ORIGINAL ARTICLES
Tianjin Key Laboratory of Modern drug Delivery and High-Efficiency, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, PR China
Microemulsion: a novel transdermal delivery system to facilitate skin penetration of indomethacin
Liangmei Chen, Fengping Tan, Jinfeng Wang, Feng Liu
Received November 11, 2011, accepted December 20, 2011 Liangmei Chen, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, PR China [email protected] Pharmazie 67: 319–323 (2012) doi: 10.1692/ph.2012.1150
In this study, we aimed to develop thermodynamically stable microemulsion formulations of indomethacin with lower surfactant and cosurfactant contents, to improve drug permeability. Formulations were based on the oil/water microemulsion region of pseudo-ternary phase diagrams. The characteristic parameters (viscosity, diameter, and polydispersity) of the microemulsion formulations were then determined. In vitro permeation studies were performed using Franz diffusion cells. Permeation through mouse skin and skin retention of indomethacin microemulsions and ointment were tested. The cumulative amount of permeated indomethacin and its skin retention were significantly higher in microemulsion formulations compared with ointment. Drug flux and skin retention improved with decreasing droplet diameter of the microemulsions. On the basis of these results, we suggest some possible mechanisms for the enhanced transdermal permeation of drugs in microemulsions, including high drug-loading capacity, permeation enhancement by surfactants and cosurfactants, and smaller droplet diameter. In conclusion, microemulsions represent a novel transdermal delivery vehicle for increasing the solubility and permeability of indomethacin.
1. Introduction The present study thus aimed to develop a novel microemul- sion containing biocompatible soybean oil and nonionic mixed Microemulsions are transparent, optically isotropic, thermody- surfactants as a transdermal delivery vehicle to enhance the namically stable systems composed of water, oil, surfactant and permeation of indomethacin. cosurfactant (Wu et al. 2001). They have been studied as drug delivery systems because of their capacity to increase the sol- ubility of poorly water-soluble drugs, as well as their ability to 2. Investigations, results and discussion improve topical and systemic drug availability (Lee et al. 2005, 2.1. Phase diagrams 2002). Microemulsions are spontaneously formed, single-phase colloidal dispersions of either oil-in-water (O/W) or water-in- Figures 1, 2 and 3 show the pseudo-ternary phase diagrams with oil (W/O), stabilized by an interfacial film of surfactants and various weight ratios of oil:Smix, with DGME, ETOH or PG as cosurfactants (Gupta et al. 2008). There are several mecha- cosurfactants. The concentration range of components for O/W nisms whereby microemulsions could enhance drug permeation, microemulsions could easily be determined using these phase such as through increased drug-loading capacity and through diagrams. In systems using DGME as cosurfactant (Fig. 1), the the permeation-enhancing abilities of the microemulsion com- area of the O/W microemulsion was larger when the ratios of ponents (Kweon et al. 2004; Peltola et al. 2003). oil:Smix were 1:3 and 1:4. Figure 2 indicates that the area of Indomethacin (IMC) is a poorly water-soluble, non-steroidal the O/W microemulsion was larger when the ratio of oil:Smix anti-inflammatory drug, which is effective for managing con- was 1:4 in the systems using ETOH as cosurfactant, while ditions including rheumatoid arthritis, ankylosing spondylitis, Fig. 3 shows that a 1:5 ratio of oil:Smix had the largest O/W and osteoarthritis (Chauhan et al. 2003). Oral therapy with microemulsion region when PG was used as the cosurfactant. indomethacin is very effective, but its clinical use is often limited Five microemulsion formulations were selected on the basis of by its potential adverse effects, such as nephrotoxicity, and irrita- these phase diagrams, as described in Table 1. tion and ulceration of the gastrointestinal mucosa (Beetge et al. 2000). Transdermal administration of indomethacin bypasses disadvantages associated with the oral route, and can result in 2.2. Characterization of the selected microemulsion the maintenance of relatively consistent long-term plasma levels formulations following a single dose. Several commercial products have been The characteristic parameters of the microemulsions are developed to enhance the permeation of indomethacin, including reported in Table 2. The average diameter of all microemul- ointment, patches and liniment. In this study, indomethacin was sions ranged from 104Ð305 nm, and the polydispersity was incorporated into a microemulsion system to improve its low < 0.5 in all cases. The viscosities of the microemulsions E solubility and permeability, which are key issues in the design and F were 526.62 ± 25.47 mPa.s and 436.47 ± 19.61 mPa.s, of transdermal delivery systems. respectively, which were higher than those of formulations AÐD Pharmazie 67 (2012) 319 ORIGINAL ARTICLES
Fig. 1: Pseudo-ternary phase diagrams of systems with DGME as cosurfactant (oil:Smix were 1:3, 1:4 and 1:5, respectively.) (Table 2). Comparing the microemulsions E and F with the tive permeated indomethacin with time was observed, with the other formulations (AÐD), it was obvious that the viscosity permeation profiles following zero order kinetics. The cumu- increased significantly with increasing oil and surfactant con- lative permeated amounts from microemulsions AÐF at 12 h tents (Tables 1, 2). application ranged from 107.79Ð197.31 g.cm−2, while that from the control (ointment) was only 16.07 g·cm−2. These results indicate that a microemulsion system was able to sig- 2.3. In vitro skin permeation studies nificantly (P < 0.05) improve the permeability compared with Figure 4 shows the permeation profiles of indomethacin through the ointment. mouse skin using the selected microemulsion formulations, with Figure 5 shows the permeation flux and skin retention of commercial ointment as a control. A steady increase in cumula- indomethacin in relation to the droplet diameter of the selected
Fig. 2: Pseudo-ternary phase diagrams of systems with ETOH as cosurfactant (oil:Smix were 1:3, 1:4 and 1:5, respectively.)
320 Pharmazie 67 (2012) ORIGINAL ARTICLES
Fig. 3: Pseudo-ternary phase diagrams of systems with PG as cosurfactant (oil:Smix were 1:3, 1:4 and 1:5, respectively.)
Table 1: Compositions of the microemulsion formulations microemulsion formulations that directly affects the transdermal (w/w, %) skin delivery of indomethacin. There are several possible mechanisms whereby microemul- IMC SO Smix DGME EtOH PG Water sions could enhance drug permeation for transdermal delivery. Firstly, the mechanism may be related to the high drug-loading A 1 6.60 19.80 24.75 Ð Ð 47.85 capacity of microemulsions (Kreilgaard 2002). The solubility B 1 5.45 21.78 27.22 Ð Ð 44.55 of indomethacin in the surfactants and cosurfactants was higher C 1 7.26 21.78 27.22 Ð Ð 42.74 than in water and soybean oil (data not shown). It is possible that D 1 5.94 23.76 29.70 Ð Ð 39.60 most indomethacin accumulated at the droplet interfaces, rather E 1 10.0 40.0 Ð 11.43 Ð 37.57 F 1 6.0 30.0 Ð Ð 30 33.0 than staying in the oil or continuous phase. The indomethacin content in the selected microemulsion formulations was about 340 times higher than that in water. This high drug concentra- tion would result in a high concentration gradient, which might formulations. The data for flux and skin retention are listed account for its increased skin permeation. in Table 2. Both flux (Fig. 5a) and skin retention (Fig. 5b) Secondly, surfactants and cosurfactants in the microemulsion decreased with increasing droplet diameter of the formulation. may reduce the diffusional barrier of the stratum corneum by act- The diameters of the formulations were ranked as follows: ing as permeation enhancers (Huang et al. 2008; Bolzinger et al. B
Table 2: Characteristics and permeation parameters of various formulations
Formulation Viscositya (mPa.s) Diametera (nm) Polydispersitya Fluxb (g.cm−2.h−1) Skin Retentionb (g.mg−1)
A 64.45 ± 3.13 184.7 ± 1.9 0.318 ± 0.007 14.99 ± 0.61* 0.65 ± 0.036* B 104.84 ± 4.38 104.0 ± 0.4 0.375 ± 0.004 21.45 ± 1.88* 0.72 ± 0.035* C 95.46 ± 4.21 227.0 ± 1.2 0.289 ± 0.01 14.31 ± 0.37* 0.61 ± 0.032* D 110.90 ± 5.52 305.3 ± 4.0 0.306 ± 0.011 12.79 ± 0.98* 0.55 ± 0.025* E 526.62 ± 25.47 137.3 ± 0.5 0.285 ± 0.004 16.85 ± 0.36* 0.67 ± 0.034* F 436.47 ± 19.61 229.1 ± 3.1 0.242 ± 0.006 13.99 ± 0.42* 0.59 ± 0.026* Control Ð Ð Ð 1.57 ± 0.24 0.18 ± 0.011 a: mean ± SD, n = 3; b: mean ± SD, n = 6. * P < 0.05, when compared with control.
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Fig. 4: Permeation profiles of indomethacin through mouse skin using various Fig. 5: Relationships between permeated flux (a) and skin retention (b) of formulations (ointment), mean ± SD,n=6 indomethacin and microemulsion diameter, mean ± SD,n=6
(Gamal et al. 2008). The small droplet size produced by the surfactants and cosurfactants means that the microemulsion pro- molecules to more easily permeate into the stratum corneum. vides a very large area for the drug, which is distributed within The results of this study demonstrate that the droplet diameter of the nanostructure of the system. Usual surfactants are unable the microemulsion is a critical factor determining the permeation to lower the interfacial tension between the oil and water to of indomethacin through mouse skin (Fig. 5, Table 2). such ultra-low values, and a cosurfactant is frequently neces- Safety is also a critical factor of transdermal delivery sys- sary (Trotta 1999). Incorporation of cosurfactant can further tems. All the components of the microemulsion formulations reduce the interfacial tension between the oil and water in the selected in this study had low irritant and toxicity characteris- microemulsion, adjust the flexibility of the interfacial mem- tics; however the content of surfactant mixture was 30Ð40% in brane, and reduce the amount of surfactant required (Lee et al. formulations E and F, which would increase the skin irritation. 2003). Among the six microemulsion formulations in this study, Thus, although E and F demonstrated high permeation abili- DGME, ETOH and PG were investigated as alternative cosurfac- ties, they would be unsuitable for chronic skin application for tants. The solubility of indomethacin with DGME as cosurfac- safety reasons (Chen et al. 2004). Formulation B, which had ± · −1 tant was 133.12 2.63 mg ml , which was much higher than the highest permeation flux in association with a lower content with EtOH or PG. Thus, as indicated in Table 1, DGME reduced of surfactant mixture, was selected as the optimum formulation. the amount of surfactant required significantly more than EtOH This formulation should be further investigated in future studies. or PG. Meanwhile, DGME could also help the surfactant to reduce the interfacial tension between the oil and water in the microemulsion more efficiently than EtOH or PG. Formulation 3. Experimental B had the lowest contents of surfactant and cosurfactant and the highest permeation flux (21.45 ± 1.88 g·cm−2·h−1) of the six 3.1. Materials microemulsion formulations (Table 2). Indomethacin was purchased from Shijiazhuang Pharmaceutical Group The small droplet diameter of microemulsions means that the Huasheng Pharma Co., Ltd. (Herbei, China). Soybean oil (SO) was pur- chased from Tieling Beiya Medicinal Oil Co., Ltd. (Liaoning, China). oily droplets might enter the stratum corneum, and the drug Cremophor EL was purchased from BASF (Germany). Span 80, diethylene molecules could thus be delivered directly from these droplets glycol monoethyl ether (DGME), absolute ethanol (EtOH), and propylene into the stratum corneum, with no transfer via the hydrophilic glycol (PG) were purchased from Jiangtian Chemical Technology Co., Ltd. phase of the microemulsion (Mou et al. 2008), allowing drug (Tianjin, China). 322 Pharmazie 67 (2012) ORIGINAL ARTICLES
3.2. Construction of pseudo-ternary phase diagrams 3.6. HPLC analysis of indomethacin Soybean oil was selected as the oil phase on the basis of its good biocom- The concentration of indomethacin was analyzed using an HPLC system patibility with skin. Various surfactants were screened in our preliminary consisting of a Series III pump and a Model 201+ UV detector (LabAl- studies, and Cremophor EL/Span 80 was chosen as the mixed surfactant liance, US). The column was a reversed-phase Kromasil C18 column (Smix) for the soybean oil phase. (250 mm × 4.6 mm internal diameter, 5 m, LabAlliance). The mobile phase Pseudo-ternary phase diagrams were constructed by aqueous solution titra- was a mixture of 0.1 mol·L−1 acetic acid and methanol (20:80, v/v) flowing tion at ambient temperature (25 ◦C) to obtain the concentration ranges of at1ml·min−1. The detection wavelength was 228 nm. components for the microemulsions, without the drug (Huang et al. 2008). Firstly, oil and Smix were mixed at certain weight ratios (1:3, 1:4, and 1:5) and the mixtures of oil/Smix and cosurfactant were then titrated dropwise References with water, under gentle magnetic stirring, at weight ratios of 1:9, 2:8, 3:7, Beetge E, Plessis J, Muller DG, Goosen C, Rensburg FJ (2000) The influ- 4:6, 5:5, 6:4, 7:3, 8:2 and 9:1. After equilibration, the systems were iden- ence of the NSAID’s on their transdermal absorption. Int J Pharm 193: tified visually and determined as transparent fluid microemulsions, crude emulsions, or gels. Based on these phase diagrams, the microemulsion for- 261Ð264. mulations with the desired component ratios were selected and tested as Bolzinger MA, Briancon S, Pelletier J, Fessi H, Chevalier Y (2008) Percu- indomethacin-containing microemulsions. taneous release of caffeine from microemulsion, emulsion and gel dosage forms. Eur J Pharm Biopharm 68: 446Ð451. Chauhan AS, Sridevi S, Chalasani KB, Jain AK, Jain SK, Jain NK, Diwan 3.3. Preparation of microemulsions PV (2003) Dendrimer-mediated transdermal delivery: enhanced bioavail- After identification of the microemulsion regions in the phase diagrams, ability of indomethacin. J Control Release 90: 335Ð343. formulations were selected at different component ratios, as described Chen H, Chang X, Weng T, Zhao X, Gao Z, Yang Y, Xu Y, Xu H, Yang in Table 1. The microemulsions were prepared, briefly as follows: X (2004) A study of microemulsion systems for transdermal delivery of indomethacin was added to mixtures of soybean oil, surfactant, and cosur- triptolide. J Control Release 98: 427Ð436. factant at various component ratios, and water was then added to the above Cross SE, Jiang R, Benson HAE, Roberts MS (2001) Can increasing mixtures drop by drop, with magnetic stirring for 30 min at ambient tem- the viscosity of formulations be used to reduce the human skin pen- perature, until all the microemulsions were transparent. etration of the sunscreen oxybenzone. J Invest Dermatol 117: 147Ð 150. 3.4. Characterization of the selected microemulsion formulations Cross SE, Roberts MS (2000) The effect of occlusion on epidermal pene- The average diameters and polydispersity indexes of the microemulsion tration of parabens from a commercial allergy test ointment, acetone and formulations were measured using ZetaPALS (Brookhaven Instrument Cor- ethanol vehicles. J Invest Dermatol 115: 914Ð918. poration, US) at 25 ◦C. The viscosities of the microemulsion formulations Gamal M, Maghraby E (2008) Transdermal delivery of hydrocortisone from were determined using an Ubbelohde viscometer (Glass Instrument Factory eucalyptus oil microemulsion: Effects of cosurfactants. Int J Pharm 355: ◦ of Taizhou, Zhejiang Province, China) at 25 C. 285Ð292. Gupta S, Moulik SP (2008) Biocompatible microemulsions and their 3.5. In vitro skin permeation studies prospective uses in drug delivery. J Pharm Sci 97: 22Ð45. Huang YB, Lin YH, Lu TM, Wang RJ, Tsai YH, Wu PC (2008) Trans- Abdominal skin was obtained from male Kunming mice weighing 25 ± 2g. Mice were sacrificed and hair was removed using clippers. Skin was then dermal delivery of capsaicin derivative-sodium nonivamide acetate using excised from the abdominal region, and subcutaneous fat and other tissues microemulsions as vehicles. Int J Pharm 349: 206Ð211. were trimmed. Skin samples were stored at −20 ◦C prior to use. Kreilgaard M (2002) Influence of microemulsions on cutaneous drug deliv- The experiments were performed using vertical Franz diffusion cells (Phar- ery. Adv Drug Deliv Rev 54: S77Ð98. macopoeia Standard Instrument Factory of Tianjin, China) with 1.77 cm2 Kweon J H, Chi SC, Park ES (2004) Transdermal delivery of diclofenac of diffusion area. Full-thickness skin was mounted between the donor using microemulsions. 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A defined amount of methanol was then Trotta M (1999) Influence of phase transformation on indomethacin release added to each piece of skin, the samples were homogenized, centrifuged at from microemulsion. J Control Release 60: 399Ð405. 12,000 g, and the concentrations of indomethacin were analyzed by HPLC. Wu H, Ramachandran C, Weiner ND (2001) Topical transport of hydrophilic Skin retention experiments were performed to analyze the skin content of compounds using water-in-oil nanoemulsions. Int J Pharm 220: indomethacin after 12 h of diffusion. 63Ð75.
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