Advanced Drug Delivery Reviews, 8 (1992) 165-177 165 © 1992 Elsevier Science Publishers B.V. All rights reserved. 0169-409X/92/$05.00 ADR 00107 (D) Routes of Delivery: Case Studies (1) Nasal delivery of peptide drugs Peter Edman a'b and Erik Bj6rk a'b aKabi Pharmacia Therapeutics AB, Uppsala, Sweden, and bDepartrnent of Pharmaceutics, Uppsala University, BMC, Uppsala, Sweden (Received November 5, 1990) (Accepted May 6, 1991) Key words: Nasal delivery; Microsphere; Enhancer; Bioavailability; Animal model Contents Summary ......................................................................................................... 166 I. Introduction ............................................................................................ 166 II. Nasal physiology ...................................................................................... 166 II1. Some basic characteristics of existing nasal drug delivery systems ........................ 168 IV. Enhancer systems ..................................................................................... 169 V. New enhancer systems ............................................................................... 171 VI. Conclusion .............................................................................................. 174 References ........................................................................................................ 175 Abbreviations: STDHF, sodium tauro-24,25-dihydrofusidate; SVP, small volume parenterals; i.v., intravenous; DEAE, diethylaminoethyl; LPC, lysophosphatidylcholine; hGH, human growth hormone; CMC, critical micellar concentration; AUC, area under the curve; LHRH, luteinizing hormone-releasing hormone; IgA, immunoglobulin A. Correspondence: E. Bj6rk, Kabi Pharmacia Therapeutics AB, Rapsgatan 7, 751 82 Uppsala, Sweden, Fax: (46) (18) 154135.
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`166 P. EDMAN AND E. BJC)RK Summary This chapter summarises the problems associated with and the potential of nasal drug administration. The physiology and the anatomy of the nasal cavity are briefly discussed. Limitations of currently available nasal formulations are presented and solutions to the major problem, low bioavailability, are proposed. The biopharmaceutical properties and toxicity of both old and new enhancer systems are discussed. A dry particulate system, starch microspheres which are water insoluble but adsorb water, and sodium tauro- 24,25-dihydrofusidate (STDHF), which is surface active, are two promising enhancer systems promoting the nasal absorption of drugs by different mechanisms. These systems are discussed in this review. I. Introduction Systemically acting peptides and proteins are normally administered by parenteral injection. These have consisted of traditional sterile preparations, e.g., small volume parenterals (SVP) or lyophilized products. Because of the problems related to injections such as phobia for needles/syringes, pain, etc., the search for a non-parenteral alternative has been intensive. One of the most promising options is the nasal route. Nasal administration of drugs is not new and has been used since ancient times to give drugs locally or systemically. The subject has recently been reviewed by Chien et al. 1. The nasal cavity has a rather porous endothelial membrane and the mucosa is richly vascularized. The total area is rather large owing to the anatomy of the cavity and the microvilli structure of the epithelial cells. The most important advantage with the nasal route is how the blood circulation in the nose is linked to the systemic circulation, thus avoiding first- pass hepatic metabolism. The absorption rate profiles of many non-protein drugs given nasally are almost similar to that for i.v. administration. Some of the drawbacks with the nasal route are low bio-availability for large proteins, and that the drug itself or some component in the formulation is toxic/irritative to the mucosa. The nasal mucosa is enzymatically active, which has to be considered when dealing with peptides and proteins. Further, the physiological status of the nasal cavity also influences drug absorption through the nose. This review will highlight the problems with nasal administration of peptides and attempts to overcome those problems. The anatomy and physiology of the nasal cavity will also be briefly described. II. Nasal physiology The primary function of the nose in humans is to modify the inspired air 2 in such a way that it is heated, humidified and filtered of particles of different kinds, i.e., dust and bacteria. Another major function is the olfaction. The anatomy and physiology of the nose are well adapted to meet these needs.
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`NASAL DELIVERY OF PEPTIDE DRUGS 167 Unlike the lower airways that have a very low resistance to the airflow, the anatomy of the nasal cavity results in a high air resistance (Fig. 1). This structure ensures close contact between the air stream and the mucosal surface. The nasal epithelium consists mostly of ciliated columnar cells, goblet cells, non-ciliated columnar cells and basal cells. The epithelium is ciliated behind the nostril. These ciliated cells transport mucus and trapped particles backwards to the pharynx with a flow-rate of approximately 5-6 mm/min. The nasal cavity has a depth of 12-15 cm and thus the total contact time for any particle administered is 20-30 min. Mucociliary clearance is one of the major physical barriers for the nasal absorption of drugs. The cilia transport a layer of mucus produced by the goblet cells, nasal glands and lacrimal glands 3. The rpucus consists of water electrolytes, ~95-97% , 1-2% and 2-3% proteins, respectively. The protein content consists of glycoproteins, proteolytic enzymes, secretory proteins and plasma proteins. The proteolytic activity in the nasal mucus is a further hindrance to nasal absorption of drugs 4,5. The pH in the mucus layer of the nasal cavity is about 5.5-6.5 6, which is optimal for the proteolytic enzymes and the maintenance of the enzymatic barrier. Any deviation from the optimal pH, giving inactivation of the enzymes, can increase the probability of microbial infection. The nasal glands are mostly cholinergically innervated, whereas the vascular system is adrenergically innervated 7. Drugs that have an effect on these systems, locally or systemically, will also affect the status of the mucosal membrane. Changes in the nasal cavity by disease may also influence nasal ) Fig. 1. Anatomy and physiology of the nose. Left: diagram of entire upper airway seen from the midline. The dashed line just beyond the nostril marks the beginning of the nasal valve, whereas the dotted line shows approximately the beginning of the ciliated epithelium region. The dashed line near the nasopharynx indicates the posterior termination of the nasal septum. Right: the stippled areas above indicate the olfactory airway. The clear areas represent the main nasal airway which is the site primarily reached by the medication with drops or aerosols. The hatched areas mark the meatal spaces. (From Ref. 2, reproduced with permission of Elsevier).
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`168 P. EDMAN AND E. BJORK penetration. For instance, nasal obstruction caused by nasal polyposis reduces the absorption 8. Chronic and allergic rhinitis decrease mucociliary clearance time due to extensive mucus production 9. These and other pathological conditions will potentially modify the bioavailability of drug administered by the nasal route. III. Some basic characteristics of existing nasal drug delivery systems A few peptide formulations for nasal administration are available on the Swedish market I0. These products disperse sprays or drops into the nasal cavity by means of rhinyle catheters, pipettes or metered dose spray pumps. The factors that govern the systemic bioavailability of a peptide given by the nasal route can be divided roughly into three categories: -- physicochemical characteristics of the peptide, such as molecular size, structure and hydrophilicity; -- biochemical and physiological factors, such as enzymatic degradation in the mucosa and nasal mucociliary clearance; --pharmaceutical formulation, such as clearance and deposition of the delivery system in the nasal cavity, preservatives in the preparation and package. The effect of drug hydrophilicity on the absorption rate has been clearly shown by Corbo et al. 11 using progesterone as a model drug. The monohydroxy, dihydroxy and trihydroxy derivatives were prepared and it was clear that the systemic bioavailability decreased with increasing hydrophilicity of the drug. A linear relation was obtained when the rate constant of absorption was plotted against the log partition coefficient (octanol/water). According to McMartin et al. 12, there are two mechanisms of transport: a fast transport that is dependent on hydrophilicity and a slower rate dependent on molecular weight. The 'slower' transport rate is, nevertheless, fast enough to allow high absorption of low-molecular-weight hydrophilic drugs. The effect of molecular weight on absorption rate is related to the effective size of the molecule. Cyclic peptides are absorbed much better than linear ones 12. Peptidase inhibitors may be used to circumvent presystemic metabolism of intranasal administered peptides. The nasal mucosa is by itself an enzymatic barrier consisting of several different proteolytic/hydrolytic enzymes. The aminopeptidase activities in nasal and ileal mucosal homogenates from the albino rabbit when measured at a protein concentration of approx. 10 mg/ml are similar 13. The activities were given as the half-life of degradation of methionine enkephalin and were 16.3 +_ 1.4 and 15.1 _+ 2 min for nasal and ileal mucosa, respectively. Hussain et al. 14 have recently evaluated a new aminopeptidase inhibitor, boroleucine, and its effect on the degradation rate of leucine enkephalin in the nasal cavity of rat using an in vitro perfusing method. Boroleucine at a concentration of 0.1 gM prevented degradation of the enkephalin and the effect
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`NASAL DELIVERY OF PEPTIDE DRUGS 169 TABLE I DIFFERENT ABSORPTION-PROMOTING SUBSTANCES/ADJUVANTS USED IN NASAL DRUG DELIVERY OF PAPTIDES/PROTEINS Adjuvant Refs. Surfactants, non-ionic such as polyoxyethylene 9-1aurylether 5,19-23 Surfactants, anionic such as sodium lauryl-sulfate and saponins 5,19,20 Bile salts and derivatives 5,19,20,22-28 Fatty acids/phospholipids 29,30 Starch microspheres/powder 31 34 Sodium tauro-24,25-dihydrofusidate 35-37 Bacitracin 38 Glycyrrhetinic acid derivatives 39 Gels 40 Bile salt-fatty acid mixed micelles 41,42 was reversed when the inhibitor was omitted. The inhibitory concentrations of bestatin and puromycin were 0.1 mM and 1 mM, respectively, but even at these levels equivalent effects to boroleucine were not achieved. Peptidase inhibitors like boroleucine are potential pharmaceutical adjuvants. Inhaled/instilled particles are cleared from the nasal cavity by nasal mucociliary clearance. Thus every pharmaceutical system intended for intranasal use will interact with the nasal ciliary clearance mechanism. Preservatives such as methyl-p-hydroxybenzoate and propyl-p-hydroxybenzo- ate showed in a frog palate model to give reversible effect of the ciliary beat frequency while the effect of chlorobutanol was irreversible. In this model thiomersal gave no inhibiting effect of the ciliary beating 15. Furthermore, the rheological properties of the mucus layer can change after contact with pharmaceutical formulations. This will certainly affect the clearance and exposure of drugs to the mucosa. Instillation of drugs into the nasal cavity of humans also presents technical difficulties. In general, spray solutions are better than drops 16. Several novel devices have been developed to secure a reproducible dosing of drug into the nose and to improve handling. Intranasal administration of drugs, especially peptides, is attractive, and for some peptides also effective. But, in general, the route is associated with low bioavailability, local toxicity/irritation and is adversely affected by local disorders such as rhinitis and pathophysiological changes. Nevertheless, it has been shown that the common cold and rhinitis do not decrease the bioavailability of buserelin and desmopressin 17,18. Even though the nasal route is attractive with acceptable compliance, the overwhelming problem is bioavailability. IV. Enhancer systems To improve nasal peptide bioavailability, absorption-promoting systems/ enhancers have to be used. Much biopharmaceutical research in this area during the past decade has been devoted to finding and testing different
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`170 P. EDMAN AND E. BJORK absorption-promoting systems. Table I lists enhancer systems from the literature. The most commonly used absorption enhancers are: surfactants both non-ionic (such as laureth-9) and anionic (such as saponins, sodium laurylsulfate), bile acids (such as taurocholate, cholate and glycocholate) and bacitracin 5,21,36. All systems improve bioavailability, but the effects are often associated with adverse reactions in the mucosa. A clear correlation was shown by Hirai et al. 5 between insulin uptake and membrane lysis for the non-ionic surfactants. The bile acid derivatives break down mucous membrane structure 43, induce protein losses, irritation and morphological changes in the nasal mucosa 44. Sodium taurodihydrofusidate (STDHF) is an enhancer system which is claimed to be more biocompatible than bile acids. A comparison between STDHF and bile acids showed that STDHF is 5 times less hemolytic on a molar basis than the bile salts 35. Further, studies with insulin and STDHF in rats and rabbits showed good enhancement of nasal insulin absorption. Novel enhancers such as phospholipids, especially lysophosphatidylcholine 30, and starch microspheres 31,32 have also been shown to act efficiently as absorption enhancers. Crosslinked starch in the form of a bead 45 ~tm in diameter has probably the same mechanism of action as the water-insoluble powder system introduced by Nagai et al. 34. Both systems are administered as a dry powder. After instillation in the nasal cavity they adsorb water and swell. This process affects the superficial epithelial cell layer, probably by temporary dehydration, inducing a slight widening of the tight junctions. itt~ sc 1 L L L I I 1 0 0 L,O GO 80 100 120 'i40 160 180 Tir'ne (rnin) Fig. 2. Clearance of different microsphere systems and of two control systems from the nasal cavity; e, DEAE-dextran microspheres; A, starch microspheres; C), albumin microspheres; A, lomudal nasal solution; , lomudal nasal powder. (From Ref. 45, reproduced with permission of Elsevier).
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`NASAL DELIVERY OF PEPTIDE DRUGS 171 V. New enhancer systems In the previous section, the problems/drawbacks with existing enhancer systems, e.g., bile acids, were reviewed. Since nasal biopharmaceutical research is currently directed on absorption and bioavailability, we shall describe in more detail the most recently introduced enhancer systems, namely micro- spheres, STDHF and glycyrrhetinic acid derivatives. The concept of using starch microspheres as a nasal drug-delivery system was introduced by Illum et al. 45. They presented a scintigraphic study on healthy volunteers with technetium-labelled spheres of different materials, e.g., DEAE-dextran, starch and albumin. The results shown in Fig. 2 indicate that starch microspheres and DEAE-dextran spheres have a significant slower clearance than nasal solution and powder (Lomudal). Approx. 50% of the administered dose of starch microspheres remained in the nasal cavity after 180 rain. A preliminary autoradiographic study with 14C-labelled spheres in rats indicates that the microspheres are cleared from the nasal cavity more or less intact. The influence of this delayed transport of spheres from the nose on the biological effects of co-administered drug has been studied by Bj6rk and Edman 31 and Illum et al. 32. Their findings established that starch microspheres act as an absorption promotor. Insulin and starch microspheres given as a powder nasally to rats rapidly decreased the blood glucose level. The maximal decrease in blood glucose was achieved within 30-40 min at a dose of 1.7 U per kg body weight (Fig. 3). The maximal concentration of immunoreactive insulin in plasma was obtained after 8 min. Calculated bioavailability of insulin was approximately 30%. Soluble insulin (2 U/kg body weight), on the other hand, gave a negligible effect on the blood glucose level. Recently 46, the same microsphere system was used with insulin in sheep. The relative bioavailability of insulin with microspheres was found to be 10.7% whereas soluble insulin had a bioavailability of up to 1%. Combination of the microsphere system with lysophosphatidylcholine (LPC), a biological surfac- tant, increased the bioavailability to 31.5%. Administration of biosynthetic human growth hormone (hGH) in sheep using microspheres and the combination of spheres and LPC gave an improved relative bioavailability of 2.7% and 14.4%, respectively 47. A nasal solution of hGH had a bioavailability of 0.1%. Addition of LPC gives a significant promotion of the absorption of peptides through the nasal mucosa. It is well known that LPC is membrane active and thereby should facilitate the transport of drugs across the nasal membrane. The effectiveness of LPC/starch microspheres is further shown with the hydrophilic compound, gentamicin, in sheep. Using LPC and starch microspheres the bioavailability of gentamicin reached 57.3%. The microspheres alone gave a bioavailability of 9.7%, whereas LPC alone had no effect. Thus, the combination acts efficiently and the enhancing effect is synergistic 32. The action of starch microspheres is due presumably to their ability to take up water and swell or gel. If the ratio between the amount of spheres administered and the amount of water available
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`172 P. EDMAN AND E. BJORK in the nasal cavity is such that the spheres are not maximally swelled, then the underlying cells will be temporarily dehydrated and will shrink, giving a temporarily widening of the tight junctions. Hence, the probability for paracellular transport is significantly improved. A dose-response relationship exists between the amount of spheres and their impact on bioavailability of insulin 33. Additional to changes in membrane permeability seen with the spheres, there are also the changes in mucociliary clearance which contribute to the mechanism of absorption enhancement with starch microspheres 45. Histological studies in rabbits after long-term administration of starch microspheres nasally revealed only a mild hyperplasia on the nasal septum wall with an increased number of goblet cells. An overall evaluation of the Z o g e~ e- 50 100 () 3'0 6'0 120 180 240 Time (min) Fig. 3. Change in blood glucose in rats after intranasal administration of insulin. © ©, Soluble insulin 2.0 IU/kg. O--O, Degradable starch microspheres + insulin 1.70 IU/kg. x--x, Empty Degradable starch microspheres 0.5 mg/kg. Mean _ S.D., n = 68. (From Ref. 31, reproduced with permission of Elsevier).
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`NASAL DELIVERY OF PEPTIDE DRUGS 173 findings indicates that starch microspheres are biocompatible 48. Further, no hemolytic activity was seen with the starch microspheres. Glycyrrhetinic acid derivatives have recently been suggested as a nasal promotor of insulin absorption 39. Glycyrrhetinic acid and glycyrrhizine acid are components from Glycyrrhiza glabra, showing a surfactant action similar to bile acids and saponins. In a study by Mishima et al. 39, they showed that these substances and derivatives thereof promoted absorption of insulin across the nasal mucosa in rats. The hemolytic activity of these derivatives was found to be less than that of sodium laurate but stronger than that of sodium glycocholate. Leucine aminopeptidase activity was inhibited at rather low concentrations. However, whether these compounds can be used as a promotor system for long-term use is still uncertain. STDHF is one of the most promising candidates for enhancing intranasal uptake of drugs. It was originally synthesized as a potential antibiotic by Leo Pharmaceuticals in Denmark. Carey and coworkers 49 were first to report the enhancing activity of STDHF on transmucosal insulin absorption. STDHF is a detergent-like adjuvant with a critical micellar concentration (CMC) around 2.5 mM or 0.16% (w/v). In most of the studies, STDHF concentrations of 0.5% (w/v) or 1.0% (w/v) were used. Longenecker and coworkers 35 showed the effect of STDHF on insulin uptake in sheep (Fig. 4). Three doses of insulin (0.25, 0.5 and 1.0 U/kg) were used together with 1% (w/ v) STDHF and a linear relationship was obtained between the insulin dose and the AUC values. Other substances investigated in combination with STDHF 500 4OO ,~300 2OO Ioo o' o J~i --o-- 1.0 u/kg ~'\ --~-- 0.5 ulkg I ...... 0.25 u/kg ~ ~ ~ I l I I "1 ""1"' i'"f~''t fo 20 30 4.0 50 60 Time (min.) Fig. 4. Influence of insulin dose on intranasal insulin absorption in sheep. Kinetics of insulin absorption at doses of 0.25, 0.50 and 1.0 U/kg. (From Ref. 35, reproduced with permission of American Pharmaceutical Association).
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`174 P. EDMAN AND E. BJI3RK are Phenol red 49, buserelin and LHRH 38 and human growth hormone (hHG) 37. Human growth hormone given nasally together with 0.5% (w/v) STDHF to rats showed a dose-dependent uptake up to 1.5 mg/kg 37. The optimal enhancing effect of STDHF is close to the CMC concentration. An additional increase of concentration above the CMC concentration gives no further effect. The mode of action of STDHF is not fully understood. There are, however, several hypotheses: (a) a complex formation with the peptide above the CMC concentration; (b) a surface-active effect on the mucosa with membrane- permeability change; and (c) an enzyme inhibition. STDHF has so far been shown to be less toxic than the bile acids and non-ionic surface active agents. The hemolytic activity of STDHF was considerably lower than sodium deoxycholate and laureth-9 of the same w/v % concentration 35. Hermens and coworkers 50 have tested the action of several enhancers, including STDHF, on ciliary movement. They found that all enhancers have a ciliostatic/ toxic effect. Changes in the morphology of the nasal mucosa after STDHF exposure were classified by Ennis and coworkers 51 into four classes: (1) mucosal surface integrity; (2) ciliary morphology; (3) mucus/extracellular debris; and (4) presence of red blood cells. STDHF 0.5% (w/v) showed only small changes in the first two classes after 15 min continuous exposure. 1% (w/v) STDHF resulted in larger changes in classes 1-3. Sodium taurodeoxycholate and sodium deoxycholate showed the largest changes in all classes. This study, like many others on the biocompatability of enhancers, lacks studies on chronic administration. Only after at least 90 days can the long-term effect of the enhancer be evaluated. However, all data available today and summarized indicate that STDHF is one of the most promising enhancer systems. VI. Conclusion Nasal administration of drugs, particularly peptides, is attractive but suffers from low bioavailability, local irritation and toxicity on long-term use. To achieve reproducibility with dosing and further acceptable economy in the treatment, a bioavailability of 1-2% for an expensive recombinant peptide is not acceptable. Therefore, it is necessary to find a biocompatible absorption promotor. The proposed promotors act by different mechanisms either separately or jointly. They may alter the mucus layer, inhibit proteases in the nasal mucosa, increase the membrane fluidity, widen the tight junctions, etc. However, a major drawback with all these enhancers is their local irritation and toxicity on the nasal mucosa. Further, the immunological consequences of nasal administration of peptides have also to be investigated, especially the local immunization and production of IgA, which can induce inflammatory reactions and prevent absorption of biologically active peptides. The optimal absorption system should be well tolerated, cheap, and act pulse-wise, widening
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`NASAL DELIVERY OF PEPTIDE DRUGS 175 the tight junctions for a short period (a few minutes). Starch microspheres, water-insoluble and swellable powders, and phospholipids are novel absorption systems which have promising properties but need further characterization. References 1 Chien, Y.W., Su, K.S.E. and Chang, S.F. (1989) Nasal systemic drug delivery, Marcel Dekker, New York, Vol. 39. 2 Proctor, D.F. (1982) The Upper Airway. In: D.F. Proctor and I. Andersen (Eds.), The nose, upper airway physiology and the atmospheric environment, Elsevier, Amsterdam, pp. 23-43. 3 Marom, Z., Shelhamer, J. and Kaliner, M. (1984) Nasal mucus secretion, Ear Nose Throat J. 63, 36-44. 4 Stratford, R.E. and Lee, V.H.L. (1986) Amino peptidase activity in homogenates of various absorptive mucosae in the albino rabbit: implications in peptide delivery, Int. J. Pharm. 30, 73 82. 5 Hirai, S., Yashiki, T. and Mima, H. (1981) Mechanisms for the enhancement of the nasal absorption of insulin by surfactants, Int. J. Pharm. 9, 173 184. 6 Fabricant, N.D. (1941) Significance of the pH of nasal secretions in situ, Arch. Otolaryngol. 34, 150. 7 Millonig, A.F., Harris, H.E. and Gardner, W.J. (1950) Effect of anatomic denervation on nasal mucosa, Arch. Otolaryngol. 52, 359 368. 8 Proctor, D.F. (1985) Nasal physiology in intranasal drug administrations. In: Y.W. Chien (Ed.), Transnasal Systemic Medications, Elsevier, Amsterdam, pp. 101-106. 9 Maurizi, M., Paludetti, G., Toolisco, T., Almadori, G., Ohaviani, F. and Zappone, C. (1984) Ciliary ultrastructure and nasal mucociliary clearance in chronic and allergic rhinitis, Rhinology 22, 233-240. 10 Harris, A. (1986) Biopharmaceutical aspects on the intranasal administration of peptides. In: S.S. Davis, L. Illum and E. Tomlinson (Eds.), Delivery Systems for Peptide Drugs, NATO ASI Series, Plenum Press, New York, pp. 191~04. 11 Corbo, D.C., Liu, J.C. and Chien, Y.W. (1989) Drug absorption through mucosal membranes: effect of mucosal route and penetrant hydrophilicity, Pharm. Res. 6, 848-852. 12 McMartin, C., Hutchinson, L.E.F., Hyde, R. and Peters, G.E. (1987) Analysis of structural requirements for the absorption of drugs and macromolecules from the nasal cavity, J. Pharm. Sci. 76, 535-540. 13 Dodda Kashi, S. and Lee, V.H.L. (1986) Enkephalin hydrolysis in homogenates of various absorptive mucosae of the albino rabbit: similarities in rates and involvement of aminopepti- dases, Life Sci. 38, 2019-2028. 14 Hussain, M.A., Koval, C.A., Shenvi, A.B. and Aungst, B.J. (1990) Recovery of rat nasal mucosa from the effects of aminopeptidase inhibitors, J. Pharm. Sci. 79, 398-400. 15 Batts, A.H., Marriott, C., Martin, G. and Bond, S.W. (1989) The effect of some preservatives used in nasal preparations on mucociliary clearance, J. Pharm. Pharmacol. 41, 156-159. 16 Harris, A.S., Nilsson, I.M., Wagner, Z.G. and Alkner, U. (1986) Intranasal administration of peptides: nasal deposition, biological response and absorption of desmopressin, J. Pharm. Sci. 75, 1085-1088. 17 Larsen, C., Niebuhr Jorgensen, M., Tommerup, B., Mygind, N., Dagrosa, E.E., Grigoleit, H.G. and Malerczyk, V. (1987) Influence of experimental rhinitis on the gonadotropin response to intranasal administration of buserelin, Eur. J. Clin. Pharmacol. 33, 155-159. 18 Olanoff, L.S., Titus, C.R., Shea, M.S., Gibson, R.E. and Brooks, C.D. (1987) Effect of intranasal histamine on nasal mucosal blood flow and the antidiuretic activity of desmopressin, J. Clin. Invest. 80, 89(~895. 19 Hirai, S., Ikenaga, T. and Matsuzawa, T. (1977) Nasal absorption of insulin in dogs, Diabetes 27, 296-299.
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`176 P. EDMAN AND E. BJORK 20 Hirai, S., Yashiki, T. and Mima, H. (1981) Effect of surfactants on the nasal absorption of insulin in rats, Int. J. Pharm. 9, 165-172. 21 Daugherty, A.L., Liggitt, H.D., McGabe, J.G., Moore, J.A. and Patton, J.S. (1988) Absorption of recombinant methionyl-human growth hormone (Met-hGH) from rat nasal mucosa, Int. J. Pharm. 45, 197-206. 22 Hayakawa, E., Yamamoto, A., Shoji, Y. and Lee, V.H.L. (1989) Effect of sodium glycocholate and polyoxyethylene-9-1aurylether on the hydrolysis of varying concentrations of insulin in the nasal homogenates of the albino rabbit, Life Sci. 45, 167-174. 23 Pontiroli, A.E., Alberetto, M., Calderara, A., Pajetta, E. and Pozza, G. (1989) Nasal absorption of glucagon and human calcitonin to healthy subjects: a comparison of powders and spray solutions and of different enhancing agents, Eur. J. Pharmacol. 37, 427-430. 24 Hirata, Y., Yokosuka, T., Kashara, T., Kikuchi, M. and Ooi, K. (1978) Nasal administration of insulin in patients with diabetes. In: S. Baba and S. Kaneko (Eds.), Proceedings of a Symposium of Proinsulin, Insulin and c-Peptide, Elsevier/Excerpta Medica, Amsterdam, pp. 319-326. 25 Pontiroli, A.E., Alberetto, M., Secchi, A., Dossi, G., Bosi, I. and Pozza, G. (1982) Insulin given intranasally induces hypoglycaemia in normal and diabetic subjects, Br. Med. J. 284, 303 306. 26 Moses, A.C., Gordon, G.S., Carey, M.C. and Flier, J.S. (1983) Insulin administered intranasally as an insulin-bile salt aerosol, Diabetes 32, 104(~1047. 27 Pontiroli, A.E., Alberetto, M., Pajetta, E., Calderara, A. and Gozza, E. (1987) Human insulin plus sodium glycocholate in a nasal spray formulation: improved bioavailability and effectiveness in normal subjects, Diabetes Metab. 13, 441-443. 28 Aungst, B.J., Rogers, N.J. and Shefter, E. (1988) Comparison of nasal, rectal, buccal, sublingual and intramuscular insulin efficacy and the effects of a bile salt absorption promotor, J. Pharmacol. Exp. Ther. 244, 23 27. 29 Mishima, M., Wakita, Y. and Nakano, M. (1987) Studies on the promoting effects of medium chain fatty acid salt on the nasal absorption of insulin in rats, J. Pharmacobiodyn. 10, 624~631. 30 Illum, L., Farraj, N.F., Critchley, H., Johansen, B.R. and Davis, S.S. (1989) Enhanced nasal absorption of insulin in rats using lysophosphatidylcholine, Int. J. Pharm. 57, 49-54. 31 Bj6rk, E. and Edman, P. (1988) Degradable starch microspheres as a nasal delivery system for insulin, Int. J. Pharm. 47, 233-238. 32 Illum, L., Farraj, N., Critchley, H. and Davis, S.S. (1988) Nasal administration of gentamicin using a novel microsphere delivery system, Int. J. Pharm. 46, 261 265. 33 Bj6rk, E. and Edman, P. (1990) Characterization of degradable starch microspheres as a nasal delivery system for drugs, Int. J. Pharm. 62, 187 192. 34 Nagai, T., Nishimoto, Y., Nambu, N., Suzuki, Y. and Sekine, K. (1984) Powder dosage form of insulin for nasal administration, J. Contr. Release 1, 15--22. 35 Longenecker, J.P., Moses, A.C., Flier, J.S., Silver, R.D., Carey, M.C. and Dubovi, E.J. (1987) Effects of sodium taurodihydrofusidate on nasal absorption of insulin in sheep, J. Pharm. Sci. 76, 351 355. 36 Deurloo, M.J.M., Hermens, W.A.J.J., Romeyn, S.G., Verhoef, J.C. and Merkus, F.W.H.M. (1989) Absorption enhancement of intranasally administered insulin by sodium taurodihydro- fusidate (STDHF) in rabbits, Pharm. Res. 6, 853-856. 37 Baldwin, P.A., Klingbeil, C.K., Grimm, C.J. and Longenecker, J.P. (1990) The effect of sodium tauro-24,25-dihydrofusidate on the nasal absorption of human growth hormone in three animal models, Pharm. Res. 7, 547- 552. 38 Raehs, S.C., Sandow, J., Wirth, K. and Merkle, H.P. (1988) The adjuvant effect of bacitracin on nasal absorption of gonadorelin and buserelin in rats, Pharm. Res. 5, 689-693. 39 Mishima, M., Okada, S., Wakita, Y. and Nakano, M. (1989) Promotion of nasal absorption of insulin by glycyrrhetinic acid derivatives. I, J. Pharmacobiodyn. 12, 31-36. 40 Morimoto, K., Morisaka, K. and Kamada, A. (1985) Enhancement of nasal absorption of insulin and calcitonin using polyacrylic acid gel, J. Pharm. Pharmacol. 37, 134~136. 41 Tengamnuay, P. and Mitra, A.K. (1990) Bile salt-fatty acid mixed micelles as a nasal absorption promoter of peptides. 1. Effects of ionic strength, adjuvant composition, and lipid structure on the nasal absorption of D-ArgZKyotorphin, Pharm. Res. 7, 127 133.
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