Improved solubility of docetaxel using a

Docetaxel microemulsion/Asian Journal of Pharmaceutical Sciences 2009, 4 (6): 331-339

Improved solubility of docetaxel using a microemulsion delivery system: formulation optimization and evaluation Yongmei Yina, b, Fude Cuia, Chaofeng Mua, b, Suk-Jae Chungb, Chang-Koo Shimb, c, Dae-Duk Kimb, * a

School of Pharmacy, Shenyang Pharmaceutical University, Shenyang 110016, China College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, South Korea c National Research Laboratory for Transporters Targeted Drug Design, Seoul National University, South Korea

b

Received 26 March 2009; Revised 15 June 2009; Accepted 19 November 2009

_____________________________________________________________________________________________________________

Abstract Purpose: To optimize microemulsion formulations for improving the solubility of docetaxel and systematically evaluate them in vitro and in vivo. Methods: Pseudo-ternary phase diagrams were constructed to optimize the composition of the microemulsion systems. The droplet size of microemulsions was determined by an electrophoretic light-scattering spectrophotometer while the appearance was visually examined. The in vitro cytotoxicity of docetaxel-loaded microemulsions and commercial formulation (Taxotere®) against three breast cancer cell-lines was determined by the MTT dye reduction assay. Finally, the pharmacokinetics of docetaxel microemulsions was studied in SD rats and compared with that of Taxotere®. Results: Using the microemulsion systems selected from the pseudoternary phase diagrams, the maximal solubility of docetaxel was as high as 30 mg/ml which was a significant increase compared with its aqueous solubility. The droplet size of the microemulsions was around 30 nm with a narrow distribution. The in vitro cytotoxicity of three microemulsions against three cancer cell-lines was not significantly different from that of Taxotere®. Additionally, animal studies showed that the docetaxel-loaded microemulsion (Capryol 90/Cremophor RH 40/Transcutol/water) produced a significantly higher area under the curve (AUC) (1689.4 v.s. 905.23 h·ng/ml) and a longer t1/2β (3.49 v.s. 1.64 h) compared with Taxotere®. Conclusion: The solubility of docetaxel could be successfully improved by microemulsion systems and these appear to be a promising alternative carrier for intravenous delivery of docetaxel. Keywords: Docetaxel; Microemulsion; Solubility _____________________________________________________________________________________________________________

Thus, its commercial formulations (Taxotere®) are available as single-dose vials of concentrated anhydrous docetaxel in polysorbate 80 [2]. Intraveous injection of Tween 80 can cause some toxic effects including fluid retention and hypersensitivity reactions [6, 7]. In addition, because of the limited solubility of Tween 80, precipitate or particulate matter may appear after Taxotere® is diluted for clinical usage. Microemulsions are clear, stable, isotropic liquid mixtures of oil, water and surfactant, frequently used in combination with a co-surfactant. They offer considerable promise as means of increasing the aqueous solubility of poorly water-soluble drugs to the extent (103- to 105-fold) necessary for the relatively high concentrations (1–100 mg/ml), which are frequently required in parenteral use [8]. Several sparingly soluble lipophilic drugs have been formulated as O/W microemulsions for parenteral delivery [9-11]. Due to their biocompatibility and the long-term stability, microemulsions with an

1. Introduction Docetaxel is a clinically well established anti-mitotic form of chemotherapy used mainly for the treatment of breast, ovarian and non-small cell lung cancer [1, 2]. It is a semi-synthetic analogue of paclitaxel, and extracted from the rare pacific yew tree Taxus brevifolia [2]. It has significantly higher cytotoxic activity than paclitaxel against human ovarian, endometrial, colon and breast cancer cell lines [3, 4]. Moreover, other studies have been carried out on its antitumor effect in small-cell lung cancer, melanoma and soft-tissue sarcomas [5]. Unfortunately, however, docetaxel is a highly lipophilic white powder and practically insoluble in water. __________ *Corresponding author. Address: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul 151-742, South Korea. Tel.: +82-2-8807870; Fax:  +82-2-8739177 E-mail: [email protected]

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internal phase diameter in the submicron region can be used for intravenous administration [12]. In the present work, our aim was to prepare microemulsions of docetaxel in order to improve its poor water solubility. By constructing pseudo-ternary phase diagrams, the composition of the microemulsions was optimized, and the in vitro characterization, cytotoxicity and in vivo pharmacokinetics were studied to evaluate the performance compared with Taxotere®.

were cultured in DMEM supplemented with 10% heat inactivated FBS and a 1% antibiotic solution (100 U/ml penicillin G and 0.1 mg/ml streptomycin). Cells were maintained at 37˚C in a humidified incubator containing 5% CO2. 2.3. Construction of a pseudo-ternary phase diagram and preparation of microemulsions The titration method was used to construct the pseudo-ternary phase diagrams. Briefly, mixtures of oil and surfactant/co-surfactant in selected weight ratios were diluted dropwise with water. In this study, Capryol 90 was selected as the oil phase based on a preliminary solubility study. The ratio of surfactant to co-surfactant (Km values) was set at 4: 3, 3: 2 and 2: 1 (w/w), respectively, and the resultant surfactant mixture (Sm) was vortexed for 30 sec. Then, the mixture of the oil phase and Sm was titrated with water and its phase clarity and flow ability were examined visually. By constructing pseudoternary phase diagrams and locating the microemulsion region, microemulsion systems with a broad O/W microemulsion range were selected from the phase diagrams. In order to optimize the composition of the docetaxel microemulsion, the formulations were prepared using several ratios of oil to Sm (4.1: 5.9; 4.4: 5.6; 4.7: 5.3) over the microemulsion area. The formulations were optimized by droplet size and viscosity. Then, the components and composition of the optimized formulations were obtained. Using the optimized components and proportions of oil, Sm and water, fine microemulsions could be formed spontaneously by gentle agitation. Docetaxel was added to the oil phase prior to preparing the microemulsions as mentioned above and drug-loaded microemulsions were formed.

2. Materials and methods 2.1. Materials Docetaxel was obtained from Taihua Co. (Xi’an, China) while Capryol 90 was a gift from Gattefossé Co. (Saint Priest, France). Tween 80 was bought from Kanto Chemical Co. Inc (Tokyo, Japan) and Transcutol was obtained from Sigma-Aldrich (St. Louis, USA). Cremophor EL, and Cremophor RH40 were both pur-chased from BASF Co. (Ludwigshafen, Germany). Propylene glycol (PG) and PEG400 were from Duksan Pure Chemical Co. Ltd. (Ansan, Korea) and 3-(4, 5-Dimethyltiazol-2-ly)-2, 5-diphenyltetrazolium bromide (MTT) was obtained from Sigma Chemical Co. (St. Louis, MO, USA). Dulbecco’s modified Eagle’s medium (DMEM), MEM, nonessential amino acid solution and, penicillin-streptomycin, and fetal bovine serum were obtained from Sigma-Aldrich (St. Louis, USA) and Invitrogen (Ontario, Canada), respectively. Acetonitrile and methanol were HPLC grade and supplied by Fisher Scientific Korea Ltd. (Seoul, Korea). All other chemicals were of analytical grade or higher. 2.2. Cell culture SK-BR-3, MCF-7 and MDA-MB-231 human breast cancer cell lines were obtained from the American Type Culture Collection (Rockville, MD, USA). SK-BR-3 and MCF-7 cells were cultured in MEM supplemented with 10% heat-inactivated fetal bovine serum (FBS) and a 1% antibiotic solution (100 U/ml penicillin G and 0.1 mg/ml streptomycin). MDA-MB-231 human breast cancer cells

2.4. Mean droplet size and distribution An electrophoretic light-scattering spectrophotometer (ELS-8000, Otsuka Electronics Co. Ltd., Japan) was used to determine the droplet size and distribution of the microemulsions. The microemulsions were transferred

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to a standard quartz cuvette, and the droplet size and polydispersity index of the microemulsions were determined using dynamic He–Ne laser (10 mW) light scattering at an angle of 90˚ at 25˚C. Data were analyzed using a software package (ELS-8000 software) supplied by the manufacturer. In addition, the appearance of the microemulsions was examined visually.

docetaxel were obtained from the concentration-effect curves, taking the optical density of the control well as 100%. 2.7. Pharmacokinetics studies The pharmacokinetic study was performed using male Sprague-Dawley rats (250–270 g, Dae-Han Biolink, Daejeon, Korea). The experimental protocols involving the animal study were approved by the Animal Care and Use Committee of the College of Pharmacy, Seoul National University, according to the National Institutes of Health Guidelines (NIH publication #85-23, revised in 1985). The rats were fasted overnight with access to water ad libitum before the experiment and randomly divided into 4 groups (n = 4) Under anesthesia, with the animals in the supine position, the femoral arteries and veins were cannulated with polyethylene tubing (PE-50, Clay Adams, Parsippany, NJ, USA) containing 50 IU/ml heparin in saline. When rats had completely recovered from the anesthesia, each single diluted formulation (Taxotere® or microemulsions with a docetaxel concentration of 1 mg/ml) was administered via the femoral vein at a docetaxel dose of 8 mg/kg. Blood samples were withdrawn from the femoral artery at predetermined time intervals for 6 h. After centrifuging at 7000 × g for 5 min, 100 μl plasma samples were obtained and stored at −20˚C until analysis. The concentration of docetaxel in plasma was determined by the method of Ciccolini using liquidliquid extraction with minor modifications [14]. The HPLC system was equipped with a Waters 2487 Dual λ Absorbance Detector, a 717 plus Autosampler and 515 HPLC dual pumps. A Capcell PAK C18 MG HPLC column (4.6 mm × 250 mm, 5 μm, Shiseido, Japan) was used at room temperature. The wavelength of the UV detector was set at 230 nm. For the blood samples, the mobile phase consisted of acetonitrile : acetate buffer (pH 5) : tetrahydrofuran (45: 50: 5, v/v) at the flow rate of 1.0 ml/min while a mixture of acetonitrile: water (65: 35, v/v) was used for in vitro samples at a flow rate of 1.0 ml/min. The plasma concentration profiles

2.5. Viscosity determination The viscosity of each formulation was measured using a DV-E viscometer (Brookfield Engineering Laboratories, Middleboro, MA, USA) at 25˚C in triplicate. The samples were contained in cylindrical bottles, 2.4 cm in diameter and 4.5 cm in height. The measurement was performed with a No. 16 spindle provided by the company and the shear rate was set at 100 r/min. 2.6. In vitro cytotoxicity study Three breast cancer cell lines (MDA-MB-231, SKBR-3 and MCF-7) were used to determine the cytotoxicity of the docetaxel-loaded microemulsion and Taxotere® by the MTT dye reduction assay [13]. Briefly, 1.0 × 104 cells/well during the exponential growth phase were plated in 96-well flat-bottom tissue-culture plates. The cells were incubated at 37˚C in a 5% CO2 incubator for 24 h, during which the cells became attached and resumed their growth. Microemulsions were diluted with the culture medium to obtain different concentrations of docetaxel, and these were added to each well (200 μl each). Control wells were treated with an equivalent volume of docetaxel-free medium. After 24 h, the supernatant was removed. MTT powder was dissolved in PBS (pH 7.4) at a concentration of 5 mg/ml and diluted 10-fold with culture medium. Then, 200 μl was added to each well and incubated for 4 h. The unreduced MTT and medium were discarded and then 200 μl DMSO was added to dissolve the MTT formazan crystals. Plates were shaken for 10 min and the absorbance was read at 560 nm using a microplate reader (Molecular Devices Corporation, USA). The IC50 values (i.e., concentration resulting in 50% growth inhibition) of

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of docetaxel were fitted to a conventional two-compartment model using the WinNonlin® program (Version 3.1, Pharsight Co., Mountainview, CA, USA).

increased with the reduction in the Transcutol content from the Km value of 4:3, 3:2 to 2:1. Fig. 2 shows the phase diagrams of the compositions of Cremophor EL with PG, PEG400 and ethanol with a Km value of 2:1. It appears that the combination of Cremophor EL and ethanol results in a greater O/W microemulsion area in the diagrams while the volatility of ethanol will limit the long stability of the microemulsion during clinical usage. In addition, the proportion of oil was lower in Fig. 2A than in Fig. 1C and Fig. 2B. Thus, ethanol was not a suitable component of the optimized formulation. From Fig. 1 and Fig. 2, the composition of Capryol 90/ Cremophor EL/Transcutol (Fig. 1C) and Capryol 90/ Cremophor EL/PG (Fig. 2B) formed a wide O/W microemulsion area compared with that of Fig. 2C and, thus, these two systems were selected to perform further studies for formulation optimization. When Cremophor RH40 was used as a surfactant, the O/W microemulsion area of its compositions with Transcutol, PG, PEG400 and ethanol was compared in Fig. 3 (Km value of 2: 1). As shown in the figure, the O/W microemulsion area of the composition of Capryol 90/Cremophor RH40/ Transcutol was the greatest compared with the other diagrams using Cremophor RH40 as surfactant. In the case of Tween 80 as the surfactant, the O/W microemulsion area was quite small as shown in Fig. 4 and the formulations with Tween 80 were not included in this study. Based on the above results, three O/W microemulsion systems which exhibited good O/W microemulsion formation capacity (Capryol 90/Cremophor EL/PG, Capryol 90/Cremophor RH40/Transcutol, and Capryol 90/Cremophor EL/Transcutol) were selected for further optimization. Three formulations of each of the above mentioned systems with a different ratio of oil to Sm are listed in Table 1 together with their droplet size and viscosity. As shown in Table 1, the droplet size of microemulsions slightly increased as the Sm content decreased. On the other hand, the viscosity of the microemulsions decreased along with a decrease in the amount of Sm in the microemulsions. In order to prepare microemulsions with a low droplet size as well as low viscosity and a minimum amount of surfactant, the ratio of oil to Sm was fixed at 4.4: 5.6 and these were named F1, F2 and F3.

2.8. Statistical analysis All the experiments in the study were performed at least three times and all the data were expressed as the mean ± standard deviation.

3. Results and discussion 3.1. Optimization of microemulsion formulations Although several microemulsion systems have been reported in the literature, the challenge for the pharmaceutical formulator is to predict which type of oil and surfactant should be selected for a particular application, because these differ markedly from case to case. For example, different oils have different requirements for the HLB value of surfactants and different model drugs may have particular effects on the phase behavior [15]. Therefore, a phase diagram study is extremely important and necessary for the preparation of microemulsions or other emulsion systems. In order to select other components (surfactant and co-surfactant) of the microemulsion system and optimize the proportion of each excipient, pseudo-ternary phase diagrams were constructed. Nonionic surfactants are preferred in pharmaceutical applications due to the poor stability and toxicological concerns associated with ionic surfactants. Several types of nonionic surfactants and alcohols can actas co-surfactants in a given microemulsion. A low HLB co-surfactant is usually matched with a high HLB surfactant [16]. Based on the above rationale, several pseudo-ternary phase diagrams were constructed in this study as shown in Fig. 1–4 and the gray area represents the O/W microemulsion range, the shadedarea represents the W/O microemulsion area and the “E” area is the crude emulsion range. Fig. 1 shows that when Cremophor EL and Transcutol were used as surfactant and co-surfactant, respectively, the O/W microemulsion area of this composition was the greatest while the ratio of Cremophor EL to Transcutol was 2:1. The O/W microemulsion area 1 334 1

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(C) (B) (A)

Fig. 1. Pseudo-ternary phase diagrams indicating the microemulsion region, where the ratio of Cremophor EL to Transcutol was (A) Km = 4: 3 (w/w), (B) Km = 3: 2 (w/w) and (C) Km = 2:1 (w/w). The gray area represents the O/W microemulsion range. The shaded area represents the W/O microemulsion area and the “E” area is the crude emulsion range.

(C) (B) (A)

Fig. 2. Pseudo-ternary phase diagrams indicating the microemulsion region, where Sm is composed of (A) Cremophor EL and EtOH, (B) Cremophor EL and PG, and (C) Cremophor EL and PEG400 with a Km of 2: 1 (w/w). The gray area represents the O/W microemulsion range. The shaded area represents the W/O microemulsion area and the “E” area is the crude emulsion range.

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(D) (C) (B) (A)

Fig. 3. Pseudo-ternary phase diagrams indicating the microemulsion region, where Sm is composed of (A) Cremophor RH 40 and Transcutol, (B) Cremophor RH 40 and EtOH, (C) Cremophor RH 40 and PG, and (D) Cremophor RH 40 and PEG400 with a Km of 2: 1 (w/w). The gray area represents the O/W microemulsion range. The shaded area represents the W/O microemulsion area and the “E” area is the crude emulsion range.

(D) (C) (B) (A)

Fig. 4. Pseudo-ternary phase diagrams indicating the microemulsion region, where Sm is composed of (A) Tween 80 and Transcutol, (B) Tween 80 and EtOH, (C) Tween 80 and PEG400, and (D) Tween 80 and PG with a Km of 2:1 (w/w). The gray area represents the O/W microemulsion range.

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3.2. Characterization of the microemulsions

in water). Accordingly, the final content of docetaxel in the microemulsions was set at 20 mg/ml for the subsequent studies.

The biopharmaceutical characteristics and preparation stability are directly related to the physical properties of microemulsions, including the microstructure, droplet size and location of the drug molecule in the microemulsion [16]. One example of the droplet size determination of the three microemulsions shows a monopeak and a low polydispersity index (Fig. 5). Fig. 6 shows the appearance of those microemulsions, which were clear and transparent. In addition, when the microemulsions were diluted with water (over a 10-fold dilution), the transparency did not change and a light sky-blue opalescence was observed. The solubility of docetaxel in those three microemulsions was increased to 20–30 mg/ml which was much greater than its solubility in aqueous solution (4.93 µg/ml (A)

(A)

F1

(B)

F2

(C)

F3

Fig. 6. Appearance of the resulting microemulsions: (A) F1, (B) F2 and (C) F3.

(B)

(C)

Fig. 5. Droplet size and polydispersity index of microemulsions: (A) F1, (B) F2 and (C) F3 determined by electrophoretic light-scattering spectrophotometry (ELS-8000). Table 1 Composition, droplet size and viscosity of microemulsions (mean ± SD, n = 3). Formulations

Surfactant/co-surfactant

Rx1 Rx2 (F1)

Cremophor EL/PG

Rx3 Rx4 Rx5 (F2) Rx6

Cremophor RH40/ Transcutol

Rx7 Rx8 (F3) Rx9

Cremophor EL/Transcutol

Ratio of oil to Sm

Droplet size (nm)

Viscosity (cP)

4.1: 5.9

30.8 ± 5.1

100 ± 2

4.4: 5.6

31.0 ± 3.7

98 ± 4

4.7: 5.3

37.2 ± 4.4

96 ± 3

4.1: 5.9

33.9 ± 6.1

77 ± 4

4.4: 5.6

34.7 ± 3.8

76 ± 3

4.7: 5.3

39.2 ± 4.8

73 ± 2

4.1: 5.9

30.7 ± 3.5

80 ± 3

4.4: 5.6

31.5 ± 2.1

79 ± 3

4.7: 5.3

35.2 ± 3.3

77 ± 2

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3.3. In vitro cytotoxicity study

pharmacokinetic parameters which were calculated based on the observed plasma levels of docetaxel are shown in Table 3, and plasma concentration-time profiles are shown in Fig. 7. The t1/2β of the microemulsions was relatively longer than that of Taxotere®, while their clearance values were lower than Taxotere®. This means that docetaxel in microemulsion formulations (especially F2) circulated in the bloodstream for a longer period than that of Taxotere®. Also, the AUC of the microemulsion formulations was also significantly higher compared with that of Taxotere®. The above results showed that the microemulsion formulations could prolong the time of action of docetaxel. This was possibly due to protection the microemulsion droplets from RES recognition and uptake [17]. However, the exact mechanism will remain unclear until further work is carried out. In conclusion, the pharmacokinetic parameters of docetaxel were altered in F1, F2 and F3 compared with that of Taxotere®. Docetxel in microemulsions had a prolonged half-life compared with Taxotere®, indicating potentially enhanced exposure of docetaxel to tumor sites. This may contribute to an improvement in the antitumor efficacy of docetaxel.

The cytotoxicity of docetaxel in three microemulsion formulations against three breast cancer cell lines was compared with that of Taxotere® by MTT assay. The IC50 values of the formulations are summarized in Table 2. The SK-BR-3 cell line was more sensitive to docetaxel and the IC50 values were less than 100 ng/ml while the MCF-7 cell line exhibited the highest IC50 values among the three tested cell lines. It also appeared that the cytotoxicity of docetaxel against the three breast cancer cell lines did not differ significantly between the microemulsions and Taxotere®. This also means that the encapsulation of docetaxel into the microemulsion formulations did not alter its in vitro cytotoxicity and the excipients of the microemulsion did not affect its antitumor activity. 3.4. Pharmacokinetic study The release of docetaxel from microemulsions was compared with that of Taxotere® after a single intravenous injection (8 mg/kg) to male Sprague-Dawley rats. The

Table 2 IC50 of Taxotere® and microemulsions loaded with docetaxel (ng/ml, mean ± SD, n = 6). Formulations

MDA-MB-231

SK-BR-3

MCF-7

Taxotere

157.36 ± 17.1

72.09 ± 6.2

309.66 ± 23.2

F1

141.15 ± 16.8

26.85 ± 8.7

426.86 ± 30.5

F2

110.63 ± 15.9

22.1 ± 9.3

442.64 ± 32.1

F3

176.16 ± 17.8

49.6 ± 7.7

534.18 ± 39.5

®

Table 3 Pharmacokinetic parameters of each formulation after intravenous injection to rats (mean ± SD, n = 4). Parameters

Taxotere®

F1

F2

F3

AUC (h·ng/ml)

905.23 ± 99.54

1283.52 ± 65.5

1689.4 ± 267.7

1449.80 ± 179.3

t1/2α (h)

0.072 ± 0.01

0.066 ± 0.003

0.074 ± 0.01

0.062 ± 0.002

t1/2β (h)

1.64 ± 0.29

1.79 ± 0.19

3.49 ± 1.4

2.43 ± 0.63

CL (l/h/kg)

9.39 ± 1.09

6.24 ± 0.31

4.81 ± 0.63

5.57 ± 0.69

MRT (h)

1.73 ± 0.28

1.74 ± 0.16

3.95 ± 1.8

2.38 ± 0.65

Vss (l/kg)

15.12 ± 5.54

10.86 ± 0.53

18.11 ± 0. 8

12.97 ± 0.22

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Plasma concentration of docetaxel (ng/ml)

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[2] S. J. Clarke, L. P. Rivory. Clinical pharmacokinetics of docetaxel. Clin Pharmacokinet., 1999, 36: 99-114. [3] M. C. Bissery. Preclinical pharmacology of docetaxel. Eur. J. Cancer, 1995, 31: S1-S6. [4] U. Vanhoefer, S. Cao, A. Harstrick, et al. Comparative antitumor efficacy of docetaxel and paclitaxel in nude mice bearing human tumor xenografts that over-express the multidrug resistance protein (MRP). Ann. Oncol., 1997, 8: 1221-1228. [5] A. M. Mac Connachie. Docetaxel (Taxotere, Rhone-Poulenc Rorer). Intensive Crit. Care Nurs., 1997, 13: 119-120. [6] E. K. Rowinsky. The development and clinical utility of the taxane class of antimicrotubule chemotherapy agents. Annu. Rev. Med., 1997, 48: 353-374. [7] R. B. Weiss, R. C. Donehower, P. H. Wiernik, et al. Hypersensitivity reactions from Taxol. J. Clin. Oncol., 1990, 8: 1263-1268. [8] X. L. Zhao, D. W. Chen, P. Gao, et al. Synthesis of ibuprofen eugenol ester and its microemulsion formulation for parenteral delivery. Chem. Pharm. Bull., 2005, 53: 1246-1250. [9] K. M. Park, C. K. Kim. Preparation and evaluation of flurbiprofen-loaded microemulsion for parenteral delivery. Int. J. Pharm., 1999, 181: 173-179. [10] C. Von Corswant, P. Thorén, S. Engström. Triglyceridebased microemulsion for intravenous administration of sparingly soluble substances. J. Pharm. Sci., 1998, 87: 200-208. [11] J. M. Lee, K. M. Park, S. J. Lim, et al. Microemulsion formulation of clonixic acid: solubility enhancement and pain reduction. J. Pharm. Pharmacol., 2002, 54: 43-44. [12] I. F. Uchegbu. The biodistribution of novel 200-nm palmitoyl muramic acid vesicles. Int. J. Pharm., 1998, 162: 19-27. [13] A. Sharma, U. S. Sharma, R. M. Straubinger. Paclitaxelliposomes for intracavity therapy of intraperitoneal P388 leukemia. Cancer Lett., 1996, 107: 265-272. [14] J. Ciccolini, J. Catalin, M. F. Blachon, et al. Rapid highperformance liquid chromatographic determination of docetaxel (Taxotere) in plasma using liquid-liquid extraction. J. Chromatogr. B Biomed. Sci. Appl., 2001, 759: 299-306. [15] M. J. Lawrence, G. D. Rees. Microemulsion-based media as novel drug delivery systems. Adv. Drug Deliv. Rev., 2000, 45: 89-121. [16] A. S. Narang, D. Delmarre, D. Gao. Stable drug encapsulation in micelles and microemulsions. Int. J. Pharm., 2007, 342: 9-25. [17] L. Feng, L. Dexi. Long-circulating emulsions (oil-in-water) as carriers for lipophilic drugs. Pharm. Res., 1995, 12: 1060-1064.

104 Taxotere F1 F2 F3

103

102

101

0

1

2

3

4

5

6

7

Time (h) Fig. 7. Plasma concentration-time profiles of docetaxel after single dose intravenous injection of Taxotere® (●), F1 (○), F2 (▼) and F3 (△) equivalent to a docetaxel dose of 8 mg/kg to rats. Each data point represents the mean ± SD of four determinations.

4. Conclusion The solubility of docetaxel was significantly improved by three microemulsion systems which were optimized using pseudo-ternary phase diagrams. The in vitro cytotoxicity data on three breast cancer cell lines showed that there was no significant difference in the IC50 value among the microemulsion formulations and Taxotere®. Moreover, the pharmacokinetic parameters of docetaxel were altered by microemulsions compared with those obtained with Taxotere®, and this is expected to enhance the antitumor activity of docetaxel in vivo. Thus, the optimized microemulsions may offer an alternative for the delivery of docetaxel with a higher solubility and potential efficacy due to its prolonged exposure in vivo. Nevertheless, more systematic research should be conducted to prove the feasibility of microemulsion delivery systems for parenteral administration.

References [1] K. A. Lyseng-Williamson, C. Fenton. Docetaxel: a review of its use in metastatic breast cancer. Drugs, 2005, 65: 2513-2531.

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