Nasal Administration: A Tool for Tomorrow's Systemic Administration of Drugs

By its anatomy and physiology, due to the great amount of air treated there, the nasal route represents a very interesting possibility for the administration of products degraded in the gastro-intestinal tract or inhibited by the first hepatic pass. The nasal dosage forms most studied are bioadhesive hydrogels and microspheres, especially for the systemic administration of peptides.     

Nanoneurotherapeutics approach intended for direct nose to brain delivery

Abstract

Context: Brain disorders remain the world's leading cause of disability, and account for more hospitalizations and prolonged care than almost all other diseases combined. The majority of drugs, proteins and peptides do not readily permeate into brain due to the presence of the blood–brain barrier (BBB), thus impeding treatment of these conditions.

Objective: Attention has turned to developing novel and effective delivery systems to provide good bioavailability in the brain.

Methods: Intranasal administration is a non-invasive method of drug delivery that may bypass the BBB, allowing therapeutic substances direct access to the brain. However, intranasal administration produces quite low drug concentrations in the brain due limited nasal mucosal permeability and the harsh nasal cavity environment. Pre-clinical studies using encapsulation of drugs in nanoparticulate systems improved the nose to brain targeting and bioavailability in brain. However, the toxic effects of nanoparticles on brain function are unknown.

Result and conclusion: This review highlights the understanding of several brain diseases and the important pathophysiological mechanisms involved. The review discusses the role of nanotherapeutics in treating brain disorders via nose to brain delivery, the mechanisms of drug absorption across nasal mucosa to the brain, strategies to overcome the blood brain barrier, nanoformulation strategies for enhanced brain targeting via nasal route and neurotoxicity issues of nanoparticles.     

A Simplified Rat Model for Studying Nasal Drug Absorption

Abstract

A simple and rapid rat model for studying nasal drug absorption was developed. In this model, a solution of the test drug, propranolol hydrochloride, was gradually deposited into the nasal cavity of an anesthetized rat through a PE-20 polyethylene catheter connected to a tuberculin syringe via a 30 gauge needle. The extent of drug bioavailability was assessed by measuring propranolol blood levels and the changes in heart rate. For comparative purposes, identical experiments were repeated using the intravenous route of administration, an established rat model requiring surgery, and the proposed model after tracheal cannulation and esophageal li-gation. Although the pharmacokinetic parameters for the various models tested indicated bioavailabilities that were quite similar to that obtained by the intravenous route of administration, the drop in heart rates appeared to be more pronounced with the proposed model than with any of the other two models. In addition to its simplicity, the proposed rat model represents a less stressful and more physiological means of delivering a drug by the nasal route.     

COMPARISON OF NASAL INSULIN POWDERS PREPARED BY SUPERCRITICAL FLUID AND FREEZE-DRYING TECHNIQUES

ABSTRACT

In this study, the effect of drug loading on the nasal absorption of insulin was determined. Human insulin was loaded into different drug carriers by two methods: supercritical fluid processing and freeze-drying. The powder formulations were characterized and then evaluated after nasal administration to alloxan induced diabetic rabbits at a dose of 5U/kg and 7.5U/kg. The blood glucose levels and serum insulin levels were monitored for five hours after administration of insulin formulations. The drug carriers evaluated were: ammonium glycyrrhizinate (AG), polyacrylic acid (PAA), cross-linked polyacrylic acid (CPAA), polyethylene oxide (PEO) and chitosan (CHTN).

Nasal administration of AG infused with insulin by carbon dioxide resulted in absolute bioavailability of 9.81% as compared to 2.86% observed with same powder loaded with insulin by freeze-drying. 8.05% bioavailability was obtained with PAA powder loaded with insulin by carbon dioxide as compared to much lower absorption seen with freeze-dried formulation. Similarly a two fold increase in absolute bioavailability was observed when carbon dioxide infused CPAA powder formulation was compared to the lyophilized powder. Nasal administration of PEO and CHTN loaded with insulin by carbon dioxide resulted in bioavailabilities of 1.55% and 1. 18% respectively.

The drug-loading process seems to have a significant effect on nasal absorption of insulin. The powders loaded with insulin by carbon dioxide infusion resulted in significantly higher absorption. The exact mechanism is still not known and a possible explanation for increased absorption may be due to improved stability of insulin in carbon dioxide infused formulations. Among the powders evaluated, polyacrylic acid and ammonium glycyrrhizinate prepared by carbon dioxide infusion as drug-loading method seem to offer good potential for development of nasal powder dosage forms for insulin.     

Plasma Levels of lormetazepam after Sublingual and Oral Administration of 1 MG to Humans

Abstract

A new galenical formulation containing 1 mg lormeta-zepam (LMZ) for sublingual administration (“sleeping wafer”, see Figure 1) has been developed. In an open-cross over design the plasma lormetazepam levels were monitored radioimmunologically in 16 volunteers. Subjects received the sublingual formulation and an oral tablet (Noctamid^R-1) in a randomized sequence at weekly intervals. After sublingual administration the mean plasma lormetazepam levels were significantly higher between 7.5 and 25 minutes than after administration of the tablet. The earlier rise in plasma LMZ levels is also reflected in partial areas under the plasma level curve up to 45 minutes. LMZ was completely absorbed from both formulations as shown in total AUCs.

It is anticipated that sublingual administration of the new formulation will lead to a 40 - 50 % reduction of sleep latency. Possibilities for therapeutic application of the new formulation are discussed.     

Thermoreversible mucoadhesive in situ nasal gel for treatment of Parkinson’s disease

Abstract

Parkinson’s disease is a degenerative disorder of the central nervous system (CNS). The most obvious symptoms are movement-related such as shaking, rigidity, slowness of movement and difficulty with walking, rigid muscular movements and difficulty in chewing and swallowing especially solid dosage forms. Ropinirole is an anti-Parkinson drug that has low oral bioavailability which is primarily due to first-pass metabolism. The objective of proposed work was to increase bioavailability of ropinirole and avoid patient discomfort by formulating thermoreversible in situ nasal gel. Thermoreversible nasal gels were prepared by cold method using Pluronic F-127 and hydroxy methyl propyl cellulose (HPMC K4M) as gelling agents. Formulations were evaluated for various parameters such as drug content, pH, gelling time, gelling temperature, gel strength, mucoadhesive force, ex vivo diffusion, histological studies and in vivo bioavailability. Formulations displayed gelation at nasal temperature and the gelation time was found to be less than mucociliary clearance time. The nasal residence time was seen to be increased due to mucoadhesion and increased gel strength. The nasal gel formulations showed ex vivo drug release between 56–100% in 5?h. Histological study of sheep nasal mucosa revealed that the gel had a protective effect on the mucosa unlike plain ropinirole which showed evidence of moderate cellular damage. A fivefold increase in bioavailability in brain was observed on nasal administration as compared to IV route. Thermoreversible in situ nasal gel was found to a promising drug delivery for Parkinsonian patients.     

Nanosized nasal emulgel of resveratrol: preparation,optimization, in vitro evaluation and in vivo pharmacokinetic study

Abstract

Nano-emulgel has become one of the most significant controlled release systems, which has the advantages of both gels and nano-emulsions. This work aims at the formulation of nasal nano-emulgel for resveratrol, employing carbopol 934 and poloxamer 407 as the gelling agents. The optimum nano-emulsion was determined through further characterization of the selected system. The nasal nano-emulgel was prepared and tested for the in vitro release, the release kinetics, FTIR, ex vivo permeation, nasal mucosa toxicity, and in vivo pharmacokinetic study. The optimum nano-emulsion consisted of Tween 20, Capryol 90, and Transcutol at a ratio of (54.26: 23.81: 21.93%v/v), and it exhibited transmittance of 100%, resveratrol solubility of 159.9?±?6.4?mg/mL, globule size of 30.65?nm. The in vitro resveratrol released from nano-emulsion and nasal nano-emulgel was 96.17?±?4.43% and 78.53?±?4.7%, respectively. Ex vivo permeation was sustained during 12?h up to 63.95?±?4.7%. The histopathological study demonstrated that the formula is safe and tolerable to the nasal mucosa. C_max and AUC _(0–∞) of resveratrol obtained after nasal administration of nasal nano-emulgel was 2.23 and 8.05 times, respectively. Similarly, T_max was increased up to 3.67?±?0.82?h. The optimized nasal nano-emulgel established intranasal safety and bioavailability enhancement so it is considered as a well-designed system to target the brain.     

Nasal absorption of sulfobromophthalein and amaranth

Abstract

Nasal absorption of sulfobromophthalein (BSP) and amaranth (AM) was investigated and compared with oral absorption in the rat. Bioavailability of BSP and AM after nasal administration was about 26% and 30% respectively. Oral absorption of them was not detected. Nasal route was considered more effective than oral route for these anionic model drugs, but their nasal bioavailability was not so good as expected from the reports for other drugs. High nasal mucus binding of BSP and AM were implied by their high binding to plasma protein (97% and 94%) or to intestinal mucus (78% and 81%). They seemed to have very low lipophilicity since their apparent partition coefficient(APC) between phosphate buffer of various pH and n-octanol were almost zero. They have too large molecular size to pass through the pore (<0.4nm) of nasal mucus membrane. Therefore it was concluded that the low nasal bioavailability of these anionic model drugs might be due to either nonspecific binding to nasal mucus, or low lipophilicity to pass the nasal mucus membrane, or their large molecular size to pass through the pore route of the nasal mucus. Possibility of nasal metabolism in the mucus membrane was excluded since the reported enzymes in the nasal mucus may not affect the metabolism of them.     

Development of a Soluplus budesonide freeze-dried powder for nasal drug delivery

Objective: The aim of this work was to develop an amorphous solid dispersions/solutions (ASD) of a poorly soluble drug, budesonide (BUD) with a novel polymer Soluplus^® (BASF, Germany) using a freeze-drying technique, in order to improve dissolution and absorption through the nasal route.

Significance: The small volume of fluid present in the nasal cavity limits the absorption of a poorly soluble drug. Budesonide is a corticosteroid, practically insoluble and normally administered as a suspension-based nasal spray.

Methods: The formulation was prepared through freeze-drying of polymer-drug solution. The formulation was assessed for its physicochemical (specific surface area, calorimetric analysis and X-ray powder diffraction), release properties and aerodynamic properties as well as transport in vitro using RPMI 2650 nasal cells, in order to elucidate the efficacy of the Soluplus–BUD formulation.

Results: The freeze-dried Soluplus–BUD formulation (LYO) showed a porous structure with a specific surface area of 1.4334?±?0.0178 m²/g. The calorimetric analysis confirmed an interaction between BUD and Soluplus and X-ray powder diffraction the amorphous status of the drug. The freeze-dried formulation (LYO) showed faster release compared to both water-based suspension and dry powder commercial products. Furthermore, a LYO formulation, bulked with calcium carbonate (LYO-Ca), showed suitable aerodynamic characteristics for nasal drug delivery. The permeation across RPMI 2650 nasal cell model was higher compared to a commercial water-based BUD suspension.

Conclusions: Soluplus has been shown to be a promising polymer for the formulation of BUD amorphous solid suspension/solution. This opens up opportunities to develop new formulations of poorly soluble drug for nasal delivery.     

Mechanism of Transdermal Controlled Nitroglycerin Administration (II) Assessment of Rate-Controlling Steps

Abstract

The mechanisms and the rates of skin permeation of nitroglycerin delivered by four transdermal therapeutic systems were investigated using hairless mouse skin mounted on a newly-developed and well-calibrated Keshary-Chien skin permeation system. Experiments were carried out to identify and characterize the rate-controlling roles of stratum corneum, controlled-release drug delivery system and dermal solution sink in the transdermal controlled administration of nitroglycerin.     

Brain targeting of chitosan-based diazepam mucoadhesive microemulsions via nasal route: formulation optimization,characterization, pharmacokinetic and pharmacodynamic evaluation

Objective: The aim of present investigation was to develop microemulsions (MEs) and mucoadhesive microemulsions (MME) of diazepam for brain uptake through nasal administration for the treatment of seizure emergency.

Significance: Status epilepticus (SE) is a medical emergency, requires intravenous administration of diazepam which requires hospitalization of patient. Initiation of therapy at home via nasal administration of diazepam could prevent the damage of brain due to delay of therapy initiation.

Methods: Diazepam MEs were prepared by phase titration method, optimized by using Box–Behnken design. The influence of independent variables oleic acid, surfactant mixture (tween 80:propylene glycol), and water on dependent variables size, flux, and zeta potential was investigated. Optimized MEs, MMEs, and Calmpose (i.v route) were evaluated for pharmacokinetic and pharmacodynamic studies on rats.

Results: MME2 composed of oleic acid (5), surfactant mixture (50), water (45), and chitosan (0.5) showed size of 96.45?nm, PDI 0.21 and zeta potential 13.52?mV. MME2 showed significantly high flux of 846.96?±?34?µg/cm2/h and AUCbrain 1206.49?±?145.8. The drug targeting efficiency (314%) and direct nose-to-brain transport (68.1%) of MME2 were significantly high compared to Calmpose (i.v) and ME. The latency periods of minimal clonal seizures and generalized tonic–clonic seizures of MME2 was significantly increased (p?<?0.0001) compared to drug solution and Calmpose (i.v).

Conclusion: The brain uptake of diazepam from chitosan-based MMEs via nasal route is significantly high compared to i.v route.     

Novel nano-cellulose excipient for generating non-Newtonian droplets for targeted nasal drug delivery

Purpose: Thickening polymers have been used as excipients in nasal formulations to avoid nasal run-off (nasal drip) post-administration. However, increasing the viscosity of the formulation can have a negative impact on the quality of the aerosols generated. Therefore, the study aims to investigate the use of a novel smart nano-cellulose excipient to generate suitable droplets for nasal drug delivery that simultaneously has only marginally increased viscosity while still reducing nasal drips.

Methods: Nasal sprays containing nano-cellulose at different concentrations were investigated for the additive’s potential as an excipient. The formulations were characterized for their rheological and aerosol properties. This was then compared to conventional nasal spray formulation containing the single-component hydroxyl-propyl methyl cellulose (HPMC) viscosity enhancing excipient.

Results: The HPMC-containing nasal formulations behave in a Newtonian manner while the nano-cellulose formulations have a yield stress and shear-thinning properties. At higher excipient concentrations and shear rates, the nano-cellulose solutions have significantly lower viscosities compared to the HPMC solution, resulting in improved droplet formation when actuated through conventional nasal spray.

Conclusions: Nano-cellulose materials could potentially be used as a suitable excipient for nasal drug delivery, producing consistent aerosol droplet size, and enhanced residence time within the nasal cavity with reduced run-offs compared to conventional polymer thickeners.     

Development and gamma-scintigraphy study of Hibiscus rosasinensis polysaccharide-based microspheres for nasal drug delivery

Objective: This work describes the application of natural plant polysaccharide as pharmaceutical mucoadhesive excipients in delivery systems to reduce the clearance rate through nasal cavity.

Methods: Novel natural polysaccharide (Hibiscus rosasinensis)-based mucoadhesive microspheres were prepared by using emulsion crosslinking method for the delivery of rizatriptan benzoate (RB) through nasal route. Mucoadhesive microspheres were characterized for different parameters and nasal clearance of technetium-99m (^99mTc)-radiolabeled microspheres was determined by using gamma-scintigraphy.

Results: Their Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) studies showed that the drug was stable during preparation of microspheres. Aerodynamic diameter of microspheres was in the range 13.23?±?1.83–33.57?±?3.69?µm. Change in drug and polysaccharide ratio influenced the mucoadhesion, encapsulation efficiency and in-vitro release property. Scintigraphs taken at regular interval indicate that control solution was cleared rapidly from nasal cavity, whereas microspheres showed slower clearance (p?Conclusion: Natural polysaccharide-based microspheres achieved extended residence by minimizing effect of mucociliary clearance with opportunity of sustained delivery for longer duration.     

Dry powder nasal drug delivery: challenges,opportunities and a study of the commercial Teijin Puvlizer Rhinocort device and formulation

Purpose: To discuss the challenges and opportunities for dry powder nasal medications and to put this in to perspective by evaluating and characterizing the performance of the Teijin beclomethasone dipropionate (BDP) dry powder nasal inhaler; providing a baseline for future nasal products development.

Methods: The aerosol properties of the formulation and product performance of Teijin powder intranasal spray were assessed, with a particular focus on particle size distribution (laser diffraction), powder formulation composition (confocal Raman microscope) and aerosol performance data (British Pharmacopeia Apparatus E cascade impactor, aerosol laser diffraction).

Results: Teijin Rhinocort^® (BDP) dry powder spray formulation is a simple blend of one active ingredient, BDP with hydroxypropylcellulose (HPC) carrier particles and a smaller quantity of lubricants (stearic acid and magnesium stearate). The properties of the blend are mainly those of the carrier (D_v50?=_?98?±?1.3?µm). Almost the totality of the capsule fill weight (96.5%) was emitted with eight actuations of the device. Using the pharmacopeia suggested nasal chamber deposition apparatus attached to an Apparatus E impactor. The BDP main site of deposition was found to be in the nasal expansion chamber (90.2?±?4.78%), while 4.64?±?1.38% of the BDP emitted dose was deposited on Stage 1 of the Apparatus E.

Conclusions: The Teijin powder nasal device is a simple and robust device to deliver pharmaceutical powder to the nasal cavity, thus highlighting the robustness of intranasal powder delivery systems. The large number of actuations needed to deliver the total dose (eight) should be taken in consideration when compared to aqueous sprays (usually two actuations), since this will impact on patient compliance and consequently therapeutic efficacy of the formulation.     

Design and evaluation of mucoadhesive microemulsion for neuroprotective effect of ibuprofen following intranasal route in the MPTP mice model

Background: The present study is to investigate the neuroprotective effect of ibuprofen by intranasal administration of mucoadhesive microemulsion (MMEI) against inflammation-mediated by dopaminergic neurodegeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson’s disease (PD).

Methods: Ibuprofen-loaded polycarbophil-based MMEI was developed by using response surface methodology (RSM). Ibuprofen with dose of 2.86 mg/kg/day was administered intranasally to male C57BL/6 mice for two consecutive weeks which were pre-treated with four intraperitoneal injections of MPTP (20?mg/kg of body weight) at 2?h intervals. Immunohistochemistry was performed.

Results: Optimal MMEI was stable and non-ciliotoxic with 66.29?±?4.15?nm as average globule size and??20.9?±?3.98?mV as zeta potential. PDI value and transmission electron microscopy result showed the narrow globule size distribution of MMEI. The result showed that all three independent variables had a significant effect (p?<?0.05) on the responses. Rota-rod and open-field test findings revealed the significant improvement in motor performance and gross behavioral activity of the mice. The results from in vivo study and immunohistochemistry showed that nasal administration of Ibuprofen significantly reduced the MPTP-mediated dopamine depletion. Furthermore TH neurons count in the substantia nigra and the density of striatal dopaminergic nerve terminals were found to be significant higher for ibuprofen treated groups.

Conclusion: Findings of the investigation revealed that Ibuprofen through developed MMEI was shown to protect neurons against MPTP-induced injury in the Substantia nigra pars compacta (SNpc) and striatum and hence, could be a promising approach for brain targeting of Ibuprofen through intranasal route to treat PD.     

Ondansetron-loaded chitosan microspheres for nasal antiemetic drug delivery: an alternative approach to oral and parenteral routes

Background: The aim of this study was to develop chitosan microspheres for nasal delivery of ondansetron hydrochloride (OND). Method: Microspheres were prepared with spray-drying method using glutaraldehyde as the crosslinking agent. Microspheres were characterized in terms of morphology, particle size, zeta potential, production yield, drug content, encapsulation efficiency, and in vitro drug release. Results: All microspheres were spherical in shape with smooth surface and positively charged. Microspheres had also high encapsulation efficiency and the suitable particle size for nasal administration. In vitro studies indicated that all crosslinked microspheres had a significant burst effect, and sustained drug release pattern was observed until 24 hours following burst drug release. Nasal absorption of OND from crosslinked chitosan microspheres was evaluated in rats, and pharmacokinetic parameters of OND calculated from nasal microsphere administration were compared with those of both nasal and parenteral administration of aqueous solutions of OND. In vivo data also supported that OND-loaded microspheres were also able to attain a sustained plasma profile and significantly larger area under the curve values with respect to nasal aqueous solution of OND. Conclusion: Based on in vitro and in vivo data, it could be concluded that crosslinked chitosan microspheres are considered as a nasal delivery system of OND.     

Characterization of Dose Delivery and Spray Pattern of a Metered-Dose Flunisolide Nasal Spray

Abstract

Flunisolide is a synthetic fluorinated corticosteroid with significant ant -inflammatory and anti-allergic activities. Flunisolide nasal solution (Nasalide®) is delivered by a unique pump-activated, non-propellant, metered-dose device. A previous paper (1) reported droplet size characterization of the nasal spray by a cascade impactor. This report describes the remaining physical characterizations, namely dose delivery and spray pattern, of this metered-dose delivery system as well as the suitability of the system for a therapeutic corticosteroid nasal solution.

Actuation of flunisolide nasal spray units by 10 subjects over time demonstrated good constancy of dose delivery for up to 24 days of use. The average dose delivery was 0.737 ± 0.040 gm/day (grand mean ± s.d.).

Actuation of similar units by 17 subjects over time showed good constancy of spray pattern, which was defined as the long and short diameters of the impaction pattern of the spray on a TLC plate, for the entire lifetime of the unit.     

Tissue Tolerance of Diclofenac Sodium Encapsulated in Liposomes After Intramuscular Administration

ABSTRACT

In this work the effect of the encapsulation of diclofenac sodium within liposomes on the reduction of the myotoxicity after intramuscular administration in rats was studied. Diclofenac sodium was encapsulated in small unilamellar liposomes obtained from phosphatidylcholine, cholesterol, and α-tocopherol (40:10:0.04 mM), and administered by intramuscular injection in the quadriceps femoral muscle of male Wistar rats. After a single dose of 0.2 mg diclofenac formulations the local tissue damage was assessed by plasma creatine kinase (CPK) activity and histological analysis. It was demonstrated that formulations containing free diclofenac produced a higher increase in CPK activity, while those encapsulated in liposomes exhibited CPK activity similar to the control groups. Histopathological analysis of local muscle tissue performed on the third and seventh days following the injection showed intense cellular damage when free drug solution was used, while encapsulation in liposome protected the tissue against the local tissue inflammation.     

Assessing Lipid Lowering and Plasma Cholesteryl Ester Transfer Protein Activity of Simvastatin Following Administration to Rabbits Fed a High Fat/Cholesterol Diet

ABSTRACT

Purpose: The purpose of this study was to assess the lipid lowering and plasma cholesteryl ester transfer protein (CETP) activity following administration of simvastatin to rabbits fed a high fat/cholesterol diet. Methods: Male New Zealand white rabbits were housed in individual cages and fed a standard diet for 7 days. After 7 days, animals were fed 10 g of a regular chow diet plus 100 g of the same diet supplemented with 0.5% (w/v) cholesterol and 14.0% (w/v) coconut oil for 28 days. Following 28 days on this diet, the animals were randomized based on plasma cholesterol and triglyceride levels, into a group of control animals and a group (n = 6) of animals fed 100 g of cholesterol/coconut diet plus 10 g regular chow diet containing simvastatin (3 mg/kg/day) for an additional 28 days. Blood samples were taken from the marginal ear vein prior to and 28 days after the initiation of drug treatment. Plasma was harvested and stored at 4°C prior to lipid analysis. Plasma total cholesterol and triglyceride levels were quantified using enzymatic kits. HDL (high-density lipoproteins) cholesterol levels were determined using the dextran sulfate-Mg²⁺ precipitation method. ApoB cholesterol levels were determined by subtracting total cholesterol from HDL cholesterol. Cholesteryl ester transfer protein (CETP) activity was determined by standard assay methods. Results: We observed that simvastatin significantly reduced total plasma cholesterol, triglyceride, and apoB cholesterol compared to non-treated controls. Simvastatin treatment did not alter serum CETP activity compared to non-treated controls. Conclusions: These findings suggest that decreasing plasma lipid levels by treatment with simvastatin is not due to changes in serum CETP activity in rabbits fed a high fat/cholesterol diet.     

Influence of Bile Salts on the Permeability Through the Nasal Mucosa of Rabbits of Insulin in Comparison with Dextran Derivatives

Abstract

The nasal drug absorption and the effect of absorption promoters have been studied in rabbits. Nasal mucosa excised from rabbits was mounted as a flat sheet in an in vitro chamber. The result indicates that the change in the porosity of the membrane by pretreatment with bile salts increased the permeability coefficient of sodium chloride in the nasal membrane. The permeabilities of dextran derivatives were enhanced by pretreatment with sodium glycocholate (GC). The permeability coefficient (P) of fluorescein isothiocyanate diethylaminoethyl dextran