/PCL

nanospheres with DLE of 41.98%.�NS: not signi"cant.

described by Fawaz et al. [37] in the IMC-loadedpoly(D,L-lactide) nanocapsules experiment.

4. Conclusions

We prepared the MePEG/PCL copolymeric nano-sphere entrapped with hydrophobic drug IMC in their

inner core by the solution behavior of block copolymer inselective solvents. The size of IMC-loaded MePEG/PCLnanosphere was less than 200nm and its size distributionexhibited the narrow pattern. Furthermore, we couldobtain the MePEG/PCL nanospheres having relativelyhigh DLE of more than about 40% when the feed weightratio of IMC to polymer was 1 : 1. The size of MePEG/


PCL nanosphere did not considerably increase andmaintained the size of less than 200 nm during 7 daysunder the condition of micellar solution. We demon-strated in normal Sprague}Dawley rats that severalpharmacokinetic parameters of the IMC such as <

��,

MRT and terminal half-life in the IMC-loaded nano-sphere DMEP70 group showed signi"cant changes fromthe free IMC control group. As a consequence, theseresults show that the e!ects of MePEG/PCL nanosphereas drug delivery system on pharmacokinetics of loadeddrugs was signi"cant that it was prolong retention timeand terminal half-life and increase volume of distributionin vivo experiment. From these results, we could con-cluded that the MePEG/PCL block copolymeric nano-sphere system has a signi"cant potential for sustainedrelease and the enhancement of circulation time of loadeddrug by prolonging terminal half-life, increasing MRTand <

��of IMC. Therefore, this MePEG/PCL block

copolymeric nanosphere is being considered as promis-ing biodegradable and biocompatible drug vehicle ap-proach for parentral administration and may be useful assustained release injectable delivery systems for hydro-phobic drugs to a speci"c organ or target sites.

Acknowledgements

The Korea Research Foundation supported this re-search in the year 1998. SYK is grateful to the GraduateSchool of Advanced Materials and Chemical Engineer-ing at Hanyang University for a fellowship.

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