Nasal absorption of dihydroergotamine from liquid and powder formulations in rabbits

Spray dried powders for nasal delivery: Process and formulation considerations

Powders for nasal delivery have been recognized as advantageous dosage forms over liquids due to increased stability and residence time on nasal mucosa, with improved bioavailability. They can be manufactured by spray-drying, allowing the optimization of the particle properties that are critical to guarantee nasal deposition, as size and shape. It is also a scalable and flexible method already explored extensively in the pharmaceutical industry. However, it is important to understand how process parameters, particle physical properties and formulation considerations affect the product performance. Hence, this review aims to provide an overview of nasal powder formulation and processing through spray drying, with an emphasis on the variables that impact on performance. To this purpose, we describe the physical, biological and pharmacological phenomena prior to drug absorption as well as the most relevant powder properties. Formulation considerations including qualitative and quantitative composition are then reviewed, as well as manufacturing considerations including spray drying relevant parameters.

Pain management with transdermal drug administration: A review

Pain management is an urgent issue to solve with complex mechanisms. Localized acute pain requires rapid and accurate delivery of drugs with less distribution in the blood circulation while chronic pain requires controlled release of drugs with long drug retention time. The transdermal route, a promising way with high patient compliance was known for painless delivery, long drug retention time, stable blood concentration, easily controlled dosage and release rate as well as the fewer side effects. This review presents transdermal route for pain management according to the different sites of action which drugs aim to reach, and illustrates different analgesic mechanisms, dosage forms, transdermal enhancements and clinical applications. In addition, the review concludes the difference of pain types and presents the future aims of pain management, thereby providing a reference for researches focusing on percutaneous analgesia.

Evaluation of Ribavirin-Poloxamer Microparticles for Improved Intranasal Absorption

Ribavirin is a water-soluble antiviral compound which, owing to its inability to cross the blood–brain barrier, has limited effectiveness in treating viruses affecting the central nervous system. Direct nose-to-brain delivery was investigated for ribavirin in combination with poloxamer 188, an excipient known to enhance the absorption of drug compounds administered intranasally. Composite solid microparticles suitable for intranasal insufflation were prepared by suspending fine crystals of ribavirin in a matrix of poloxamer 188, which were cryogenically milled and characterized to ensure that ribavirin remained stable throughout preparation. In vitro diffusion of ribavirin across a semi-permeable regenerated cellulose membrane showed comparable cumulative drug release after 180 min from both fine solid particles (<20 µm) and 1:1 ribavirin:poloxamer microparticles (d₅₀ = 20 µm); however, the initial release from polymer microparticles was slower, owing to gel formation on the membrane surface. When solid ribavirin was directly deposited on excised olfactory mucosa, either as fine drug particles or 1:1 ribavirin:poloxamer microparticles, permeation was significantly increased from microparticles containing poloxamer 188, suggesting additional interactions between the polymer and olfactory mucosa. These data indicate that for highly water-soluble drugs such as ribavirin or drugs subject to efflux by the nasal mucosa, a formulation of poloxmer-containing microparticles can enhance permeability across the olfactory epithelium and may improve direct nose-to-brain transport.

Physico-Chemical and In Vitro Characterization of Chitosan-Based Microspheres Intended for Nasal Administration

The absorption of non-steroidal anti-inflammatory drugs (NSAIDs) through the nasal epithelium offers an innovative opportunity in the field of pain therapy. Thanks to the bonding of chitosan to the nasal mucosa and its permeability-enhancing effect, it is an excellent choice to formulate microspheres for the increase of drug bioavailability. The aim of our work includes the preparation of spray-dried cross-linked and non-cross-linked chitosan-based drug delivery systems for intranasal application, the optimization of spray-drying process parameters (inlet air temperature, pump rate), and the composition of samples. Cross-linked products were prepared by using different amounts of sodium tripolyphosphate. On top of these, the micrometric properties, the structural characteristics, the in vitro drug release, and the in vitro permeability of the products were studied. Spray-drying resulted in micronized chitosan particles (2–4 μm) regardless of the process parameters. The meloxicam (MEL)-containing microspheres showed nearly spherical habit, while MEL was present in a molecularly dispersed state. The highest dissolved (>90%) and permeated (~45 µg/cm²) MEL amount was detected from the non-cross-linked sample. Our results indicate that spray-dried MEL-containing chitosan microparticles may be recommended for the development of a novel drug delivery system to decrease acute pain or enhance analgesia by intranasal application.

Opportunity and challenges of nasal powders: Drug formulation and delivery

In the field of nasal drug delivery, among the preparations defined by the European Pharmacopoeia, nasal powders facilitate the formulation of poorly water-soluble active compounds. They often display a simple composition in excipients (if any), allow for the administration of larger drug doses and enhance drug diffusion and absorption across the mucosa, improving bioavailability compared to nasal liquids. Despite the positive features, however, nasal products in this form still struggle to enter the market: the few available on the market are Onzetra Xsail® (sumatriptan) for migraine relief and, for the treatment of rhinitis, Rhinocort® Turbuhaler® (budesonide), Teijin Rhinocort® (beclomethasone dipropionate) and Erizas® (dexamethasone cipecilate). Hence, this review tries to understand why nasal powder formulations are still less common than liquid ones by analyzing whether this depends on the lack of (i) real evidence of superior therapeutic benefit of powders, (ii) therapeutic and/or commercial interest, (iii) efficient manufacturing methods or (iv) availability of suitable and affordable delivery devices. To this purpose, the reader's attention will be guided through nasal powder formulation strategies and manufacturing techniques, eventually giving up-to-date evidences of therapeutic efficacy in vivo. Advancements in the technology of insufflation devices will also be provided as nasal drug products are typical drug-device combinations.

Intranasal Eutectic Powder of Zolmitriptan with Enhanced Bioavailability in the Rat Brain

Intranasal administration can potentially deliver drugs to the brain because of the proximity of the delivery site to the olfactory lobe. We prepared triturates of micronized or crystalline zolmitriptan with a GRAS substance, nicotinamide, to form a eutectic. We characterized the formulation using differential scanning calorimetry, powder X-ray diffraction, and FTIR spectroscopy to confirm its eutectic nature and generated a phase diagram. The eutectic formulation was aerosolized using an in-house insufflator into the nares of rats. Groups of rats received zolmitriptan intravenously or intranasally, or intranasal eutectic formulation. Zolmitriptan was estimated in the olfactory lobe, cerebral cortex, cerebellum, and blood plasma at different time-points by LC-MS. Pharmacokinetics in these tissues indicated the superiority of the intranasal eutectic formulation for brain targeting when compared with results of IV solution and intranasal pure zolmitriptan powder. Enhancement of nose-to-brain transport is likely to have resulted from more rapid dissolution of the eutectic as compared to pure drug.

Nasal-nanotechnology: revolution for efficient therapeutics delivery

CONTEXT

In recent years, nanotechnology-based delivery systems have gained interest to overcome the problems of restricted absorption of therapeutic agents from the nasal cavity, depending upon the physicochemical properties of the drug and physiological properties of the human nose.

OBJECTIVE

The well-tolerated and non-invasive nasal drug delivery when combined with the nanotechnology-based novel formulations and carriers, opens the way for the effective systemic and brain targeting delivery of various therapeutic agents. To accomplish competent drug delivery, it is imperative to recognize the interactions among the nanomaterials and the nasal biological environment, targeting cell-surface receptors, drug release, multiple drug administration, stability of therapeutic agents and molecular mechanisms of cell signaling involved in patho-biology of the disease under consideration.

METHODS

Quite a few systems have been successfully formulated using nanomaterials for intranasal (IN) delivery. Carbon nanotubes (CNTs), chitosan, polylactic-co-glycolic acid (PLGA) and PLGA-based nanosystems have also been studied in vitro and in vivo for the delivery of several therapeutic agents which shown promising concentrations in the brain after nasal administration.

RESULTS AND CONCLUSION

The use of nanomaterials including peptide-based nanotubes and nanogels (NGs) for vaccine delivery via nasal route is a new approach to control the disease progression. In this review, the recent developments in nanotechnology utilized for nasal drug delivery have been discussed.

Influence of polymeric microcarriers on the in vivo intranasal uptake of an anti-migraine drug for brain targeting

The objective of this study was to investigate the effect of polymeric microcarriers on the in vivo intranasal uptake of an anti-migraine drug for brain targeting. Mucoadhesive powder formulations consisted of antimigraine drug, zolmitriptan, and chitosans (various molecular weights and types) or hydroxypropyl methylcellulose (HPMC). Their suitability for nasal administration was evaluated by in vitro and ex vivo mucoadhesion and permeation tests. The formulations based on chitosan glutamate (CG) or HPMC were tested in vivo because they showed good mucoadhesive properties and altered the permeation rate of the drug. The in vivo results from intravenous infusion and nasal aqueous suspension of the drug or nasal particulate powders were compared. The plasmatic AUC values obtained within 8h following intravenous administration appeared about three times higher than those obtained by nasal administration, independent of the formulations. Zolmitriptan concentrations in the cerebrospinal fluid obtained from nasal and intravenous administrations were, respectively, 30 and 90 times lower than the concentrations of the drug in the blood. Thus, nasal administration potentiated the central zolmitriptan activity, allowing a reduction in the drug peripheral levels, with respect to the intravenous administration. Among nasally administered formulations, CG microparticles showed the highest efficacy in promoting the central uptake of zolmitriptan within 1h.

Cyclodextrins in delivery systems: Applications

Cyclodextrins (CDs) are a family of cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. CD molecules are relatively large with a number of hydrogen donors and acceptors and, thus in general, they do not permeate lipophilic membranes. In the pharmaceutical industry, CDs have mainly been used as complexing agents to increase aqueous solubility of poorly soluble drugs and to increase their bioavailability and stability. CDs are used in pharmaceutical applications for numerous purposes, including improving the bioavailability of drugs. Current CD-based therapeutics is described and possible future applications are discussed. CD-containing polymers are reviewed and their use in drug delivery is presented. Of specific interest is the use of CD-containing polymers to provide unique capabilities for the delivery of nucleic acids. Studies in both humans and animals have shown that CDs can be used to improve drug delivery from almost any type of drug formulation. Currently, there are approximately 30 different pharmaceutical products worldwide containing drug/CD complexes in the market.

Nasal administration of metoclopramide from different dosage forms: in vitro, ex vivo, and in vivo evaluation

Nasal drug delivery is an interesting route of administration for metoclopramide hydrochloride (MTC) in preventing different kind of emesis. Currently, the routes of administration of antiemetics are oral or intravenous, although patient compliance is often impaired by the difficulties associated with acute emesis or invasiveness of parenteral administration. In this perspective, nasal dosage forms (solution, gel, and lyophilized powder) of MTC were prepared by using a mucoadhesive polymer sodium carboxymethylcellulose (NaCMC). In vitro and ex vivo drug release studies were performed in a modified horizontal diffusion chamber with cellulose membrane and excised cattle nasal mucosa as diffusion barriers. The tolerance of nasal mucosa to the formulation and its components were investigated using light microscopy. In vivo studies were carried out for the optimized formulations in sheep and the pharmacokinetics parameters were compared with oral solution and IV dosage form. The release of MTC from solution and powder formulations was found to be higher than gel formulation (p < 0.05). Histopathological examination did not detect any severe damage. Hydroxypropyl-beta-cyclodextrin (HPbetaCD) used in powder formulations was found to be effective for enhancing the release and absorption of MTC. In contrast to in vitro and ex vivo experiments nasal bioavailability of gel is higher than those of solution and powder (p < 0.05). In conclusion, the NaCMC gel formulation of MTC with mucoadhesive properties with increased permeation rate is promising for prolonging nasal residence time and thereby nasal absorption.

Preparation of zolmitriptan-chitosan microparticles by spray drying for nasal delivery

The objective of this study was to use spray drying to prepare mucoadhesive dry powders of the antimigraine drug, zolmitriptan, in combination with the natural polymer, chitosan, for nasal administration. The effect of type, molecular weight, and proportion of chitosan on the powder and particle characteristics was also studied. Solutions containing different proportions of chitosans were prepared and spray dried. The chemical stability and content of the drug were determined by HPLC. The morphology and size range of the microparticles were also determined. Solid-state analysis was undertaken using thermal methods (DSC/MDSC and TGA), powder X-ray diffraction (PXRD), and Fourier transform infra-red spectroscopy (FT-IR). The drug release profiles were investigated and the time required to reach maximum solution concentrations (T(max)) was used for comparison. The drug was chemically stable, with a 93-105% loading in the microparticles. The microparticles were spherical with a narrow size distribution, irrespective of the formulation. Phase separation was observed for formulations containing less than 90% (w/w) chitosan, irrespective of the type. In contrast, in the formulation containing 90% (w/w) chitosan, the drug was molecularly dispersed. FT-IR studies showed that the bands corresponding to intermolecular hydrogen bonding were broader and more diffuse when zolmitriptan was amorphous. The formation of a hydrogen bond between drug and chitosans was also observed. T(max) increased as the proportion of chitosan decreased, and was proportional to the molecular weight of the chitosan in the formulation containing 90% (w/w) chitosan. Spray drying is a suitable technique for making mucoadhesive dry powders of zolmitriptan and chitosan for nasal application. The dispersion and release of the drug was affected by the properties and composition of the chitosan.

In vitro formulation optimization of intranasal galantamine leading to enhanced bioavailability and reduced emetic response in vivo

The purpose of the current investigation was to optimize an intranasal (IN) galantamine (an acetylcholinesterase inhibitor used for treatment of Alzheimer's disease) formulation using an in vitro tissue model, to correlate those results to in vivo bioavailability, and to compare emetic response to oral dosing. A design-of-experiments (DOE) based formulation screening employing an in vitro tissue model of human nasal epithelium was used to assess drug permeability, tight junction modulation, and cellular toxicity. In vivo studies in rats compared pharmacokinetic (PK) profiles of different formulations dosed intranasally. Finally, studies in ferrets evaluated PK and gastrointestinal (GI) related side effects of oral compared to nasal dosage forms. Galantamine permeation was enhanced without increasing cytotoxicity. Pharmacokinetic testing in rats confirmed the improved drug bioavailability and demonstrated an in vitro-in vivo correlation. Compared to oral dosing, IN galantamine resulted in a dramatically lowered incidence of GI-related side effects, e.g., retching and emesis. These findings illustrate that IN delivery represents an attractive alternative to oral dosing for this important Alzheimer's disease therapeutic. To our knowledge, the data herein represent the first direct confirmation of reducing GI-related side effects for IN galantamine compared to oral dosing.

Nasal clearance in health and disease

This paper reviews the anatomical and physiological factors of importance for nasal drug delivery and discusses in particular the influence of the nasal mucociliary clearance mechanism on the nasal absorption of drugs. The effect of nasal pathological conditions on the mucociliary clearance mechanism and the possible effect of such disease states on nasal drug transport are also discussed. Strategies for the exploitation of bioadhesive drug delivery systems and especially nasal absorption enhancers for the improvement of nasal drug delivery are evaluated to include considerations of the mechanism of action and correlation between the degree of bioadhesion and absorption enhancement and transport of drugs across the nasal membrane. A range of studies involving bioadhesive/absorption enhancer systems are detailed. A selected bioadhesive material, chitosan, which has been shown to have excellent absorption enhancer properties for a variety of drugs is discussed in some detail.

Cyclodextrins in drug delivery

Cyclodextrins are a family of cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. Cyclodextrin molecules are relatively large with a number of hydrogen donors and acceptors and, thus, in general they do not permeate lipophilic membranes. In the pharmaceutical industry cyclodextrins have mainly been used as complexing agents to increase aqueous solubility of poorly soluble drugs, and to increase their bioavailability and stability. Studies in both humans and animals have shown that cyclodextrins can be used to improve drug delivery from almost any type of drug formulation. However, the addition of cyclodextrins to existing formulations without further optimisation will seldom result in acceptable outcome. Currently there are approximately 30 different pharmaceutical products worldwide containing drug/cyclodextrin complexes on the market.

Preparation of prostaglandin E1-hydroxypropyl-β-cyclodextrin complex and its nasal delivery in rats

The potential use of hydroxypropyl-beta-cyclodextrin (HP-betaCD) in the solubilization and stabilization of prostaglandin E(1) (PGE(1)) was investigated. The solubility and chemical stability of PGE(1) were significantly improved upon complexation with HP-betaCD. The nasal delivery of PGE(1) from the complex formulation was also studied in Wistar rats and compared with intravenous administration. PGE(1) complex after nasal administration caused a rapid decrease of blood pressure and exhibited an obvious dose-efficacy relationship, showing results nearly similar to those obtained for intravenous route. The time to reach the peak effect (T(max)) was approximately 3-4 min. Except T(max), other pharmacodynamic parameter values such as the maximal percent of blood pressure decrease (E(max), %), the lasting time of effect (T(d)), and the area under the curve (AUC, blood pressure decrease % min) were increased with increasing the administered doses. The E(max), T(d), and in particular AUC values between doses were significantly different (P < 0.01), but T(max) between doses were not significantly different (P < 0.05). The AUC values per unit dose of PGE(1) for nasal administration, however, were smaller than those for intravenous route, probably due to the incomplete absorption of nasally administered PGE(1). Besides, the in vitro effect of the PGE(1) complex on nasal mucociliary movement was also investigated with a toad palate model. The PGE(1) complex formulation exerted only minor effect on nasal mucociliary movement. These results indicate that the PGE(1)-HP-betaCD complex formulation for nasal delivery is a very promising preparation with advantages such as rapid and effective absorption, good chemical stability, ease of administration, and minor nasal ciliotoxicity.

Clinical pharmacokinetics of intranasal sumatriptan

A substantial proportion of migraine patients have gastric stasis and suffer severe nausea and/or vomiting during their migraine attack. This may lead to erratic absorption from the gastrointestinal tract and make oral treatment unsatisfactory. For such patients, an intranasal formulation may be advantageous. Sumatriptan is a potent serotonin 5HT(1B/1D) agonist widely used in the treatment of migraine; the effectiveness of the intranasal formulation (20mg) has been well established in several clinical studies. This article reviews the pharmacokinetics of intranasal sumatriptan and includes comparisons with oral and subcutaneous administration. After intranasal administration, sumatriptan is directly and rapidly absorbed, with 60% of the maximum plasma concentration (C(max)) occurring at 30 minutes after administration of a single 20mg dose. Following intranasal administration, approximately 10% more sumatriptan is absorbed probably via the nasal mucosa when compared with oral administration. Mean C(max) after a 20mg intranasal dose is approximately 13.1 to 14.4 ng/mL, with median time to C(max) approximately 1 to 1.75 hours. When given as a single dose, intranasal sumatriptan displays dose proportionality in its extent of absorption and C(max) over the dose range 5 to 10mg, but not between 5 and 20mg for C(max). The elimination phase half-life is approximately 2 hours, consistent with administration by other routes. Sumatriptan is metabolised by monoamine oxidase (MAO; predominantly the A isozyme, MAO-A) to an inactive metabolite. Coadministration with a MAO-A inhibitor, moclobemide, leads to a significant increase in sumatriptan plasma concentrations and is contraindicated. Single-dose pharmacokinetics in paediatric and adolescent patients following intranasal sumatriptan were studied to determine the effect of changes in nasal morphology during growth, and of body size, on pharmacokinetic parameters. The pharmacokinetic profile observed in adults was maintained in the adolescent population; generally, factors such as age, bodyweight or height did not significantly affect the pharmacokinetics. In children below 12 years, C(max) is comparable to that seen in adolescents and adults, but total exposure (area under the concentration-time curve from zero to infinity) was lower in children compared with older patients, especially in younger children treated with 5mg. Clinical experience suggests that intranasal sumatriptan has some advantages over the tablet (more rapid onset of effect and use in patients with gastrointestinal complaints) or subcutaneous (noninvasive and fewer adverse events) formulations.

Inhalation therapy: new delivery systems

The objective of this article is to provide an overview of recent advances in inhalation drug delivery. Problems, advantages, limitations, and developments encountered by different inhalation devices and the agents used in these for the purpose of pulmonary delivery are discussed. A critical appraisal is presented and finally the future directions especially in research of the inhaled therapeutics and aerosols are described.

Intranasal bioavailability of buprenorphine in rabbit correlated to sheep and man

The purpose of the present study of buprenorphine is to add information about the correlation between various animal models and nasal bioavailabilities in man. PEG 300 was added to one formulation to study whether the addition of the co-solvent results in the same absorption pattern as seen for sheep. The bioavailability of intranasal buprenorphine 0.6 mg in PEG 300 and 5% dextrose was assessed in a cross-over study in six rabbits. The mean bioavailabilities, Tmax and Cmax were 46% (S.D. +/-13) and 53% (S.D. +/-17), 8 and 12 min, 28 and 27 ng/ml for 30% PEG 300 and 5% dextrose, respectively. No significant differences were found between the nasal buprenorphine formulations. The bioavailabilities in rabbit and sheep, respectively, were approximately 2.5 and four times higher than for man. The absorption rate was faster for rabbit and sheep than for man. It appears that rabbit and sheep bioavailability differ from humans, especially with respect to rate. PEG 300 do not increase the bioavailability of buprenorphine.

Clearance characteristics of chitosan based formulations in the sheep nasal cavity

This paper describes the clearance characteristics of two bioadhesive nasal delivery systems in the form of chitosan microspheres and chitosan solution, from the nasal cavity of conscious sheep. The pattern of deposition and clearance of the nasal dosage forms were evaluated using a radioactive tracer and the non-invasive technique of gamma scintigraphy. The clearance of chitosan microsphere and solution formulations was compared with that of a control solution. The data show that the control was cleared rapidly from the sheep nasal cavity with a half-time of clearance (time taken for 50% clearance; t(50%)) of about 15 min. The bioadhesive chitosan delivery systems were cleared at a slower rate, with half-times of clearance of 43 min and 115 min, for solution and microsphere formulations respectively. From the results reported in this study it can be concluded that the chitosan delivery systems investigated had significantly reduced rates of clearance from the sheep nasal cavity, as compared to the control. Consequently, chitosan delivery systems have the ability to increase the residence time of drug formulations in the nasal cavity thereby providing the potential for improved systemic medication. The nasal clearance rates recorded in the sheep model mimic very closely the clearance rates found in a previous study using human subjects. It can also be concluded that the sheep can be considered a suitable model for in vivo nasal clearance studies of novel bioadhesive drug delivery systems.

Development and evaluation of nasal formulations of ketorolac

Ketorolac tromethamine is a potent non-narcotic analgesic with moderate anti-inflammatory activity. Clinical studies indicate that ketorolac has a single dose efficacy greater than morphine for postoperative pain and has excellent applicability in the emergency treatment of pain. Due to incomplete oral absorption of ketorolac, several approaches have been tried to develop a nonoral formulation in addition to injections, especially for the treatment of migraine headache. The aim of our study was to develop a nasal formulation of ketorolac with a dose equivalent to the oral formulation. A series of spray and lyophilized powder formulations of ketorolac were administered into the nasal cavity of rabbits, and their pharmacokinetics profiles were assessed. The spray and powder formulations were compared through their pharmacokinetics parameters and absolute bioavailability. Drug plasma concentration was determined using solid phase extraction, followed by an HPLC analysis. Nasal spray formulations were significantly better absorbed than powder formulations. A nasal spray formulation of ketorolac tromethamine showed the highest absorption with an absolute bioavailability of 91%. Within 30 min of administration, the plasma concentration was comparable to that resulting from an intravenous injection. The absolute bioavailability of a solution of ketorolac acid was 70%. Apparently, the dissolution of ketorolac acid into the mucous layer limits its absorption. There were no significant differences in absorption between different powder formulations. Even the reduction of particle size from 123 microm to 63 microm did not indicate better absorption of ketorolac tromethamine from powder formulations. Interestingly, the absolute bioavailability of ketorolac tromethamine from a powder formulation is only 38%, indicating that the drug may not be totally released from the polymer matrix before it is removed from nasal epithelium by mucociliary clearance.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Nasal mucociliary clearance as a factor in nasal drug delivery

The nasal mucociliary clearance system transports the mucus layer that covers the nasal epithelium towards the nasopharynx by ciliary beating. Its function is to protect the respiratory system from damage by inhaled substances. Impairment of nasal mucociliary clearance can result in diseases of the upper airways. Therefore, it is important to study the effects of drugs and drug excipients on nasal mucociliary clearance. A large number of methods are used to assess mucociliary clearance. These methods study the effects of drug and excipients on the mucociliary system in vitro or in vivo in animals and humans. In some cases, the results of different in vitro and in vivo measurements do not correlate well. In vitro methods, especially ciliary beat frequency measurements, have been demonstrated to be valuable tools for toxicity screening. However, in vivo studies are essential to confirm the safety of nasal drug formulations. Nasal mucociliary clearance also has implications for nasal drug absorption. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in fast systemic drug absorption. Several approaches are discussed to increase the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. However, more experimental evidence is needed to support the conclusion that this improved absorption is caused by a longer residence time of the nasal drug formulation.