Keratin film made of human hair as a nail plate model for studying drug permeation

The limited source of human nail plate for studying drug permeation inspired us to develop a nail plate model made of human hair keratin. The manufacturing process consisted of keratin extraction, dialysis, molding, solvent evaporation, and curing, producing a water-resistant film. The permeability of the film was examined using three markers: sodium fluorescein, rhodamine B, and fluorescein isothiocyanate-dextran as water-soluble, lipid-soluble, and large molecule models, respectively. Bovine hoof was used for comparison. First investigation showed that keratin films (thickness 120 μm) resembled hooves (thickness 100 μm) except that these films were more permeable to rhodamine B compared with hooves (1.8-fold, p < 0.01). Subsequent investigations using ungual penetration enhancers (urea, thioglycolic acid, and papain) showed that keratin films were generally more susceptible than hooves. This study revealed that the produced keratin film offers a possibility as a human nail plate substitute. However, inclusion of the penetration enhancer must be carefully interpreted.     

Triclosan: release from transdermal adhesive formulations and in vitro permeation across human epidermal membranes

Malarial resistance is an escalating global problem and consequently new and more efficacious treatments to combat malaria are urgently needed. The transdermal delivery of anti-malarials may provide an effective alternative or adjunct to conventional regimens. Triclosan is widely used as an anti-bacterial agent and it has recently been demonstrated that this compound has anti-malarial properties. Its high lipophilicity makes it a potential candidate for delivery across the skin and this paper examines in vitro the potential for the transdermal delivery of triclosan from 'drug-in-glue' formulations. Model patches were prepared using DuroTak 2287, 2516 and 2051 acrylic polymer adhesives loaded with 0, 30 and 50 mg per 0.785 cm(-2) triclosan and dissolution was measured over a 12-h period. There was no apparent difference between the adhesives at the 30 mg patch loading, but at 50 mg, the trend for increased release was 2051>2516>2287. No significant burst effect was apparent. Patches of 50 mg per 0.785 cm2 were then used to determine the permeation of triclosan across heat-separated human epidermal membranes in Franz diffusion cells, over a period of 48 h. The above general trend was reflected in the steady state flux values obtained: 2051:16.91 microg x cm(-2) x h(-1) (S.E.M. 1.29), 2516:15.05 microg x cm(-2) x h(-1) (S.E.M. 1.00), 2287 12.83 microg x cm(-2) x h(-1) (S.E.M. 2.81). Although pharmacokinetic data are not currently available to permit calculation of an efficacious patch size, the transdermal delivery of triclosan is feasible.     

Intestinal paracellular permeation enhancement with quaternised chitosan: in situ and in vitro evaluation

Previous studies have shown that N-trimethyl chitosan chloride (TMC) is a potent absorption enhancer for hydrophilic and macromolecular compounds across mucosal surfaces. TMC proved to be effective in neutral and basic pH environments where the absorption enhancing ability of chitosan is severely hampered by its insolubility in these environments. The absorption enhancing characteristics of TMC polymers with different degrees of quaternisation were investigated in vitro and in situ to identify the most effective polymer in a neutral pH environment. Different degrees of quaternisation were obtained by varying the number and duration of the reaction steps in the synthesis process of TMC. The TMC polymers were characterised with 1H-NMR spectroscopy and the degrees of quaternisation were between 22.1 and 48.8%. Everted intestinal sacs (rats) were used to determine the effect of the polymers (0.0625-0.5% w/v) on the permeation of the hydrophilic model compound, [14C]mannitol, at a pH value of 7.4. A single pass intestinal perfusion method was also used to evaluate the permeation enhancing properties of the TMC polymers under the same conditions. The results obtained from both methods clearly showed a pronounced enhancement of [14C]mannitol permeation when administered with the different TMC polymers. It was shown that the permeation enhancing effects depend on the degree of quaternisation of TMC. In both models the best permeation enhancing results were obtained with the highest degree of quaternisation of TMC (48.8%) at a concentration of 0.5% w/v.     

The binding of drugs to different polar lipids in vitro

For evaluation of the physico-chemical basis underlying the drug-induced generalized lipid storage disease, the equilibrium distribution of radioactively labelled amphiphilic drugs between a water phase and liposomes was determined. Liposomes were prepared from sphingomyelin (SM), phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS); the extent of binding of the drugs occurred in increasing order SM ～ PC < PE < PS. A strong correlation was found between the octanol-water partition coefficient and the PC-water coefficient for monovalent cationic drugs; the absolute values of both partition coefficients resembled each other very closely, suggesting that the hydrophobic forces are mainly responsible for the binding of amphiphilic drugs to PC. The higher extent of binding to PS does not result from higher afiinities of the drugs to PS but rather from the higher capacity of PS-liposomes as compared with that of PC- or SM-liposomes. The divalent cationic drug chloroquine displayed particularly high binding to the anionic lipids PS and to gangliosides as compared with the monovalent drugs. This observation might help to explain the ultrastructural and biochemical findings that chloroquine induces a remarkable storage of anionic lipids upon chronic treatment of animals.     

Reaction of drugs with silica surfaces in non polar solvents (author's transl)]

Reaction of Drugs with Silica Surfaces in Non Polar Solvents Infrared spectra were recorded of codeine and benzocaine adsorbed on to colloidal silica Aerosil from CCl₄ solution. Codeine is fixed by hydrogen bonds between silanol groups on the silica surface and the OH-group and the N of the piperidine ring in the organic molecule. The resulting position of the codeine on the surface is confirmed by changes in the C-H-vibration and deformation bands of the drug in the adsorbed state. Hydrogen bonding between benzocaine and the silica surface is caused by the amino groups as proton-donators and the silica surface OH-groups as acceptors. Calculation of the free enthalpy of adsorption from the Langmuir isotherms yielded further evidence on hydrogen bonding of these drugs.     

Evaluation of excised loach skin for studies on transdermal permeation of drugs in vitro

Transdermal permeation of drug across the excised skin of Asian pond loach (Misgurnus anguillicaudatus Cantor) was studied in vitro. Ten kinds of drugs, D-glucose, L-glucose, sucrose, salicylic acid, cefazolin, urea, antipyrine, naphazoline, propranolol and enviomycin were permeated through the excised loach skin, whereas dextran, a polysaccharide, could not be permeated through the skin. The observed transdermal flux (J), the slope of the line obtained from plots of the cumulative amount of drug permeated vs. time, increased as the drug concentration in the donor compartment solution (50----300 mM), as the temperature of the skin (test solution) increased (4----37 degrees C), or as the molecular weight of compound decreased. These results suggested that the transport of drug across the loach skin was due to the passive diffusion mechanism. The effect of pH on the permeation of drug could not be elucidated since the loach skin was drastically impaired below pH 5.0. The J values of antipyrine and naphazoline varied in proportion to the drug concentration in the donor compartment solution at time zero (C0). The permeability constants (Kp, cm.h-1) of antipyrine and naphazoline were 12.9 x 10(-2) and 9.2 x 10(-2), respectively. However, the J values of salicylic acid and urea were not proportional to C0 in high concentration (300 mM). Probably, these results were related to the irritative effect of salicylic acid or urea on the skin.     

Gelucire44/14 as a novel absorption enhancer for drugs with different hydrophilicities: in vitro and in vivo improvement on transcorneal permeation

The objective of this study was to investigate the application of Gelucire44/14 as a novel absorption enhancer in ophthalmic drug delivery system. Six compounds, namely ribavirin, puerarin, mangiferin, berberin hydrochloride, baicalin, and curcumin in the order of increasing lipophilicity were selected as model drugs. The effect of Gelucire44/14 on transcorneal permeation was evaluated across excised rabbit cornea. Ocular irritation and precorneal retention time were assessed. Additionally, aqueous humor pharmacokinetic test was performed by microdialysis. The results indicated that Gelucire44/14, at a concentration of 0.05% or 0.1% (w/v), was found to maximally increase the apparent permeability coefficient by 6.47-, 4.14-, 3.50-, 3.97-, 2.92-, and 1.86-fold for ribavirin, puerarin, mangiferin, berberin hydrochloride, baicalin, and curcumin, respectively (p < 0.05). Moreover, Gelucire44/14 was nonirritant at broad concentrations of 0.025%-0.4% (w/v). Pharmacokinetic tests showed that Gelucire44/14 promoted ocular bioavailability of the compounds as indicated by 5.40-, 4.03-, 3.46-, 3.57-, 2.77-, and 1.77-fold maximal increase in the area under the curve for the drugs aforementioned, respectively (p < 0.01). Therefore, Gelucire44/14 exerted a significant improvement on the permeation of both hydrophilic and lipophilic compounds, especially hydrophilic ones. Hence, Gelucire44/14 can be considered as a safe and effective absorption enhancer for ophthalmic drug delivery system.     

In vitro permeation of several drugs through the human nail plate: relationship between physicochemical properties and nail permeability of drugs.

The objectives of the present study are to clarify the relationship between the physicochemical properties and the nail permeability of drugs through human nail plates. Homologous p-hydroxybenzoic acid esters were used to investigate the relationship between the octanol/water partition coefficient and the permeability coefficient of several drugs. The nail permeability was found to be independent of the lipophilicity of a penetrating drug. However, the nail permeability of several model drugs was found to markedly decrease as their molecular weights increased. The nail permeability of an ionic drug was found to be significantly lower than that of a non-ionic drug, and the nail permeability of these drugs markedly decreased as their molecular weights increased. The permeation of a model drug, 5-fluorouracil (5-FU), through healthy nail plates was also determined and compared with that through nail plates with fungal infections. The drug permeation through a nail plate decreased with an increase in nail plate thickness. Nail plates with fungal infections exhibited approximately the same 5-FU permeation as healthy nail plates. We suggest that the permeability of a drug is mainly influenced by its molecular weight and permeability through nails with fungal infection can be estimated from data on healthy nail permeability.     

Prevalidation of a human cornea construct as an alternative to animal corneas for in vitro drug absorption studies

The use of ophthalmic drugs has increased consistently over the past few decades. Currently, most research is conducted using in vivo and ex vivo animal experiments; however, they have many disadvantages, including ethical concerns, high costs, the questionable extension of animal results to humans, and poor standardization. Although several cell culture-based cornea models have been developed, none have been validated and accepted for general use. In this study, a standardized, three-dimensional model of the human cornea (Hemicornea, HC) based on immortalized human corneal cells and cultivated in serum-free conditions was developed for drug absorption studies and prevalidated using compounds with a wide range of molecular characteristics (sodium fluorescein, rhodamine B, fluorescein isothiocyanate-labeled dextran, aciclovir, bimatoprost, dexamethasone, and timolol maleate). The HC model was independently cultured in three different laboratories, and the intralaboratory and interlaboratory reproducibility was analyzed and compared with the rabbit cornea. This analysis showed that the HC has a barrier in the same range as excised animal corneas, although with a higher reproducibility and lower variability. Because of the demonstrated transferability, the HC represents a promising in vitro alternative to the use of ex vivo tissue and offers a well-defined and standardized system for drug absorption studies.     

盐酸利多卡因纳米高分子脂质体的制备与体外透皮实验研究

【摘要】目的 采用赖氨酸壳聚糖十八烷基季铵盐(OQLCS)/胆固醇包载盐酸利多卡因制备纳米高分子脂质体（LID-PLs）,并研究其体外透皮渗透情况。方法 采用反相蒸发法制备LID-PLs 和盐酸利多卡因传统脂质体 (LID-CLs),用激光粒度仪/Zeta电位仪测试其粒径;建立测定盐酸利多卡因浓度的HPLC法;使用离体小鼠皮和Franz 扩散池进行体外透皮实验,评价不同时间点LID-PLs、LID-CLs和盐酸利多卡因注射液（LID-IJ）的体外透皮渗透情况。结果 LID-PLs组粒径小于LID-CLs组[（61.2±8.14）nm vs（219±7.51）nm]。所建立的HPLC法专一性好,盐酸利多卡因的保留时间为3.899 min,空白纳米高分子脂质体、空白透皮接收液对盐酸利多卡因的测定均无影响,其标准曲线方程为=0.051X-2.701(r = 0.999 9)。LID-PLs组在5 min、10 min、30 min、2 h、4 h、6 h、8 h、12 h及24 h的平均累积透过量均明显高于LID-CLs组和LID-IJ组（P < 0.05或P < 0.01）。LID-CLs组在10 min、30 min、1.5 h、2 h、4 h、6 h、8 h、 12 h、24 h的平均累积透过量均明显高于LID-IJ组（P < 0.05或P < 0.01）。结论 LID-PLs制备简单,具有良好的透皮释放行为,所建立的HPLC方法准确可靠。     

GRGDS-functionalized chitosan nanoparticles as a potential intravenous hemostat for traumatic hemorrhage control in an animal model

Hemostats, which are used for immediate intervention during internal hemorrhage in order to reduce resulting mortality and morbidity, are relatively rare. Here, we describe novel intravenous nanoparticles (CPG-NPs-2000) with chitosan succinate (CSS) as cores, polyethylene glycol (PEG-2000) as spacers and a glycine-arginine-glycine-aspartic acid-serine (GRGDS) peptide as targeted, active hemostatic motifs. CPG-NPs-2000 displayed significant hemostatic efficacy, compared to the saline control, CSS nanoparticles, and tranexamic acid in liver trauma rat models. Further studies have demonstrated that CPG-NPs-2000 are effectively cleared from organs and blood, within 2 and 48?h, respectively. In addition, administration of CPG-NPs-2000 does not affect clotting function under normal physiological conditions, indicating their potential safety in vivo. CPG-NPs-2000 exhibit excellent thermal stability, good solubility, and redistribution ability, in addition to being low cost. These characteristics indicate that CPG-NPs-2000 may have strong potential as effective intravenous hemostats for treating severe internal bleeding.     

Vehicle effects on in vitro skin permeation of and stratum corneum affinity for model drugs caffeine and testosterone

The effects of Labrasol (LBS) (glycolysed ethoxylated C₈/C₁₀ glycerides), Labrafil (LBF) (glycolysed ethoxylated glycerides), Transcutol (TSC) (diethylene glycol monoethyl ether) and DPPG (propylene glycol dipelargonate) on the flux across excised human skin of the lipophilic testosterone (TST) and the hydrophilic caffeine (CAF) and on the affinity of the human stratum corneum for these drugs are compared taking propylene glycol (PG) and liquid petrolatum (LP) as reference vehicles. DPPG and LBF enhance CAF flux relative to PG while LBS and TSC increase the stratum corneum affinity for TST relative to LP. However, the materials tested enhance neither the flux of nor the stratum corneum affinity for both drugs with respect to either reference. On the other hand, a saturated solution of DPPG in PG enhances both properties for both drugs relative to PG. Such effects are ascribed to the ability of DPPG to interact with the lipid bilayers and to that of PG to promote DPPG penetration into stratum corneum and to create interaction sites in such a tissue.     

N-alkylation of highly quaternized chitosan derivatives affects the paracellular permeation enhancement in bronchial epithelia in vitro

This study describes the structure–activity relationship for carefully characterized N-alkyl-N-quaternary chitosan derivatives as permeation enhancers for drugs that are mainly absorbed through the paracellular pathway, such as macromolecular drugs and hydrophilic drugs, in a well defined bronchial epithelial cell line. The O-methyl free derivatives used in the study were fully trimethylated (100%) N,N,N-trimethyl chitosan (TMC) and N-propyl-(QuatPropyl), N-butyl-(QuatButyl) and N-hexyl (QuatHexyl)-N,N-dimethyl chitosan, with 85–91% degree of quaternization. The fully trimethylated TMC, from 0.25 mg/ml, decreased transepithelial electrical resistance (TER) in a reversible manner and enhanced the permeation of the macromolecule FITC–dextran 4 kDa (FD4) 2–5 fold. TMC did not cause any alterations in the tight junction (TJ) protein claudin-4 or in F-actin architecture. QuatHexyl was the most effective polymer to produce enhanced permeation and decreased TER from 0.016 mg/ml. Nevertheless, this enhanced permeation was accompanied by reduced viability and dissociation of F-actin and claudin-4 proteins. The structure–activity relationship suggests that more lipophilic derivatives show more permeation enhancement, TJ disassembly, and less viability in the order of hexyl ≈ butyl > propyl > methyl and demonstrates that the permeation effect is not only mediated by permanent positive charge but also by the extent of N-alkylation. These results are relevant to elucidate the structural factors contributing to the permeation enhancement of chitosan derivatives and for potential use in pulmonary applications.     

In vitro primary human and animal cell-based blood-brain barrier models as a screening tool in drug discovery

Brain penetration is characterized by its extent and rate and is influenced by drug physicochemical properties, plasma exposure, plasma and brain protein binding and BBB permeability. This raises questions related to physiology, interspecies differences and in vitro/in vivo extrapolation. We herein discuss the use of in vitro human and animal BBB model as a tool to improve CNS compound selection. These cell-based BBB models are characterized by low paracellular permeation, well-developed tight junctions and functional efflux transporters. A study of twenty drugs shows similar compound ranking between rat and human models although with a 2-fold higher permeability in rat. cLogP < 5, PSA < 120 ?, MW < 450 were confirmed as essential for CNS drugs. An in vitro/in vivo correlation in rat (R2 = 0.67; P = 2 × 10??) was highlighted when in vitro permeability and efflux were considered together with plasma exposure and free fraction. The cell-based BBB model is suitable to optimize CNS-drug selection, to study interspecies differences and then to support human brain exposure prediction.     

In vitro permeation studies of nanoemulsions containing ketoprofen as a model drug

We prepared a nanoemulsion system with benzyl alcohol/ ethanol/Solutol/smash(R) HS 15 /water. Ketoprofen was used as a model drug in this study. The nanoemulsions of this system evidenced a high degree of stability. The droplet diameter did not change over a period of at least 3 months. The nanoemulsion containing 4% benzyl alcohol evidenced a permeation rate higher than was observed with the 1% and 2% nanoemulsions. Also the nanoemulsion containing 1% Solutol(R) HS 15 provided a permeation rate higher than was seen with the 2% and 4% nanoemulsions. All ketoprofen-loaded nanoemulsions enhanced the in vitro permeation rate through mouse skins as compared to the control.     

N-三甲基壳聚糖对哈西奈德软膏体外促透作用考察

目的：考察取代度为60％的N-三甲基壳聚糖（TMC60）对哈西奈德软膏体外透皮速率的影响。方法：将2％TMC60用于哈西奈德软膏中作为吸收促进剂，并以含2％月桂氮[艹卓]酮的哈西奈德软膏作为阳性对照，以不含任何促渗剂的哈西奈德软膏作为阴性对照，采用Franz扩散池法进行小白鼠离体皮肤渗透实验，HPLC法测定接受液中哈西奈德的含量，计算累积透过量Q，得出Qt回归方程及稳态渗透速率J。结果：哈西奈德线性范围为2．5～75mg·L^-1，回归方程为Y=0．1338＋4．4916X，r=0．9999；回收率为（100．0±0．9）％；日内精密度为1．26％；日间精密度为2．40％。月桂氮[艹卓]酮组和TMC60组的J分别为3．71，3．89（μg·m^-2·h^-1），两者差异无显著性（P＞0．05），而与阴性组相比差异均具有显著性（P＜0．05）。结论：2％TMC60对哈西奈德软膏的体外透皮吸收有较好的促进作用，其作用与2％月桂氮[艹卓]酮相似。     

Cryopreserved primary hepatocytes as a constantly available in vitro model for the evaluation of human and animal drug metabolism and enzyme induction

The use of primary hepatocytes is now well established for both studies of drug metabolism and enzyme induction. Cryopreservation of primary hepatocytes decreases the need for fresh liver tissue. This is especially important for research with human hepatocytes because availability of human liver tissue is limited. In this review, we summarize our research on optimization and validation of cryopreservation techniques. The critical elements for successful cryopreservation of hepatocytes are (1) the freezing protocol, (2) the concentration of the cryoprotectant [10% dimethyl-sulfoxide (DMSO)], (3) slow addition and removal of DMSO, (4) carbogen equilibration during isolation of hepatocytes and before cryopreservation, and (5) removal of unvital hepatocytes by Percoll centrifugation after thawing. Hepatocytes of human, monkey, dog, rat, and mouse isolated and cryopreserved by our standard procedure have a viability > or = 80%. Metabolic capacity of cryopreserved hepatocytes determined by testosterone hydroxylation, 7-ethoxyresorufin-O-de-ethylase (EROD), 7-ethoxycoumarin-O-deethylase (ECOD), glutathione S-transferase, UDP-glucuronosyl transferase, sulfotransferase, and epoxide hydrolase activities is > or = 60% of freshly isolated cells. Cryopreserved hepatocytes in suspension were successfully applied in short-term metabolism studies and as a metabolizing system in mutagenicity investigations. For instance, the complex pattern of benzo[a]pyrene metabolites including phase II metabolites formed by freshly isolated and cryopreserved hepatocytes was almost identical. For the study of enzyme induction, a longer time period and therefore cryopreserved hepatocyte cultures are required. We present a technique with cryopreserved hepatocytes that allows the induction of testosterone metabolism with similar induction factors as for fresh cultures. However, enzyme activities of induced hepatocytes and solvent controls were smaller in the cryopreserved cells. In conclusion, cryopreserved hepatocytes held in suspension can be recommended for short-term metabolism or toxicity studies. Systems with cryopreserved hepatocyte cultures that could be applied for studies of enzyme induction are already in a state allowing practical application, but may be further optimized.     

Evaluation of human serum albumin as a substitute of foetal bovine serum for cell culture

Cell microencapsulation requires clinically approved materials for their use in pharmaceutical and/or biomedical applications. The overwhelming majority of the literature has used the classical alginate-poly-l-lysine-alginate (APA) capsules for cell immobilization. Although alginate is granted with the medical approval, some of the remaining components such as foetal bovine serum (FBS), an essential ingredient of cell culture media, are not in accordance with the guidelines affirmed by the American Society for Testing and Materials (ASTM) and Food and Drug Administration (FDA). In this paper, human serum albumin (HSA), a medically approved substance, was evaluated as a potential substitute of FBS. The effect of different percentages of FBS and HSA was studied on the proliferation rate, viability and protein production of two different cell lines (C2C12 and baby hamster kidney (BHK) cells), maintained in culture and immobilized in APA microcapsules. Results show that substitution of FBS by HSA reduced the functionality of both non-encapsulated and encapsulated BHK cells. However, immobilized C2C12 cells presented the highest level of viability and a reduction in protein production of 25% when 1% HSA was used. It can be concluded that HSA might be a possible substitute of FBS in order to maintain or transport encapsulated C2C12 cells for short periods of time before implantation.     

Use of the biodegradable polymer chitosan as a vehicle for applying drugs to the inner ear

Development of efficient local delivery systems for the auditory organ has an important role in clinical practice for the management of inner ear disorders using pharmacological means. Chitosan, a biodegradable polymer, is a good drug carrier with bioadhesive properties. The aim of this study was to investigate the feasibility of using chitosan to deliver drugs to the inner ear across the round window membrane (RWM).Three structurally different chitosans loaded with a tracer drug, neomycin, were injected into the middle ear cavity of albino guinea pigs (n = 35). After 7 days the effect of chitosans and neomycin was compared among the treatment groups. The hearing organ was analysed for hair cell loss and the RWM evaluated in term of thickness.All tested chitosan formulations successfully released the loaded neomycin which then diffused across the RWM, and exerted ototoxic effect on the cochlear hair cells in a degree depending on the concentrations used. Chitosans per se had no noxious effect on the cochlear hair cells. It is concluded that the chitosans, and especially glycosylated derivative, are safe and effective carriers for inner ear therapy.     

Microemulsion-based delivery of triamcinolone acetonide to posterior segment of eye using chitosan and butter oil as permeation enhancer: an in vitro and in vivo investigation

The aim of the study was to formulate a microemulsion (ME) using chitosan (CH) and the butter oil (BO) as a permeation enhancer for targeting drug to the posterior segment of the eye, via topical route. Triamcinolone acetonide (TA) was selected as the model drug since it undergoes extensive first-pass metabolism, leading to poor oral bioavailability of 23%. For optimisation of BO concentration, different ratios of TA:BO were prepared by simple physical mixing in the ratio of 1:9 to 9:1 and diffusion study was performed. MEs containing TA, TA:BO and TA CH ME were formulated by water titration method. Globule sizes of TA ME, TA:BO ME and TA CH ME were found to be 66.06?±?0.32?nm, 78.52?±?1.50?nm and 97.30?±?2.50?nm, respectively. In ex vivo diffusion studies using goats eye, TA:BO ME (31.33?±?0.46 and 33.98?±?0.23) and TA CH ME (24.10?±?0.41 and 27.00?±?0.18) showed higher percentage of drug diffusion in comparison to TA ME (13.29?±?0.41and 15.56?±?0.34) and TA solution (8.20?±?1.04 and 10.39?±?0.22) in presence and in absence of vitreous humour. Fluorescence intensity of coumarin-6 (as a marker) loaded ME with BO and CH was found to be higher, confirming their role in altering membrane permeability and facilitating coumarin-6 diffusion to the posterior chamber. Overall, it was concluded that BO enhances the bioavailability of TA across the retina, thereby proving its potential as permeation enhancer in facilitating drug delivery to the posterior segment of the eye.