In Situ Gelling Nasal Inserts for
`Prolonged Drug Delivery
`
`
`
`
`
`Inaugural-Dissertation
`zur Erlangung der Doktorwürde
`im Fachbereich Biologie, Chemie, Pharmazie
`der Freien Universität Berlin
`
`
`
`vorgelegt von
`Ulrike Werner
`
`
`
`Berlin 2003
`
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`1. Gutachter: Prof. Dr. Roland Bodmeier
`
`2. Gutachter: Prof. Dr. Philippe Maincent
`
`Tag der mündlichen Prüfung: 19.11.2003
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`Acknowledgements
`
`
`First of all, I wish to express my gratitude to my supervisor, Prof. Dr. Roland Bodmeier, for
`his kind supervision, his helpful advice and professional guidance, for providing this
`interesting research topic and his scientific support. It was a great experience and pleasure to
`study, to work and to do research in his international group.
`
`I deeply thank Prof. Dr. Philippe Maincent (Faculté de Pharmacie, Université Poincaré,
`Nancy, France) for useful discussions and for his evaluation of my thesis. I am also very
`grateful to Dr. Christiane Damgé (Centre Européen d'Etude du Diabète, Université Louis
`Pasteur, Strasbourg, France). The opportunity to work in her research group was extremely
`valuable for me and my studies.
`
`I would like to thank all the helpful people at the Free University Berlin for giving me the
`opportunity to use advanced methods of instrumental analytics and their kind help in data
`interpretation: Priv.-Doz. Dr. Gerd Buntkowsky and Thomas Emmler (Institute of Chemistry)
`for performing the 13C-CP/MAS NMR measurements, Prof. Ronald Gust and Ingo Ott
`(Institute for Pharmacy) for atom absorption spectroscopy studies, Bernhard Behrens
`(Institute for Chemistry) for atom emission spectroscopic measurements, Priv.-Doz. Dr. Wolf-
`Dietrich Hunnius (Institute for Chemistry) for performing FT-Raman investigations, Dr.
`Volker Bähr and Petra Exner (University Hospital B. Franklin) for the support with
`radioimmunoassays, and Dr. Christine Prusas (Institute for Poultry diseases) for providing
`chicken erythrocytes.
`
`Furthermore, I am grateful to Prof. Dr. Ronald Gust, Prof. Dr. Hans Hubert Borchert, Priv.-
`Doz. Dr. Ralph Lipp, Dr. Wolfgang Mehnert and Boris Petri for serving as members of my
`thesis advisor committee.
`
`I sincerely wish to thank Dirk Sticha, Heike Friedrich, Oliver Bley, Katrin Johannsen, Mesut
`Ciper, and all my friends and colleagues in the Kelchstraße for their support, proof-readings,
`constructive discussions in early Monday seminars and the stimulating and enjoyable
`atmosphere in the group. I am grateful to Dr. Jürgen Siepmann for his readiness to discuss my
`work and his valuable suggestions. Special thanks go also to Andreas Krause and Eva Ewest
`for their support and to Angelika Schwarz for her help in the jungle of university bureaucracy.
`
`Finally, I want to thank Matthias and my family for their love and support through the years
`and their never-ending encouragement and confidence in me.
`
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`___________________________________________________________________________
`
`
`Table of Contents
`
`
`1. INTRODUCTION………………………………………………………………….. 1
`1.1. Transmucosal routes of drug delivery.…………………………………….….. 1
`1.1.1. Nasal drug delivery…………………………………………………….…. 3
`1.1.2. Buccal drug delivery………………………………………………….…... 4
`1.1.3. Ocular drug delivery…………………………………………………..….. 4
`1.1.4. Pulmonary drug delivery…………………………………………...…..… 6
`1.1.5. Rectal drug delivery………………………………………………….…... 7
`1.1.6. Vaginal drug delivery………………………………………………….…. 8
`1.1.7. Comparison of transmucosal drug delivery routes…………………….…. 8
`1.2. Nasal anatomy and physiology……………………………………………….... 12
`1.2.1. Anatomy and air passage……………………………………………….… 12
`1.2.2. Physiology…………………………………………………………….….. 13
`1.2.3. Nasal pathology with relevance to nasal drug absorption…………….….. 20
`1.2.4. The nose as drug delivery site: advantages, barriers, and solutions….…... 21
`1.3. The concept of bioadhesion……………………………………………………. 24
`1.4. Nasal vaccination…………………………………………………………….…. 27
`1.4.1. Nasal immunology…………………………………………………….….. 27
`1.4.2. Nasal vaccine delivery……………………………………………….….... 29
`1.5. Nasal drug delivery systems………………………………………………….... 34
`1.5.1. Nasal solutions as drops or sprays………………………………………... 36
`1.5.2. Viscous nasal solutions and gels including bioadhesive solutions……….. 38
`1.5.3. Nasal suspensions and emulsions…………………………………….…... 41
`1.5.4. Nasal micellar and liposomal formulations…………………………….… 42
`1.5.5. Nasal powders and microparticles………………………………………... 43
`1.5.6. Nasal solid dosage forms……………………………………………….… 48
`1.6. Research objectives…………………………………………………………….. 49
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`2. MATERIALS AND METHODS………………………………………………….... 51
`2.1. Materials……………………………………………………………………...… 51
`2.2. Methods……………………………………………………………………….… 52
`2.2.1. General data presentation in diagrams and tables………………………... 52
`2.2.2. Preparation of samples………………………………………………….... 52
`2.2.3. Polymer solution rheology………………………………………….……. 54
`2.2.4. Spreading of polymer solutions……………………………………….….. 55
`2.2.5. Bioadhesion…………………………………………………………….… 55
`2.2.6. Water uptake and mass loss…………………………………………….… 55
`2.2.7. Moisture sorption……………………………………………………….… 56
`2.2.8. Contact angle……………………………………………………………... 57
`2.2.9. Polymer-drug precipitation…………………………………………….…. 58
`2.2.10. In vitro drug release…………………………………………………….… 58
`2.2.11. Release of MβCD……………………………………………………….... 62
`2.2.12. Flame absorption and flame emission spectroscopy…………….……….. 62
`2.2.13. Scanning electron microscopy (SEM)……………………….…………… 63
`2.2.14. Differential scanning calorimetry (DSC)………………….……………... 63
`2.2.15. Powder X-ray diffraction………………………………………….……… 63
`2.2.16. 13C Nuclear magnetic resonance spectroscopy (13C CP/MAS NMR)…..... 64
`2.2.17. FT-Raman spectroscopy…………………………………………………. 64
`2.2.18. Mechanical properties………………………………………………….… 64
`2.2.19. Hemagglutination test………………………………………………….…. 65
`2.2.20. In vivo studies………………………………………………………….…. 65
`
`3. RESULTS AND DISCUSSION………………………………………………….…. 69
`3.1. Influence of the polymer type……………………………………………….…. 69
`3.1.1. Sponge-structure formation……………………………………………..... 69
`3.1.2. Polymer solution rheology…………………………………………….…. 71
`3.1.3. Effect of polymer type on nasal insert properties…………………….…... 75
`3.2. Drug release rate control………………………………………………….…… 85
`3.2.1. Polymer content…………………………………………………………... 85
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`3.2.2. Freely water-soluble additives……………………………………………. 88
`3.2.3. Polymer molecular weight………………………………………………... 91
`3.2.4. Polymer blends………………………………………………………….... 99
`3.3. Effect of drug and release medium on drug release……………………….…. 108
`3.3.1. Influence of drug species and drug loading…………………………….… 108
`3.3.2. Influence of release medium……………………………………………... 115
`3.4. Estradiol delivery…………………………………………………………….… 121
`3.5. Nasal influenza vaccination………………………………………………….… 138
`3.5.1. In vitro properties of polymer solutions………….…………...……….…. 138
`3.5.2. In vivo performance of polymer solutions………………….…………..... 143
`3.5.3. Formulation and in vitro properties of nasal inserts………………..…….. 146
`3.5.4. Hemagglutination activity in solutions and inserts………………………. 149
`3.5.5. In vivo performance of nasal inserts……………………………………... 151
`
`
`4. SUMMARY……………………………………………………………………….…. 155
`
`5. ZUSAMMENFASSUNG………………………………………………………….… 161
`
`6. BIBLIOGRAPHY………………………………………………………………….... 167
`
`LIST OF PUBLICATIONS FROM THIS WORK………………………………….... 189
`
`CURRICULUM VITAE…………………………………………………………….….. 191
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`
`1. Introduction
`
`
`
`The aim of this work was the development and characterization of in situ gelling nasal inserts,
`a new, bioadhesive, solid dosage form for the prolonged systemic drug delivery via the nasal
`route. In this chapter conventional and alternative mucosal routes for systemic drug delivery
`are compared (section 1.1) and a basic introduction to the anatomy and physiology of the
`human nose (section 1.2) and to nasal immunology (section 1.4.1) is given. Further on, the
`concept of bioadhesion will be introduced (section 1.3) as a major approach to increase the
`nasal residence time of drug delivery systems. The current state of research concerning nasal
`drug delivery systems and nasal immunization approaches (sections 1.5 and 1.4.2) is
`presented. Finally, the objectives of this work are laid out.
`
`
`1.1. Transmucosal routes of drug delivery
`
`Drugs for systemic medication are administered traditionally and routinely by oral and by
`parenteral routes. Although generally convenient, both routes have a number of
`disadvantages, especially for the delivery of peptides and proteins, a class of drugs that has
`been rapidly emerging over the last decades (Zhou and Li Wan Po, 1991a). Oral
`administration results in the exposure of the drug to the harsh environment of the
`gastrointestinal tract and thus to potential chemical and enzymatic degradation (Langguth et
`al., 1997). After gastrointestinal absorption the drug has to pass the liver, where, dependent on
`the nature of the drug, extensive first pass metabolism can take place with subsequent rapid
`clearance from the blood stream (Lalka et al., 1993; Taki et al., 1998). Low permeability
`across the gastrointestinal mucosa is also often encountered for macromolecular drugs
`(Yamamoto et al., 2001; Pauletti et al., 1997). Parenteral administration avoids drug
`degradation in the gastrointestinal tract and hepatic first pass clearance but due to pain or
`discomfort during injection, patient compliance is poor, particularly if multiple daily
`injections are required as e.g. in the insulin therapy (Hinchcliffe and Illum, 1999). Also
`injection related side effects like tissue necrosis and thrombophlebitis lead to low patient
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`Introduction
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`acceptability (Zhou, 1994). In addition, administration by injection requires trained personnel
`which adds to the relatively high costs of parenteral medication.
`
`
`
`Figure 1. 1 Various potential mucosal pathways for systemic delivery of therapeutic
`agents, which bypass the hepatic first pass clearance associated with oral
`administration. The venous drainage system involved in the systemic delivery
`of therapeutic agents following the transmucosal permeation is illustrated
`(Zhou and Li Wan Po, 1991b).
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`Introduction
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`Several mucosal routes have been investigated over the last decades as alternatives to oral and
`parenteral drug administration, including nasal, buccal, rectal, ocular, pulmonary, and vaginal
`mucosa (Banga and Chien, 1988; Zhou and Li Wan Po, 1991b). Their advantages are the easy
`accessibility and circumvention of the hepatic first pass metabolism (Figure 1. 1). Mucosal
`bioavailability can vary between almost 100% for low molecular weight hydrophobic drugs
`(Striebel et al., 1993; Hussain et al., 1980) and below 1% for polar macromolecules (Zhou
`and Li Wan Po, 1991b; Illum, 2003) depending on the nature of the delivered drug. In the
`following, a short overview over the different alternative mucosal drug delivery routes is
`given.
`
`
`
`1.1.1. Nasal drug delivery
`
`The nasal route of administration, which is in the focus of this work, has received a great deal
`of attention in recent years as a convenient and reliable method not only for local but also for
`systemic administration of drugs (Schipper et al., 1991; Sakar, 1992; Merkus and Verhoef,
`1994; Kublik and Vidgren, 1998; Marttin et al., 1998; Davis, 1999; Hinchcliffe and Illum,
`1999; Martini et al., 2000; Chow et al., 2001; Illum, 2003). The nasal cavity offers a number
`of unique advantages such as easy accessibility, good permeability especially for lipophilic,
`low molecular weight drugs, avoidance of harsh environmental conditions and hepatic first
`pass metabolism, potential direct delivery to the brain, and direct contact for vaccines with
`lymphatic tissue and action as inducer as well as effector of the mucosal immune system (see
`section 1.2.4). The nasal epithelium is well suited for the transmucosal drug delivery although
`it is less permeable for hydrophilic and high molecular weight drugs (see section 1.1.7).
`Ciliary movement and the resulting clearance of the delivered drug / dosage form towards the
`throat are challenges when developing a prolonged release dosage form (see sections 1.2.2
`and 1.2.4). Also a considerable enzyme activity, though lower than in the gastrointestinal
`tract, must be considered. Nevertheless, a number of approaches have been used to overcome
`these limitations such as the use of bioadhesive formulations to increase the nasal residence
`time of dosage forms (Morimoto et al., 1991; Soane et al., 2001), addition of absorption
`enhancers to increase the membrane permeability (De Ponti, 1991; Merkus et al., 1993; Illum,
`1999, Natsume et al., 1999), and the use of protease / peptidase inhibitors to avoid enzymatic
`degradation of peptide and protein drugs in the nasal cavity (Morimoto et al., 1995; Dondeti
`et al., 1996). Several nasal dosage forms are under investigation including solutions (drops or
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`sprays), gels, suspensions and emulsions, liposomal preparations, powders and microspheres,
`as well as inserts (see section 1.5).
`
`
`
`1.1.2. Buccal drug delivery
`
`The oral cavity is lined by a stratified squamous epithelium. The epithelium has a cornified
`surface in regions subject to mechanical forces during mastication, which resembles that of
`the upper epidermis in the skin. Non-keratinized epithelium occupies approximately 60% of
`the total oral cavity including the buccal, lingual, and sublingual mucosa (Chien, 1995;
`Hoogstraate and Wertz, 1998) and is of interest for systemic drug delivery. Although non-
`keratinized, the buccal mucosa contains intercellular lipids which are responsible for its
`physical barrier properties (Hoogstraate and Wertz, 1998; Shojaei, 1998), resulting in poor
`permeability for larger drugs, especially for peptides and proteins (Junginger et al., 1999;
`Veuillez et al., 2001). Transfer of peptides with molecular weights above 500 - 1000 Da
`through buccal mucosa would require use of an absorption enhancer (Merkle et al., 1992).
`Another limitation in buccal drug delivery is the mucosal enzyme activity, especially of
`proteases (Bird et al., 2001; Veuillez et al., 2001; Walzer et al., 2002). The reduced retention
`of the dosage form at the buccal surface due to constant washing with saliva can be overcome
`by the use of bioadhesive formulations (Shojaei, 1998; Veuillez et al., 2001; Langoth et al.,
`2003). The influence of food intake and mastication on the residence time of bioadhesive
`buccal formulations is so far not clear. Thiolated polymers can be used simultaneously as
`bioadhesive carrier and protease inhibitors (Langoth et al., 2003). The sublingual epithelium
`is more permeable than the buccal one but more handicapped by the saliva washing and
`constant mobility (Shojaei, 1998). It is therefore more suitable for immediate release
`products.
`
`Dosage forms for buccal drug delivery include tablets, patches, films, lozenges, sprays,
`hydrogels, lollypops, chewing gums, powders, solutions (Hoogstraate and Wertz, 1998), a
`freeze-dried sublingual dosage form (Vaugelade et al., 2001), wafers (Kalra et al., 2001), and
`liposomal formulations (Veuillez et al., 2001).
`
`
`
`1.1.3. Ocular drug delivery
`
`Ocular delivery of drugs is typically for the treatment of ocular inflammation, corneal
`wounds, and glaucoma. In addition, this route has been investigated for the systemic delivery
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`of peptides and proteins. Already in 1931, ocular administration of insulin produced sustained
`lowering of the blood glucose level in proportion to the dose instilled (Christie and Hanzal,
`1931). However, today it is known that the majority of the systemic drug absorption after
`ocular instillation takes place across the nasal mucosa after drainage via the nasolachrymal
`duct (Lee et al., 2002). Some absorption occurs also from the conjunctival sac. Drug
`absorption via the cornea is relatively low due to the lipophilicity of the corneal epithelium,
`dilution of the drug in the tear fluid (reflex tearing and reflex blinking) and drug binding to
`proteins in tear fluid (Zhou and Li Wan Po, 1991b). In addition, the corneal and conjunctival
`tissues act also as enzymatic barrier, which contain e.g. proteases (Zhou and Li Wan Po,
`1991b). Therefore, the eye offers no additional advantage over the nose as systemic drug
`delivery site and is of higher interest only for drug administration for local (ophthalmic)
`therapy. However, also the local drug delivery is restricted by the dynamics of the lachrymal
`drainage system, which is the natural defense mechanism of the eye. This system introduces
`tear fluid to the eye and rapidly drains the fluid together with any instilled formulation from
`the precorneal area to the nasal cavity and throat. The high elimination rate results in short
`duration of contact of the drug with its absorption sites and consequently in a low local
`bioavailability. Increased ocular bioavailability can be achieved by the use of viscosity
`enhanced aqueous eye drops, suspensions, oily drops and unguents, mucoadhesive ocular
`delivery systems such as solutions and microparticle suspensions, in-situ gelling systems
`triggered by pH, temperature, or ions, colloidal delivery systems such as liposomes and
`nanoparticles, and ocular inserts (Le Bourlais et al., 1995). Ocular inserts can be divided into
`non-erodible (Chetoni et al., 1998; Kawakami et al., 2001) and erodible inserts. Erodible
`ocular inserts, which do not need to be removed mechanically from the eye, have been
`prepared by powder compression from poly(ethylene oxide) (Di Colo et al., 2001), from
`bioadhesive mixtures of poly(ethylene oxide) with chitosan hydrochloride (Di Colo et al.,
`2002), and from mixtures of Carbopol® 974P with drum dried waxy maize starch (Ceulemans
`et al., 2001; Weyenberg et al., 2003). Also absorbable gelatin sponge (Gelfoam®) soaked with
`an organic drug solution and subsequent solvent removal has been used as erodible ocular
`insert with improved bioavailability compared to eye drops and gels (Simomara et al., 1998).
`Finally, ocular inserts have also been prepared by freeze-drying aqueous solutions of water
`soluble polymers such as HPMC resulting in a sponge-like structure (Diestelhorst et al., 1999;
`Lux et al., 2003).
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`Introduction
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`1.1.4. Pulmonary drug delivery
`
`Pulmonary drug delivery has traditionally been used for the systemic administration of drugs
`such as anesthetic gases and nicotine (tobacco smoke). Direct delivery of drugs to the lung by
`inhalation for the local treatment of respiratory diseases grew rapidly in the second half of the
`20th century as a result of the availability of effective asthma drugs in convenient, portable
`devices (Gonda, 2000). The lung offers a number of advantages which render it also a suitable
`organ for systemic drug delivery: a large surface area of about 150 m2 and an extremely well
`vascularized, thin epithelium. Thus, various drugs including peptides and proteins (e.g.
`insulin, human growth hormone, luteinizing hormone releasing hormone analogue, glucagon,
`calcitonin) have efficiently been delivered via the lung (Qiu et al., 1997; Adjei and Gupta,
`1998; Edwards et al., 1998). A number of technologies for the delivery of drug formulations
`have been developed (Martini et al., 2000): (i) pressurized metered dose inhalers using
`propellants to deliver micronized drug suspensions (Autohaler®, Spacehaler®), (ii) dry powder
`inhalers which dispense micronized drug particles with / without carrier (lactose) by
`inhalation activation (Spinhaler®, Rotohaler®, Diskhaler®), and (iii) nebulizers and aqueous
`mist inhalers which aerosolize drug solutions using compressed air or ultrasound (AERx®,
`Respimat®). Although the pulmonary route of administration is very promising and the
`available delivery technologies are highly sophisticated, systemic drug delivery via the lung is
`still a challenging area of research. A key issue is the achievement of high delivery efficiency
`to the alveolar region. However, this is handicapped by the 90° bend in the oropharynx and
`the concomitant branching and narrowing of the bronchial tree (Malcolmson and Embleton,
`1998). The particle size should be in the aerodynamic diameter window of 0.5 - 5 µm, ideally
`2 - 3 µm, for deep lung delivery to avoid loss of delivered particles by impaction onto the
`mucus lined epithelia. The aerodynamic diameter relates the geometric particle diameter and
`the particle mass density. Thus, large porous particles are effective means for drug delivery to
`the alveolar region (Edwards et al., 1997; Vanbever et al., 1999; Crowder et al., 2002). Even
`optimized aerosol particles can be deposited in mouth and throat by inertia when delivered
`with too high a velocity (Edwards et al., 1998). In addition, the high humidity in the airways
`furthers particle agglomeration, thus decreasing the delivery efficiency due to hygroscopic
`growth (Malcolmson and Embleton, 1998; Crowder et al., 2002). Once in the lung, the
`particles must release the therapeutic substance at a desired rate and, in some case, escape the
`lung’s natural cleaning mechanisms (mucociliary transport in the conducting airways and
`phagocytosis by macrophages in the alveoli) until their therapeutic payload has been delivered
`(Kim and Folinsbee, 1997). Prolonged drug action after pulmonary delivery is another
`
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`challenge in pulmonary drug delivery and is approached by polymeric particle formulations
`(Kawashima et al., 1999; Zhang et al., 2001), mucoadhesive formulations (Takeuchi et al.,
`2001), and protein crystal formulations (Tam et al., 2001). However, in that case
`accumulation of polymeric material in the alveoli has to be taken into consideration as well as
`the possible delivery related development of fibrosis. Finally, the lung contains high levels of
`hydrolytic and other enzymes, which can become significant absorption barriers to drugs,
`although the metabolic activity of the lung is much lower than in the gastrointestinal tract.
`Numerous endoproteases and exoproteases were identified in lung tissue and in the bronchial
`lavage fluid (Adjei, 1997).
`
`
`
`1.1.5. Rectal drug delivery
`
`The lower digestive tract is less harmful to administered drugs than the stomach and the small
`intestine due to the lower enzymatic activity and neutral pH. Also the rectal route of drug
`administration is safe and convenient. In several countries it is generally accepted, especially
`for infants (Lejus et al., 1997; Jensen and Matsson, 2002), although the acceptance can be low
`in other states, particularly among adults. This may be overcome by the use of colon-specific
`drug targeting via the peroral route, which is under intensive investigation (Sinha and Kumria,
`2001; Raghavan et al., 2002) but not within the scope of this work. The adult’s lower intestine
`has also been shown to be relatively impermeable for macromolecules such as high molecular
`weight protein drugs and heparin (Warshaw et al., 1977; Zhou and Li Wan Po, 1991b;
`Lohikangas et al., 1994). Also a considerable protease activity still exists in the rectum and is
`still enhanced by the presence of bacterial flora (Lewin et al., 1986; Hacker et al., 1991; Zhou
`and Li Wan Po, 1991b). Additionally, the circumvention of the hepatic first pass metabolism
`by rectal administration is only partial and depends on the positioning and / or spreading of
`the drug formulation (de Boer and Breimer, 1997; Kurosawa et al., 1998).
`
`Traditional rectal dosage forms are suppositories, unguents and cremes, as well as enemas.
`More recent studies have evaluated thermogelling dosage forms (Miyazaki et al., 1998), gels
`(de Leede et al., 1986), osmotic mini pumps (Teunissen et al., 1985), and hard gelatin
`capsules (Eerikainen et al., 1996) as rectal drug delivery systems. Strategies to improve the
`rectal bioavailability of peptide and protein drugs include the use of absorption enhancers, the
`use of protease inhibitors and structural modifications of peptide and protein drugs
`(Yamamoto and Muranishi, 1997).
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`Introduction
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`1.1.6. Vaginal drug delivery
`
`It has been known for decades that a number of therapeutic agents, such as steroids, can be
`effectively absorbed through the vaginal mucosa (Ho et al., 1976; Alvarez et al., 1983).
`Traditionally, the vagina has been used for the delivery of locally acting drugs such as
`antibacterial, antifungal, antiprotozoal, antiviral, labor-inducing, and spermicidal agents,
`prostaglandins, and steroids (Vermani and Garg, 2000). The large surface area, rich blood
`supply and permeability to a wide range of compounds including peptides and proteins make
`the vagina also attractive for systemic drug administration (Benziger and Edelson, 1983;
`Honkanen et al., 2002; Valenta et al., 2002). The vaginal route has also the potential for
`uterine targeting of active agents such as progesterone and danazol (Bulletti et al., 1997;
`Cicinelli et al., 1998). Commonly used dosage forms are creams, gels, tablets, capsules,
`pessaries, foams, films, tampons, vaginal rings, and douches (Vermani and Garg, 2000). The
`vagina as drug delivery site has a number of unique features which have to be considered
`during the development of dosage forms. The vaginal pH of usually 4 - 5 is maintained by
`lactobacilli which convert glycogen into lactic acid. However, it changes with age, stage of
`menstrual cycle, infections, and sexual arousal (Vermani and Garg, 2000). The variation in
`vaginal pH and secretions may affect the absorption of pH-sensitive and / or solubility-
`dependent therapeutic agents (Chien, 1995). The vaginal microflora is also influenced by a
`number of factors (glycogen content of epithelial cells, pH, hormone levels, birth control
`method etc.) and can potentially contribute to enzymatic drug degradation in addition to the
`membrane-bound enzymes of the vaginal mucosa (Chien, 1995; Vermani and Garg, 2000).
`The changes in the hormone levels during the menstrual cycle vary also the enzyme activity
`of the mucosa as well as the thickness of the epithelial layer and width of the intercellular
`channels (Vermani and Garg, 2000). Limitations of systemic vaginal drug delivery next to the
`physiological barriers are also the gender specificity and the relatively low convenience.
`
`
`
`1.1.7. Comparison of transmucosal drug delivery routes
`
`With nasal, buccal, pulmonary, ocular, rectal, and vaginal mucosa as potential drug delivery
`sites, it is hard to identify the most suitable for clinical use. Only few studies were conducted
`to directly evaluate the different membrane permeabilities between these mucosal sites.
`Rojanaskul et al. (1992) measured the electrical membrane resistance and the flux of the
`hydrophilic probe 6-carboxyfuorescein at various mucosal sites and found a good correlation
`between these two parameters (Table 1. 1). The data indicates that nasal and pulmonary
`
`
`
`8
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`Introduction
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`
`epithelia are equally or only slightly less permeable than that of the intestine. The high
`permeability values of the respiratory tissue are a result of the presence of numerous aqueous
`pores through which water-soluble molecules can diffuse. Both large and small pores were
`reported in the nasal and pulmonary epithelium. The aqueous pores in the nasal epithelium,
`particularly those of small size (0.4 - 0.8 nm), were found to be more abundant than those
`observed in the jejunum (0.7 - 1.6 nm) (Hayashi et al., 1985). In the pulmonary epithelium,
`pores of 0.6 - 1.0 nm size and large pores of ≥ 8 nm were reported (Taylor and Gaar, 1970).
`
`Table 1. 1 Membrane electrical resistance and flux of 6-carboxyfluorescein of various
`mucosal sites (mean ± SD, n = 6)(Rojanaskul et al., 1992).
`
`Membrane
`tissue
`
`Membrane electrical resistance,
`Ω·cm2
`
`Steady state flux of 6-
`carboxyfluorescein, 106 µg/cm2·h
`
`Skin
`
`Buccal
`
`Corneal
`
`Rectal
`
`Vaginal
`
`Tracheal
`
`Colonic
`
`Bronchial
`
`Ileal
`
`Nasal
`
`Jejunal
`
`Duodenal
`
`
`
`9703 ± 175
`
`1803 ± 175
`
`1012 ± 106
`
`406 ± 70
`
`372 ± 85
`
`291 ± 65
`
`288 ± 72
`
`266 ± 97
`
`266 ± 95
`
`261 ± 55
`
` 224 ± 104
`
`211 ± 91
`
`9
`
` 0.5 ± 0.4
`
` 3.0 ± 1.3
`
` 5.1 ± 1.7
`
` 9.9 ± 2.3
`
`12.4 ± 4.1
`
`14.2 ± 5.4
`
`16.3 ± 6.8
`
`16.7 ± 4.5
`
`19.6 ± 3.9
`
`16.8 ± 1.8
`
`21.1 ± 6.2
`
`21.0 ± 3.9
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`

`
`Introduction
`1.
`___________________________________________________________________________
`
`The nasal epithelium is leakier for peptide molecules than intestinal epithelia when using
`metabolically stable peptides as permeability tracers (McMartin et al., 1987). Opposite to
`other reports with mannitol and progesterone (Corbo et al., 1990) and 6-carboxyfluorescein
`(Rojanaskul et al., 1992), Aungst et al. (1988) demonstrated that nasal, buccal, and sublingual
`insulin administration were less efficient than administration via rectal mucosa. This finding
`suggests that also other factors like enzyme activity and absorptive surface area may play a
`role in determining the overall bioavailability. The large absorptive surface of the lung would
`make the pulmonary mucosa a very effective route of administration. This was also
`demonstrated by an absorption study in rats with different water-soluble compounds (Phenol
`Red, Trypan Blue, fluorescein isothiocyanate dextran molecular weight 4400 and 9100)
`which revealed bioavailabilities after mucosal administration of the order lung > small
`intestine > nasal cavity > large intestine > buccal cavity (Yamamoto et al., 2001). In the same
`study the pharmacological availability of [ASU1.7]-eel calcitonin gave the order lung > nasal
`cavity > small intestine = large intestine ≥ buccal cavity which was attributed to the higher
`protease content in the small intestine compared to the nasal cavity. The proteolytic activity in
`different animals is relatively high in the rectal and ileal mucosa and comparatively low in the
`buccal, nasal, and vaginal mucosal tissue (Table 1. 2) (Zhou and Li Wan Po, 1991b).
`
`Due to the clear advantages of accessibility, patient convenience, and permeability, nasal and
`pulmonary drug delivery are the most promising transmucosal delivery routes. The quantity
`of drug that can be delivered to the lung may be more limiting than that given nasally