Feasibility Experiments for the Development of Innovative Transdermal Systems

Contents

1. List of Figures

2. List of Tables

3. List of abbreviations

4. Introduction

5. Theoretical background
5.1 The barrier of the skin and transdermal therapeutic systems
5.2 Transdermal therapeutic systems in combination with microneedles
5.3 In-vitro skin permeation tests

6. Materials and methods
6.1 Chemicals and reagents
6.2 Methods
6.2.1 API coating
6.2.2 Skin preparation
6.2.3 Skin perforation
6.2.4 Verifying the integrity and perforation of the skin
6.2.5 Penetration assessment
6.2.6 In-vitro skin permeation tests

7. Statistical analysis

8. Results
8.1 Skin perforation tests
8.2 In-vitro skin permeation tests

9. Discussion and conclusion

10. Sources

Acknowledgements

This research was supported by tesa Labtec GmbH in Langenfeld.

Firstly, I would like to express my sincere thanks to my academic supervisor Dr. Evert Vanecht and my business supervisor Dr. Armin Breitenbach for their support of my BA­Thesis.

My appreciation also goes to Dr. Frank Fischer (Beiersdorf AG) and Dr. Nicolai Böhm (tesa SE), who provided me an opportunity to join their team and gave access to the laboratory and research facilities. Without their precious support it would not have been possible to conduct this research.

I thank Sonja Pagel-Wolff, Daniel Mellem and Thomas Lange from Beiersdorf AG; who provided insight and expertise that greatly assisted the research regarding the microscopic technology, Christiane Uhl from Courage+Khazaka electronic GmbH, who provided insight and expertise concerning the TEWL-Technology, and Sebastian Schmidt- Lehr from tesa SE, who provided insight and expertise regarding Micro-CT-technology.

I thank Sandra Lindert, Gabriele Stodt and Marion Tegelkamp for the stimulating discussions.

Last but not least, I would like to thank Eva Kerski for supporting me during this thesis.

Abstract

Transdermal therapeutic systems (TTS) are dosage forms developed to transport an active pharmaceutical ingredient (API) through the skin. This is done by applying a patch to the skin and is therefore a pain-free method. Since the establishment of this method, TTS have been a good alternative to traditional dosage forms such as tablets, injection needles and suppositories.

However, there is a crucial limit to TTS. APIs which are significantly greater than 500Da (500g/mol) cannot pass through the skin barrier. As several publications (cf. Cormier et al., 2004, Roxhed, 2007 and Yu et al., 2015) have shown, there is a possibility to transport APIs which are greater than 500Da through the skin. Combining TTS with microneedles (MN) is a way to produce microchannels through which the API can then pass the skin barrier. The aim of this work was to test the in-vitro permeability of APIs across perforated and unperforated skin. Both, traditional adhesive matrices and hydrogel matrices were developed and tested. The result of this work is that it is possible to deliver model substances greater than 500Da through the skin barrier by perforating the epidermis. Customary MN systems were not sufficient to perforate the skin barrier. Hypodermic needles, however, are suitable to perforate the stratum corneum (SC). Consequently, the combination of TTS technology with MN technology is possible and should be further developed. Nevertheless, suitable MN have to be found. Hollow needles which are incorporated into a hydrogel matrix are a very promising option for a future product.

1. List of Figures

All figures are my own work. They were either plotted using the respective programme or MS Office 2007 and 2010

Figure 1: SC with its main constituents, the dead corneocytes

Figure 2: conceptual drawing of different ways of permeation of the APIs through the skin

Figure 3: conceptual drawing of a matrix TTS (A) and a reservoir TTS (B)

Figure 4: conceptual drawing of a microneedle-based drug delivery system applied to the surface of the skin

Figure 5: images of the preparation of a TTS, (A) preparing of the hydrogel, (B), (C), (D) & (E) distribution by squeegee, (F) distributed hydrogel matrix

Figure 6: conceptual drawing of the implementation of the perforation

Figure 7: images of ex-vivo human skin in the SKYSCAN (A) & after measuring, surface and side view (B)

Figure 8: conceptual drawing of the Permeation cell by Kerski, Rathsack and Stodt

Figure 9: TEWL in g/h/m2 in-vivo skin, after penetration with "Derma Stamp Electric Pen" Manufacturers MYM. Right arm (B) and left arm (C) vs Reference (A) unperforated skin. Error bars indicate SD (n = 2)

Figure 10: TEWL in g/h/m2 and capacitance measurement (Corneometer®) after perforating ex-vivo skin when using "Derma Stamp Electric Pen". (A) and (C) full thickness skin, (B) and (D) split thickness skin. Error bars indicate SD (n = 6)

Figure 11: images of (A) freshly treated skin, (B) treated skin after 3.5h, (C) high resolution laser scanning microscope illustration of freshly treated skin

Figure 12: images of (A) MN of MYM stamp before perforation, (B) MN of MYM stamp after perforation and (C) hyperdermic needle (no change after peforation). 26 Figure 13: image of in-vivo human skin; recording depth (A) 73,9pm, (B) 7,82pm, (C) 16,0pm, (D) 2,0pm, (E) 34pm, (F) 100,0pm, (G) 0,0pm, (H) 28,2pm, (I) 56,0pm

Figure 14: images of ex-vivo human skin (A) untreated skin possibly dried and (B) treated skin, before the measurement (water replaced with PEG)

Figure 15: Mass balance of the different formulations of the TTS after IVSP vs. TTS from the assay of the API. The results underline the suitability of the model. Error bars indicate SD (n = 6)

Figure 16: Permeation kinetics. Error bars indicate SD (n = 6)

2. List of Tables

Table 1: Selected settings for the measurements at the 5D-IVT

Table 2: Comparison of the permeation parameters of the four formulations

3. List of abbreviations

Abbildung in dieser Leseprobe nicht enthalten

4. Introduction

This bachelor thesis deals with the development of a new system for Transfilm®, the TTS technology of tesa Labtec (tL). TTS are drug delivery systems that are applied directly to the skin. The active substance is absorbed by the skin and distributed through the body via the bloodstream. The advantage of Transfilm® is that it allows a safe, reliable, precise and pain- free application with fewer side effects (cf. Gronbach, A., & Kerski, S., 2012). Thus, it becomes easier to treat children, as well as elderly patients and patients requiring complex care. The fact that the transdermal patch can provide a controlled release of medication for up to seven days gives it a major advantage over other types of drug delivery.

To date, there are ca. 20 APIs for which TTS technology has been established (cf. Roxhed, 2007, p. 6). However, many APIs cannot pass the epidermis because of their size. In order to increase the permeability of APIs, there have been many approaches.

One of the greatest challenges for tL is the development of new transdermal systems. An innovative possibility is the combination of TTS with MN. The main motivation to use MN is that systemic absorption can be achieved under minimally invasive conditions in cases where regular passive diffusion technologies are not effective enough.

The aim of this paper is to present first experiments for an innovative development of TTS in combination with MN in order to discern the prospects of further projects. The aim is not to define a ready-for-market formula. First, a suitable MN technology needed to be found to make sure that the SC is perforated while the dermis stays intact. Furthermore, TTS formulations were tested to detect how much API is released through the microchannels from a hydrogel matrix or a silicone matrix in order to determine the matrix system that is particularly suited for this technology.

The next chapter describes the theoretical background of the tests. This chapter gives relevant information on the structure of the human skin and TTS and MN technologies. Chapter 6 contains an overview of the used materials and the methods that were employed to test the perforation of the skin and the API release from different matrices. The following chapter (7) comprises statistical analyses of the test results. After that, the results are presented in chapter 8. These are discussed in the final chapter 9.

5. Theoretical background

5.1 The barrier of the skin and transdermal therapeutic systems

This paper primarily deals with Transfilm®, the TTS of tL. TTS are drug delivery systems that are applied directly to the skin. To understand the mechanism of a TTS, it is important to know the structure of the skin. The SC is the barrier of the skin and protects the underlying tissues from heat, microbes and chemicals. Below the epidermis there are basal layers, which serve epidermal wound healing and form a new SC through keratinization (cf. Tortora & Derrickson, 2006, p. 191).

According to recent research the dermis does not function as a barrier for APIs or any other substances. For this reason only the barrier properties of the SC are considered in the context of this thesis. Figure 1 shows a simplified sketch of the skin (cf. Tortora & Derrickson, 2006 p. 191 & 193). The mechanical resistance of the epidermal barrier is mainly due to the corneocytes embedded in the so called cornified envelope. The main biochemical components of the skin barrier are lipids and proteins (cf. Darlenski et al., 2011, p.37).

Abbildung in dieser Leseprobe nicht enthalten

The API is absorbed by the skin and distributed through the body via the bloodstream. The advantage of the Transfilm® is that it allows a safe, reliable, precise and pain-free application providing fewer side effects (cf. Gronbach, A., & Kerski, S., 2012, p. 1). Thus, it becomes easier to treat children, as well as elderly patients and patients requiring complex care. The fact that the TTS provide a controlled release of medication for up to seven days gives it a major advantage over other drug delivery systems. A well-known TTS is the nicotine patch. Another product which is already on the market is a patch containing fentanyl, an API used in the treatment of chronic cancer pain (Fentanyl Ratiopharm). The fentanyl patch was developed and has always been manufactured by tL (Kerski et al, 2009, p.7). Other cases in which TTS are used are Morbus Parkinson, Morbus Alzheimer and Angina Pectoris (cf. Sharma, R., Puri, D., Bhandari, A., Soni, B., & Singh, M. 2011).

The API should not exceed a certain size (approx. 500Da) so that it can penetrate the skin effectively (cf. Bos, J. D., & Meinardi, M. M., 2000). Furthermore, the active substance should be lipophilic enough to penetrate the skin, but at the same time has to be hydrophilic enough to get into the bloodstream. There is a distinction between three different ways of permeation of APIs through the skin. APIs do not only pass through pores and hair follicles (follicular), but also through microscopic intercellular spaces or through the cells themselves (intracellular).

All three routes are displayed graphically in Figure 2.

Abbildung in dieser Leseprobe nicht enthalten

Figure 2: conceptual drawing of different ways of permeation of the APIs through the skin.

On the intercellular route, the API migrates through a lipid matrix which is located between the corneocytes (cf. Chien, Y W., 1993, p. 132). This is only possible if the API has lipophilic characteristics. To date, there are 20 active substances known to fulfill these requirements (cf. Roxhed, 2007, p. 6). Many APIs cannot pass the epidermis because of their size. Large molecules like peptides or proteins, particularly insulin or vaccines, are therefore not suited to be applied with a patch so far. In order to increase the permeability of drugs many approaches have been described (cf. Barry, 1993, p.119 and Chien, 1993). All of them have tried to enhance the permeability of the SC. For example, chemical enhancers reversibly disrupt the SC structure.

Different APIs require different designs. In general, one can distinguish between two types of transdermal patches (see Figure 3). The matrix system (A) is a semisolid adhesive matrix, a solution or suspension containing an API. The reservoir TTS (B) has a separate API layer. The API layer is a liquid compartment containing a drug solution or suspension separated from the adhesive layer by a membrane. Both types of patches deliver a specific dose of API through the skin and into the bloodstream (cf. Sharma, R., Puri, D., Bhandari, A., Soni, B., & Singh, M., 2011). Figure 3 shows the different types of TTS (cf. Kalvimoorthi, Rajasekaran, Rajan, Balasubramani, & Kumar).

Abbildung in dieser Leseprobe nicht enthalten

Figure 3: conceptual drawing of a matrix TTS (A) and a reservoir TTS (B).

5.2 Transdermal therapeutic systems in combination with microneedles

One of the greatest challenges for tL is the development of new TTS. One innovative possibility is the combination of TTS and MN. MN are long enough to penetrate the outer layer of the skin but too short to irritate nerves and blood vessels. They can be used to deliver APIs with larger molecules into the skin, an application that is largely pain-free. MN create tiny holes in the outermost layer of the skin (cf. Donnelly et al., 2010, p. 337), which significantly increases the rate at which the active substance is absorbed (cf. Kim et al., 2012, p. 1562). The main motivation to use MN is that systemic absorption can be achieved under minimally invasive conditions in cases where regular passive diffusion technologies are not effective enough. So far, numerous commercial MN systems are available, which are used in medical or cosmetic contexts. The first official product on the market was the so called Dermaroller® (cf. mi.to.pharm-GmbH, 2015). According to Roxhed (cf. Roxhed, 2007, p. 23) the first publication on solid MN was delivered by Dizon, Han, Russell, & Reed (1993) and the first paper about hollow MN was submitted by Mc Allister et al. (1999). MN can be used to inject active substances with small or large molecules into the skin (cf. Badran, Kuntsche, & Fahr, 2009). The first patent of a TTS combined with MN was published by Gerstel (cf. Gerstel & Place, 1976).

Abbildung in dieser Leseprobe nicht enthalten

Figure 4: conceptual drawing of a microneedle-based drug delivery system applied to the surface of the skin.

While the application is largely pain-free, it still causes minimal reversible injuries of the epidermis resulting in the exudation of hydrophilic fluids. Traditional matrix systems, however, usually contain lipophilic adhesive matrices based on, for example, acrylate, silicone or styrene. A hydrophilic matrix system might be better suited for a combination of TTS with MN, because in this case the matrix as well as the exuded fluids are hydrophilic. Beiersdorf AG already offers various wound plasters under the name of Hansaplast® and also holds patents on a hydrogel matrix system, which is suitable for transdermal patches (cf. Wöller, 2013).¹

5.3 In-vitro skin permeation tests

In-vivo experiments are the best model to test whether the API can permeate through the skin barrier. As an alternative to this method, this thesis contains in-vitro skin permeation tests (IVSP) in an artificial environment. The term in-vitro (from Latin; vitrum = glass) means the transfer of experiments outside of the organism, for example into test tubes. The term ex-vivo (from Latin; vivus = living) is also used for skin permeation experiments as they are not conducted on living organisms. This term highlights the collection of material from a living organism.

According to the guidelines by the European Medicines Agency (EMA) (2014) and the Organisation for Economic Cooperation and Development (OECD) (2004), IVSP-studies are not expected to parallel in-vivo release. IVSP-studies ensure the comparability of an original TTS with development batches that were characterized during the development process and reflect the thermodynamic activity of the API. As part of this thesis, IVSP-tests were performed. The IVSP is a simple and often used test during TTS development. The experiments were performed using a permeation-cell developed at tL (cf. Kerski et al., 2015) which is a further modification of the permeation-cell by Franz (cf. Franz, 1975). The Franz cell consists of a donor compartment in which solutions or patches can be applied to the skin surface. Underneath, there is an acceptor compartment filled with an aqueous buffer. The active substance diffuses from the donor chamber through the skin into the acceptor chamber. Via the sampling port, the sample is taken in regular intervals and replaced by fresh medium. The API concentration in the sample is measured by HPLC.

This makes it possible to trace the permeation of the API through the skin throughout the selected period of time. The temperature stays constant at 32°C (physiological temperature of the skin) during this period (cf. EMA, 2014, p. 25 and OECD, 2004, p. 4). The IVSP is an important method in dosage form approval. For this reason, the EMA added Appendix 1 to the Guideline on quality of transdermal patches in 2014 (cf. EMA, 2014). The IVSP-tests in this thesis were performed according to the guidelines of EMA and OECD. According to the OECD, the principal diffusion barrier for the API is the non-viable SC (cf. OECD, 2004, p. 1). Damage to the epidermis can be very well observed visually and evaluated. A sampling longer than 24 hours is allowed if the sampling frequency of the receptor fluid allows the absorption profile of the test substance to be presented graphically (cf. OECD, 2004 p. 4).

6. Materials and methods

6.1 Chemicals and reagents

Glycerol 85% Ph. Eur 7.0 and Agar Agar PLV. Ph. Eur 7.0 were purchased from Caesar & Lorenz (Hilden, Germany). Sodium hydroxyde purum 98%, Fluorescein isothiocyanate-dextran average mol wt 4,000, Citric acid monohydrate puriss pa Ph. Eur., Sodiumphosphat puriss pa Ph. Eur, Potassium Phosphate monobasic pa ACS Ph. Eur and Desmopressine European Pharmacopoeia were obtained from Sigma Aldrich (Steinheim, Germany). Carbopol 971 PNF polymer was purchased from Cabrizol Advances (Brussels, Belgium). Purified Water was prepared by filtration of osmosis using the Milli-Q- system from Millipore Advantage A 10 (Darmstadt, Germany). BIO-PSA 7-4201 silicone adhesives were obtained from Dow Corning GmbH (Wiesbaden, Germany). As a liner for the patch preparation Silphan Liner Siliconature SpA (Godega di Sant'Urbano, Italy), HOSTAPHAN® RNT 23 Liner Mitsubishi Polyester Film GmbH (Wiesbaden, Germany) and 3M™ 9733 Scotchpak Backing liner 3M Germany (Neuss, Germany) were used.

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¹ Hydrogel matrix systems for the administering of APIs are traditionally used in Asia, particularly in Japan. The Japanese Pharmacopoeia defines the term "Cataplasma" (poultice).