Journal of Controlled Release 87 (2003) 187–198
`
`www.elsevier.com/locate /jconrel
`
`N asal drug delivery—possibilities, problems and solutions
`a,b ,*
`Lisbeth Illum
`aWest Pharmaceutical Services, Drug Delivery and Clinical Research Centre Ltd., Albert Einstein Centre,
`Nottingham Science and Technology Park, Nottingham,UK
`bID-entity,19 Cavendish Crescent North, The Park, Nottingham NG71BA,UK
`
`Abstract
`
`This paper discusses the problems associated with nasal drug delivery and how it is possible, sometimes by means of quite
`simple concepts, to improve transport across the nasal membrane. In this way it is feasible to deliver efficiently challenging
`drugs such as small polar molecules, peptides and proteins and even the large proteins and polysaccharides used in vaccines
`or DNA plasmids exploited for DNA vaccines. The transport of drugs from the nasal cavity directly to the brain is also
`described and examples of studies in man, where this has been shown to be feasible, are discussed. Recent results from
`Phase I/II studies in man with a novel nasal chitosan vaccine delivery system are also described. Finally, the author’s
`thoughts about the future for nasal drug delivery are also depicted.
` 2002 Published by Elsevier Science B.V.
`
`1 . Introduction
`
`the nasal route of delivery has
`Conventionally,
`been used for delivery of drugs for treatment of local
`diseases such as nasal allergy, nasal congestion and
`nasal infections. Recent years have shown that the
`nasal route can be exploited for the systemic delivery
`of drugs such as small molecular weight polar drugs,
`peptides and proteins that are not easily administered
`via other routes than by injection, or where a rapid
`onset of action is required [1]. Marketed products
`include a range of anti-migraine drugs such as
`sumatriptan from GlaxoSmithKline,
`zolmitriptan
`from AstraZeneca, ergotamine from Novartis and
`butorphanol from BristolMyersSquibb, as well as a
`range of peptides, such as calcitonin marketed by
`Novartis, desmopressin from Ferring and buserelin
`
`*Tel.: 144-115-9481-866; fax: 144-115-9799-031.
`E-mail address: lisbeth.illum@ccinternet.co.uk (L. Illum).
`
`from Aventis (Table 1). A wide range of nasal
`products is in development, mostly aimed for ex-
`ploiting the advantage of a rapid onset of action
`when administered via this route, for example for the
`treatment of pain, nasal morphine and ketamine and
`for
`the treatment of erectile dysfunction, nasal
`apomorphine. Lately the use of the nasal route for
`delivery of vaccines, especially against respiratory
`infections such as influenza, has also attracted inter-
`est from the pharmaceutical companies specialising
`in vaccine delivery. This is due to the possibility of
`obtaining not only a systemic but also a local
`immune response. Hence, the first nasal influenza
`product from the Swiss company, Berna Biotech
`reached the European market in 2001 (but is now
`withdrawn due to potential toxicological problems)
`and a second product from Aviron is due to be
`launced in 2003 [2]. The present paper discusses the
`problems associated with nasal delivery of drugs and
`how barriers to the nasal absorption of especially
`
`0168-3659/02/$ – see front matter  2002 Published by Elsevier Science B.V.
`doi:10.1016/S0168-3659(02)00363-2
`
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`Table 1
`Nasal delivery of peptides and proteins
`• Nasal salmon calcitonin
`• Marketed by Novartis
`• Novel nasal formulations under development by other pharmaceutical companies
`• Nasal desmopressin
`• Marketed by Ferring and partners
`• Nasal buserelin
`• Marketed by Aventis
`• Nasal nafarelin
`• Marketed by Searle
`• Nasal PTH, nasal leuprolide, nasal insulin, nasal interferon, etc.
`• In clinical trials
`
`challenging drugs can be overcome. It also highlights
`the possibilities for achieving novel targets (Brain,
`CSF) using this route of delivery.
`
`2 . The nasal cavity
`
`The nasal cavity has an important protective
`function in that it filters, warms and humidifies the
`inhaled air before it reaches the lower airways. Any
`inhaled particles or microorganisms are trapped by
`the hairs in the nasal vestibule or by the mucus layer
`covering the respiratory area of the nasal cavity. Due
`to the mucociliary clearance mechanism, the mucus
`layer will gradually carry such particulates to the
`back of the throat, down the oesophagus and further
`into the gastrointestinal tract. Furthermore, the nasal
`mucosa has a metabolic capacity that will help
`convert endogenous materials into compounds that
`are more easily eliminated.
`A midline septum divides the human nasal cavity
`into two non-connected parts. Each part consists of
`three regions: Firstly, the vestibule consisting of the
`region just inside the nostrils with an area of about
`2
`0.6 cm . Secondly, the olfactory region, which in
`man is situated in the roof of the nasal cavity and
`only covers about 10% of the total nasal area of 150
`2cm as opposed to for example in the dog where the
`area constitute 77% of the total nasal cavity, and
`thirdly the respiratory region which constitute the
`remaining region. The respiratory region contains the
`three nasal turbinates, the superior, the middle and
`the inferior which project from the lateral wall of
`each half of the nasal cavity. The presence of these
`turbinates creates a turbulent airflow through the
`
`nasal passages which ensures a better contact be-
`tween the inhaled air and the mucosal surface.
`Similar, more or less complex turbinate structures
`are present in all animal models normally used for
`nasal delivery studies.
`The nasal vestibule is covered with stratified
`squamous epithelium which gradually changes poste-
`riorly into a pseudostratified columnar epithelium
`that covers the respiratory epithelium. The respirato-
`ry epithelial cells are covered by microvilli and the
`major part of these cells is also covered with cilia.
`These cilia, which are long (4–6 mm) thin projec-
`tions, are mobile and beat with a frequency of 1000
`strokes per min. The beat of each cilium consists of a
`rapid forward movement, where the cilium is
`stretched and the tip of the cilium reaches into the
`mucus layer and carries this forward followed by a
`slow return beat, where the cilium is bent and moves
`in the sol layer that lies beneath the mucus layer. In
`this way the mucus layer is propelled in a direction
`from the anterior towards the posterior part of the
`nasal cavity. The mucus flow rate is in the order of 5
`mm per min and hence the mucus layer is renewed
`every 15–20 min.
`
`3 . Barriers to nasal absorption
`
`Lipophilic drugs are generally well absorbed from
`the nasal cavity with the pharmacokinetic profiles
`often identical to those obtained after an intravenous
`injection and bioavailabilities approaching 100%. A
`good examples of this is the nasal administration of
`fentanyl where the T
`for both intravenous and
`max
`nasal administration have been shown to be very
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`max
`
`rapid (7 min or less) and the bioavailability for nasal
`administration was near 80% [3]. However, despite
`the large surface area of the nasal cavity and the
`extensive blood supply, the permeability of the nasal
`mucosa is normally low for polar molecules,
`to
`include low molecular weight drugs and especially
`large molecular weight peptides and proteins. For
`small polar drugs the bioavailabilities are generally
`in the region of 10% and for peptides such as
`calcitonin and insulin normally not above 1%. It is
`interesting to note that the nasal sumatriptan product
`on the market has a pharmacokinetic profile not
`dissimilar to that obtained after oral administration
`and a bioavailability of 15.8% as compared to 14.3%
`after oral administration [4]. It is evident from the
`published results that only a minor part of
`the
`absorption is due to absorption from the nasal cavity
`(small peak at 30 min) and that a C
`obtained after
`2 h is due to oral absorption.
`limiting the nasal
`The most
`important
`factor
`absorption of polar drugs and especially large molec-
`ular weight polar drugs such as peptides and proteins
`is the low membrane permeability. Drugs can cross
`the epithelial cell membrane either by the transcellu-
`lar route, exploiting simple concentration gradients,
`receptor mediated transport or vesicular transport
`mechanisms or by the paracellular route through the
`tight junctions between the cells. Polar drugs with
`molecular weights below 1000 Da will generally
`pass the membrane using the latter route, since,
`although tight junctions are dynamic structures and
`can open and close to a certain degree, when needed,
`the mean size of the channels is in the order of less
`˚
`than 10 A and the transport of larger molecules is
`considerably more limited [5,6]. Larger peptides and
`proteins have been shown to be able to pass the nasal
`membrane using an endocytotic transport process but
`only in low amounts [7,8].
`Another factor of importance for low membrane
`transport is the general rapid clearance of the ad-
`ministered formulation from the nasal cavity due to
`the mucociliary clearance mechanism. This is espe-
`cially the case for drugs that are not easily absorbed
`across the nasal membrane. It has been shown that
`for both liquid and powder formulations, that are not
`mucoadhesive, the half life of clearance is in the
`order of 15–20 min [9,10]. It has further been
`suggested that the deposition of a formulation in the
`
`anterior part of the nasal cavity can decrease clear-
`ance and promote absorption as compared to deposi-
`tion further back in the nasal cavity [11]. Most nasal
`sprays of various makes have been shown to deliver
`the formulation to a limited area in the anterior part
`of the nasal cavity as opposed to nasal drops which
`will be delivered to a larger area further back in the
`nasal cavity.
`The nasal absorption of such polar drugs can be
`greatly improved if administered in combination with
`absorption promoting agents. Agents described in the
`literature for nasal drug delivery have included
`surfactants such as laureth-9, bile salts and bile salt
`derivatives such as sodium taurodihydrofusidate,
`fatty acids or fatty acid derivatives, phospholipids as
`well as various cyclodextrins [1]. These enhancer
`systems work by a variety of mechanisms but
`generally change the permeability of the epithelial
`cell
`layer by modifying the phospholipid bilayer,
`leaching out protein from the membrane or even
`stripping off the outer layer of the mucosa. Some of
`these enhancers also have an effect on the tight
`junctions and/or work as enzymatic inhibitors. For
`such enhancing agents greatly enhanced bioa-
`vailabilities have been obtained, even for
`larger
`peptides such as insulin at least in animal models.
`Less sucess has been achieved in Phase 1 clinical
`trials, very often due to a lesser effect in humans or
`to the irritancy of the enhancer material in the nasal
`cavity. In animal studies it has been shown for a
`range of enhancing agent
`that
`there is a direct
`correlation between absorption enhancing effect
`(bioavailability) obtained and the damage caused to
`the nasal membrane [1]. This is particularly true for
`surfactant materials and bile salts. For other en-
`hancers, such as some of the cyclodextrins, chitosan
`and selected phospholipids the absorption enhancing
`effect outweighs any damage caused to the mucosa.
`Hence, it is of great importance that one considers
`carefully the choice of an absorption enhancer for a
`nasally delivered drug that is not readily absorbed
`especially in terms of potential nasal and systemic
`toxicity.
`Another contributing (but normally considered
`less important) factor to the low transport of espe-
`cially peptides and proteins across the nasal mem-
`brane is the possibility of an enzymatic degradation
`of the molecule either within the lumen of the nasal
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`cavity or during passage across the epithelial barrier.
`These sites both contain exopeptidases such as
`mono- and diaminopeptidases that can cleave pep-
`tides at their N and C termini and endopeptidases
`such as serine and cysteine, that can attack internal
`peptide bonds [12]. A range of studies has been
`carried out in vitro using tissue homogenates or nasal
`wash or in vivo in animal models to assess the
`possible effect of such enzymes on the stability of
`peptides [13–15]. However, it is often difficult to
`truly evaluate the relevance of the experimental set
`up to the real in vivo situation in man. Very often the
`exposure of the peptide to the enzyme has been
`overestimated and for some peptides degradation
`half-lives of less than 30 min have been quoted.
`
`4 . Chitosan
`
`In designing effective delivery systems for a range
`of challenging molecules especially biopharmaceuti-
`cals, we have tried to take into account the factors
`that can effect nasal absorption. Absorption has been
`improved by using a number of strategies taking into
`account the drug, the disease and the destination. We
`have concentrated on overcoming two of the main
`barriers to effective absorption, namely transport
`across the epithelial membrane and the rapid muco-
`ciliary clearance of the formulation. We have focused
`upon a strategy employing the use of bioadhesive
`nasal delivery systems that provide the prolonged
`contact between the drug formulation and the absorp-
`tive sites in the nasal cavity by delaying the muco-
`ciliary clearance of the formulation. Such bioadhe-
`sive systems can be in the form of powders as well
`as liquids or liquid gelling systems. The powders can
`be administered as freeze dried or spray dried
`particles or microspheres. For such systems we have
`found starch and chitosan to be preferred materials in
`terms of their efficiency. Most recently we have
`focused our work on the use of the bioadhesive
`polysaccharide chitosan and the development of a
`range of delivery systems based on this material [1].
`Chitosan is a positively charged linear polysac-
`charide that
`is bioadhesive and able to interact
`strongly with the nasal epithelial cells and the
`overlaying mucus layer thereby providing a longer
`contact
`time for drug transport across the nasal
`
`Fig. 1. Chitin and chitosan.
`
`membrane, before the formulation is cleared by the
`mucociliary clearance mechanism [1,10,16]. In addi-
`tion, chitosan has been shown (in Caco-2 cell culture
`studies) to increase the paracellular transport of polar
`drugs by transiently opening the tight
`junctions
`between the epithelial cells [17,18]. Chitosan is
`produced from chitin present in shells of crustaceans
`by a process of deacetylation and is available in a
`range of molecular weights and degrees of deacetyla-
`tion. The structure of chitosan is shown in Fig. 1.
`The type of chitosan most often employed for nasal
`delivery is a chitosan glutamate salt of a mean
`molecular weight around 250 kDa and a degree of
`deacetylation of more then 80%. This chitosan salt is
`soluble in water up to a pH of about 6.5.
`
`5 . Nasal delivery of polar drugs
`
`Various pre-clinical and clinical studies have been
`carried out
`in animal models and in human vol-
`unteers and patients for the development of therapeu-
`tically relevant nasal formulations of small polar
`drugs and a range of peptides and proteins using the
`chitosan nasal delivery system. Morphine is a good
`example, since for the management of breakthrough
`pain it
`is important
`to obtain a pharmacokinetic
`profile where an early peak plasma level is achieved
`and thereby a rapid onset of action is provided. This
`is not achieved at present. Breakthrough pain is
`generally treated with oral morphine solution or
`similar drugs where the plasma peak level is not
`achieved before 30–45 min after administration. The
`morphine opioid is relatively polar (log P50.89) and
`when administered nasally in a simple formulation to
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`191
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`human volunteers the pharmacokinetic profile resem-
`bles that following an oral administration with a T
`max
`about 40 min [19]. Only low amounts are absorbed
`nasally of the order of 5–10%.
`However, when morphine is administered in a
`simple chitosan solution formulation a five to six-
`fold increase in bioavailability to about 60% is
`achieved with a T
`of 15 min or less [20]. The
`max
`shape of the plasma curve has been found to be
`similar to that obtained for the intravenous adminis-
`tration of morphine (Fig. 2). Furthermore, the meta-
`bolic profiles obtained after intravenous and nasal
`administration of the respective formulations were
`very similar with comparable ratios between the
`plasma
`levels
`of morphine-3-glucuronide
`and
`morphine-6-glucuronide and similar low levels of
`both metabolites as compared to the five times higher
`levels of both after oral administration. It was also
`found that the nasal formulation was well tolerated
`with minimal side effects of less than 30% of total
`maximal scores. The effect of the nasal chitosan–
`morphine formulation on the management of break-
`through pain has been investigated in a pilot study in
`14 cancer patients. This demonstrated that within 5
`
`min the patients experienced a significant decrease in
`pain intensity and an associated increase in pain
`relief [21]. The chitosan–morphine nasal product is
`now in Phase II clinical trials both in the USA and in
`the UK and is expected to reach the market within
`the next 2 years.
`Apart from the small molecular weight drugs, the
`chitosan delivery system, whether in the form of a
`solution or a powder, has also been shown to be very
`effective in delivering peptides such as leuprolide
`(1300 Da), salmon calcitonin (S-CT) (3500 Da) and
`parathyroid hormone (PTH) (4000 Da) across the
`nasal membrane. Nasal bioavailabilities of around
`20% or more have been obtained in clinical trials for
`these drugs. Generally,
`it has been shown that
`chitosan powder formulations, whether in the form
`of microspheres or powders, can in many instances
`be able to provide a better absorption promoting
`effect than chitosan solutions. Hence, for the LHRH
`analogue, goserelin it was found in the sheep model
`that a chitosan microsphere formulation was able to
`provide bioavailabilities in the order of 40% relative
`to an intravenous injection [22]. For some drugs,
`such as PTH, a chitosan powder formulation is also
`
`Fig. 2. A comparison between the pharmacokinetic profile of morphine (10 mg) administered as a slow (30 min) infusion (A) and morphine
`administered nasally in a chitosan solution formulation (B).
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`the most appropriate formulation due to stability
`problems encountered with PTH solution formula-
`tions.
`
`6 . Nose to brain delivery
`
`Recent developments have highlighted the possi-
`bility of exploiting the nasal route for direct transport
`of drugs from nose to brain in man. Hence, Frey [23]
`declared that by nasally administering insulin-like
`growth factor (IGF-1) the drug could bypass the
`blood–brain barrier and reach the central nervous
`system (CNS) directly from the nasal cavity. Reports
`in the literature of studies in animal models and in
`man have shown this to be a distinct possibility with
`results showing the uptake of drugs into the cere-
`brospinal fluid and the brain tissue being dependent
`upon molecular weight and the lipophilicity [24–28].
`3
`In mice, it was shown recently that [ H]-dopamine
`reached the right olfactory bulb after nasal adminis-
`tration into the right nostril and that at 4 h the
`concentration in the bulb was 27 times higher than
`that in the left olfactory bulb [29]. Following in-
`travenous administration the uptake into the brain
`was low. The paper did not disclose the total
`
`quantity that actually reached the brain. However,
`according to previous studies in animal models it has
`been shown that the total amount appearing in the
`brain tissue seldom amount to more than nM quan-
`tities or a bioavailability of 0.01–0.1% [24].
`The routes by which nasally delivered drugs can
`reach the cerebro-spinal fluid (CSF), which sur-
`rounds the brain and the actual brain tissue,
`is
`depicted in Fig. 3. The thickness of the individual
`arrows indicates the likelihood of drugs actually
`exploiting this route of transport. When administered
`nasally the drug formulation will normally be cleared
`rapidly from the nasal cavity into the gastrointestinal
`tract by the mucociliary clearance system. A quantity
`of the drug will (dependent on the lipophilicity and
`molecular weight) be absorbed across the nasal
`mucosa and reach the systemic circulation from
`where it will be eliminated via normal clearance
`mechanisms. The drug can also follow the systemic
`pathway to reach the brain by crossing the blood
`brain barrier but the use of this pathway is highly
`dependent on the properties of the drug. Of special
`interest is the transport of drug across the olfactory
`region in the nasal cavity directly into the brain
`tissue (e.g. olfactory bulb) or the CSF. Due to the
`normal replacement of the CSF (four to five times
`
`Fig. 3. Possible routes of transport between the nasal cavity and the brain and CSF.
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`193
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`daily), the drug will also gradually be eliminated
`from the CSF into the blood.
`The olfactory epithelium is situated between the
`nasal septum and the lateral wall of each side of the
`two nasal cavities and just below the cribriform plate
`of the ethmoid bone separating the nasal cavity from
`the cranial cavity. The olfactory epithelium is a
`modified form of respiratory epithelium in that it is a
`pseudostratified epithelium that, apart from the sup-
`porting epithelial cells with villi and basal cells, also
`contains olfactory receptor cells. The olfactory re-
`ceptor cells are bipolar neurones with a single
`dendritic process extending from the cell body to the
`free apical surface where it ends in a small knob
`carrying non-motile cilia. At
`the basal end the
`neuron ends in a fine non-myelated axon that joins
`with other axons into a bundle surrounded by glial
`cells (and CSF) and penetrates into the cranial cavity
`through small holes in the cribriform plate.
`In order for a drug to reach the CNS from the
`nasal cavity,
`it will have to cross the olfactory
`membrane and depending on the pathway used also
`the arachnoid membrane surrounding the arachnoid
`space containing the CSF. The drug can cross the
`olfactory pathway by one or a combination of
`pathways. Firstly, the drug can use a transcellular
`pathway, where the drug is transferred by receptor
`mediated endocytosis, fluid phase endocytosis of by
`passive diffusion. This pathway is especially suited
`for small lipophilic molecules or large molecules.
`Secondly, the drug can use the paracellular pathway
`by passing through the tight junctions or through
`open clefts in the membrane. This pathway is
`especially suited for smaller hydrophilic molecules.
`Thirdly,
`the drug can be transported through the
`olfactory neuron cells by intracellular axonal trans-
`port primarily to the olfactory bulb.
`In our own studies we have concentrated on the
`mechanisms and transport pathways in order
`to
`elucidate ways of improving the rate and quantity of
`drug reaching the brain. Hence, we have investigated
`the transport of a reasonable hydrophilic zwitterionic
`drug across the nasal membrane into the CNS using
`the rat model. The results have shown that the uptake
`of the drug into the olfactory lobe was significantly
`higher after nasal administration than after intraven-
`ous administration. The AUC for the olfactory lobe
`was six times larger after nasal administration as
`
`compared to intravenous administration for the first
`30 min, whereas the AUC for the plasma was 2.5
`times lower. This showed that the drug was trans-
`ported across the nasal membrane into the olfactory
`lobe. Whole body autoradiography of the rat at 1, 5,
`10 and 30 min after administration showed a distinct
`increase in radioactivity of the brain area indicating
`either an increasing brain tissue uptake or an increas-
`ing CSF uptake. The CSF concentration was not
`measured. Microautoradiography of
`the olfactory
`region of
`the rat showed the presence of drug
`molecules along the olfactory neuron bundles. This
`can either indicate transneural transport or transport
`via the CSF surrounding the bundles. However,
`considering that transneural transport of drugs is a
`slow process it
`is most
`likely that
`the drug had
`crossed the olfactory region by means of one of the
`other transport mechanisms and reached the CSF and
`the olfactory bulb.
`Evidence that nose to brain transport is also taking
`place in man is steadily accumulating in various
`reports and papers [25–27,30–34]. Table 2 gives an
`overview of some of the latest studies performed in
`man. The first group of studies mostly comprised an
`investigation of the pharmacodynamic effect on the
`CNS in terms of specific effects on the event-related
`potentials during the subject’s performance of an
`auditory (or similar) attention task (oddball
`task)
`comparing drug administration via nasal and in-
`travenous routes of delivery. As an example, Piet-
`rowsky [30] administered cholecystokinin-8 (CCK)
`to 20 healthy volunteers in a placebo controlled,
`double blind, cross-over study by the nasal and the
`intravenous route and recorded the auditory event-
`related potentials (AERP) during the volunteer’s
`performance of an oddball task. Plasma CCK con-
`centrations were similar after both routes of adminis-
`tration. Nasal administration of CCK markedly in-
`creased the P3 complex of the AERP, whereas this
`effect was not seen after intravenous administration.
`It was concluded that this effect was due to a direct,
`most likely extracellular pathway, between the olfac-
`tory region in the nasal cavity and the brain.
`The first attempt at radioisotopic assessment of the
`integrity of the nose to brain barrier in man was
`published by Okuyama [31]. A mixture of 99mTc-
`DTPA and hyaluronidase was sprayed onto the
`olfactory mucosa of anosmic patients and the cere-
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`Table 2
`Studies indicative of nose to brain drug transport in man
`• Functional evidence of facilitated transport to the brain was provided by changes in event related
`potential during performance of an oddball task
`• Arginin–vasopressin (n515) [43]
`• Cholecystokinin-8 (n520) [30]
`• Angiotensin II (n512) [32]
`• Insulin (n518) [44]
`• Adrenocorticotropin 4-10 (n554) [45]
`• Insulin (n512) [34]
`
`• Direct evidence of nose to brain uptake
`• 99mTc-DTPA–hyaluronidase [31]
`
`• Direct evidence of nose to CSF uptake
`• Insulin (n58) [26]
`• Apomorphine (n55) ? [25]
`• Melatonin/ hydroxycobalamin (n52) [46]
`
`bral radioactivity measured. A significant rise in
`cerebral
`radioactivity was observed 5 min after
`application of the radioisotope. More recent studies
`have not only studied the effect on brain potentials
`but have also compared specific drug concentrations
`in the CSF after nasal and intravenous administra-
`tion. Hence, in a pilot study in eight healthy vol-
`unteers Fehm et al. [26] reported a distinct accumu-
`lation of insulin in the CSF sampled from a spinal
`tap after a single nasal administration of 40 IU
`insulin. No rise was seen in serum levels. It is well
`known that without the addition of an absorption
`enhancer insulin does not easily cross the nasal
`membrane to enter the blood stream so it is unlikely
`that the insulin reached the brain via the blood–brain
`barrier.
`Recently, it was announced in a press release that
`a Phase 1 clinical study in human volunteers had
`shown that at 20 min after the nasal administration of
`apomorphine the concentration of the drug in the
`CSF was equivalent to 27–44% of the concentration
`found at the same time in the plasma, whereas after
`subcutaneous administration the CSF levels were
`equivalent to only 2.5–4.3% of the plasma levels
`[25]. The CSF was sampled by spinal tap. Although
`this study does indicate that a direct transport from
`nose to the CSF may have taken place the study
`lacks information on CSF levels after an intravenous
`injection of apomorphine to give an indication of
`apomorphine’s ability to cross the blood–brain bar-
`rier. Furthermore,
`the subcutaneous results were
`
`taken from the literature and injections were not
`performed in the same group of people.
`It is evident that in situations where it is necessary
`to target receptors in the brain, as for example for
`Parkinson’s disease, treatment of Alzheimer’s dis-
`ease or the treatment of pain, a specific delivery to
`the CNS would be beneficial. In such situations
`efforts should be given to the development of
`delivery systems capable of increasing the fraction of
`the drug that reaches the CNS after nasal delivery.
`However, in other situations, when a transport of
`nasally administered drugs to the brain may not be
`beneficial or even harmful
`to the patient,
`it
`is
`necessary to ensure that the transport of the drug to
`the blood stream is maximised. Very little effort has
`so far been directed to the possibility of enhancing or
`decreasing the transport to the brain via the nose by
`means of appropriate delivery systems. This is an
`area that warrants further investigation.
`
`7 . Nasal delivery of vaccines
`
`Many diseases, such as measles, pertussis, menin-
`gitis and influenza are associated with the entry of
`pathogenic microorganisms across the respiratory
`mucosal surfaces and are hence good candidates for
`nasal vaccines. The main reasons are given in Table
`3. It
`is well established that nasally administered
`vaccines, especially if based on attenuated live cells
`or adjuvanted by means of an immunostimulator or a
`
`AQUESTIVE EXHIBIT 1027 page 0008
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`L. Illum / Journal of Controlled Release 87 (2003) 187–198
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`195
`
`Table 3
`Main reasons for exploiting the nasal route for vaccine delivery
`• The nasal mucosa is the first site of contact with inhaled antigens
`• The nasal passages are rich in lymphoid tissue (Nasal Associated Lymphoid Tissue-NALT
`• NALT is known as Waldeyer’s ring in humans
`• Adenoid or nasopharyngeal tonsils
`• Bilateral lymphoid bands
`• Bilateral tubal and facial or palatine tonsils
`• Bilateral lingual tonsils
`• Creation of both mucosal (sIgA) and systemic (IgG) immune responses
`• Low cost, patient friendly, non-injectable, safe
`
`delivery system, can induce both mucosal and sys-
`temic (i.e. humoral and cell-mediated) immune-re-
`sponses. The nasal passages are rich in lymphoid
`tissues and the target site for nasally administered
`vaccines in man is considered to be nasal-associated
`lymphoid tissue (NALT) which is situated mainly in
`the pharynx as a ring of lymphoid tissue and named
`Waldeyer’s ring.
`A range of different nasal vaccine systems has
`been described in the literature either using live or
`attenuated whole cells, split cells, proteins or poly-
`saccharides and with and without various adjuvants
`and delivery systems [35–37]. Some of these sys-
`tems were shown to be efficient not only in mice but
`also in man [38]. It is interesting to note that Van
`Ginkel et al. [39] in a recent paper found that
`GM1-binding molecules like cholera toxin (CT) and
`cholera toxin-B subunit
`(CT-B)
`that are potent
`adjuvants, targeted the olfactory nerves/ epithelium
`after nasal administration and were transported in a
`retrograde manner to the olfactory bulbs. CT and
`CT-B promoted the uptake of vaccine proteins (such
`as tetanus toxoid (TT)) into the olfactory neurones
`whereas TT without the adjuvant did not penetrate
`into the CNS after nasal administration.
`The chitosan nasal delivery system has been tested
`with three different vaccines, namely for influenza,
`pertussis and diphtheria in various animal models
`and in man. It has been shown that chitosan sig-
`nificantly enhances the immune response obtained
`from influenza vaccine when given nasally to mice,
`with IgG levels similar
`to those obtained after
`parenteral application and significant IgA levels both
`in the nasal fluid and in the lungs. Lymphocytes
`secreting antibody specific for HA were recovered
`from nasal mucosa in all groups of animals. Recent-
`ly, a Phase 1 clinical trial of nasal chitosan influenza
`
`vaccine has shown promising results, with more than
`four fold increase in HI values relative to pre-dose
`HI values and HI values of 40 or higher indicative of
`protective levels of the antigen. Levels were similar
`for IM conventional
`influenza vaccine and nasal
`administration of the chitosan-influenza vaccine [2].
`¨
`Similarly,
`in studies in naıve guinea pigs it was
`shown that diphtheria vaccine (CRM197) adminis-
`tered nasally in a chitosan formulation provided
`significantly higher serum IgG titres than the