Delivery of gatifloxacin using microemulsion as vehicle: formulation, evaluation, transcorneal permeation and aqueous humor drug determination

Breaking Barriers: Nanomedicine-Based Drug Delivery for Cataract Treatment

Cataract is a leading cause of blindness globally, and its surgical treatment poses a significant burden on global healthcare. Pharmacologic therapies, including antioxidants and protein aggregation reversal agents, have attracted great attention in the treatment of cataracts in recent years. Due to the anatomical and physiological barriers of the eye, the effectiveness of traditional eye drops for delivering drugs topically to the lens is hindered. The advancements in nanomedicine present novel and promising strategies for addressing challenges in drug delivery to the lens, including the development of nanoparticle formulations that can improve drug penetration into the anterior segment and enable sustained release of medications. This review introduces various cutting-edge drug delivery systems for cataract treatment, highlighting their physicochemical properties and surface engineering for optimal design, thus providing impetus for further innovative research and potential clinical applications of anti-cataract drugs.

Sustained release gel (polymer-free) of itraconazole-loaded microemulsion for oral candidiasis treatment: time-kill kinetics and cellular uptake

Itraconazole (ICZ) was prepared in a self-microemulsifying (SM) gel. This gel was intended for use in the oral mucosa, where low volume and flow of saliva result in limited solubility and absorption of drugs that are poorly water-soluble. The drug-loaded gel formulation (ICZ-SM) was selected as a clear solution in the ternary phase diagram to improve the solubility of ICZ. Seven ratios (S1-S7) were prepared by mixing polyoxyl 35 castor oils (P35), a medium chain with a blend of mono-, di-, and triglycerides (MCT), and water. Phase separation of large-sized emulsions by countering with artificial saliva were observed in dilution tests for the formulation contained MCT, P35, and water at the ratios of 70:20:10 (S1), 10:80:10 (S3), and 20:60:20 (S4). Formulations in the ratios of 15:50:35 (S5) and 19:43:38 (S6) produced strong ICZ-SM gels, as shown by rheology tests, whereas the formulations at the ratios of 30:60:10 (S2) and 10:43:47 (S7) exhibited no elasticity. A model of zero-order kinetic (S5) and first-order kinetic (S6) were found to best fit the release kinetics of ICZ from the gels. Time-killing assays revealed that S5 and S6 required less time compared with S2 and the ICZ solution. Furthermore, S5 exhibited the highest increase in cell uptake compared with S2, S6, and the ICZ solution. These findings suggest that the ICZ-SM gel was a free polymer capable of delivering an ICZ for the treatment of oral candidiasis, and that ICZ-SM gels applied locally exhibit enhanced absorption into cells.

Development of Osthole-Loaded Microemulsions as a Prospective Ocular Delivery System for the Treatment of Corneal Neovascularization: In Vitro and In Vivo Assessments

Osthole (OST), a natural coumarin compound, has shown a significant inhibitory effect on corneal neovascularization (CNV). But, its effect on treating CNV is restricted by its water insolubility. To overcome this limitation, an OST-loaded microemulsion (OST-ME) was created to improve the drug's therapeutic effect on CNV after topical administration. The OST-ME formulation comprised Capryol-90 (CP-90), Cremophor® EL (EL-35), Transcutol-P (TSP) and water, and sodium hyaluronate (SH) was also included to increase viscosity. The OST-ME had a droplet size of 16.18 ± 0.02 nm and a low polydispersity index (0.09 ± 0.00). In vitro drug release from OST-ME fitted well to the Higuchi release kinetics model. Cytotoxicity assays demonstrated that OST-ME was not notably toxic to human corneal epithelial cells (HCECs), and the formulation had no irritation to rabbit eyes. Ocular pharmacokinetics studies showed that the areas under the concentration-time curves (AUC0-t) in the cornea and conjunctiva were 19.74 and 63.96 μg/g*min after the administration of OST-ME, both of which were 28.2- and 102.34-fold higher than those after the administration of OST suspension (OST-Susp). Moreover, OST-ME (0.1%) presented a similar therapeutic effect to commercially available dexamethasone eye drops (0.025%) on CNV in mouse models. In conclusion, the optimized OST-ME exhibited good tolerance and enhanced 28.2- and 102.34-fold bioavailability in the cornea and conjunctiva tissues compared with suspensions in rabbit eyes. The OST-ME is a potential ocular drug delivery for anti-CNV.

Topical Sustained-Release Dexamethasone-Loaded Chitosan Nanoparticles: Assessment of Drug Delivery Efficiency in a Rabbit Model of Endotoxin-Induced Uveitis

Uveitis is an ocular illness that if not treated properly can lead to a total loss of vision. In this study, we evaluated the utility of HA-coated Dexamethasone-sodium-phosphate (DEX)-chitosan nanoparticles (CSNPs) coated with hyaluronic acid (HA) as a sustained ocular delivery vehicle for the treatment of endotoxin-induced-uveitis (EIU) in rabbits. The CSNPs were characterized for particle size, zeta potential, polydispersity, surface morphology, and physicochemical properties. Drug encapsulation, in vitro drug release, and transcorneal permeation were also evaluated. Finally, eye irritation, ocular pharmacokinetics, and pharmacodynamics were in vivo. The CSNPs ranged from 310.4 nm and 379.3 nm pre-(uncoated) and post-lyophilization (with HA-coated), respectively. The zeta potentials were +32 mV (uncoated) and -5 mV (HA-uncoated), while polydispersity was 0.178-0.427. Drug encapsulation and loading in the CSNPs were 73.56% and 6.94% (uncoated) and 71.07% and 5.54% (HA-coated), respectively. The in vitro DEX release over 12 h was 77.1% from the HA-coated and 74.2% from the uncoated NPs. The physicochemical properties of the CSNPs were stable over a 3-month period when stored at 25 °C. Around a 10-fold increased transcorneal-flux and permeability of DEX was found with HA-CSNPs compared to the DEX-aqueous solution (DEX-AqS), and the eye-irritation experiment indicated its ocular safety. After the ocular application of the CSNPs, DEX was detected in the aqueous humor (AH) till 24 h. The area under the concentrations curve (AUC0-24h) for DEX from the CSNPs was 1.87-fold (uncoated) and 2.36-fold (HA-coated) higher than DEX-AqS. The half-life (t1/2) of DEX from the uncoated and HA-coated NPs was 2.49-and 3.36-fold higher, and the ocular MRT0-inf was 2.47- and 3.15-fold greater, than that of DEX-AqS, respectively. The EIU rabbit model showed increased levels of MPO, TNF-α, and IL-6 in AH. Topical DEX-loaded CSNPs reduced MPO, TNF-α, and IL-6 levels as well as inhibited NF-κB expression. Our findings demonstrate that the DEX-CSNPs platform has improved the delivery properties and, hence, the promising anti-inflammatory effects on EIU in rabbits.

Preparation of a Sunitinib loaded microemulsion for ocular delivery and evaluation for the treatment of corneal neovascularization in vitro and in vivo

Background: Corneal neovascularization (CNV) is a pathological condition that can disrupt corneal transparency, thus harming visual acuity. However, there is no effective drug to treat CNV. Sunitinib (STB), a small-molecule multiple receptor tyrosine kinase inhibitor, was shown to have an effect on CNV. The purpose of this study was to develop an STB microemulsion (STB-ME) eye drop to inhibit CNV by topical application. Methods: We successfully prepared an STB-ME by the phase inversion emulsification method, and the physicochemical properties of STB-MEs were investigated. The short-term storage stability, cytotoxicity to human corneal epithelial cells, drug release, ocular irritation, ocular pharmacokinetics and the inhibitory effect on CNV were evaluated in vitro and in vivo. Results: The optimal formulation of STB-ME is composed of oleic acid, CRH 40, Transcutol P, water and sodium hyaluronate (SH). It is a uniform spherical particle with a mean droplet size of 18.74 ± 0.09 nm and a polydispersity index of 0.196 ± 0.004. In the in vitro drug release results, STB-ME showed sustained release and was best fitted by a Korsmeyer-Peppas model (R ² = 0.9960). The results of the ocular pharmacokinetics in rabbits showed that the formulation containing SH increased the bioavailability in the cornea (2.47-fold) and conjunctiva (2.14-fold). STB-ME (0.05% and 0.1%), administered topically, suppressed alkali burn-induced CNV in mice more effectively than saline, and high-dose (0.1%) STB-ME had similar efficacy to dexamethasone (0.025%). Conclusion: This study provides a promising formulation of STB-ME for the inhibition of CNV by topical administration, which has the excellent characteristics of effectiveness, sustained release and high ocular bioavailability.

Nanocarriers significantly augment the absorption of ocular-delivered drugs: A comparative meta-analysis study

This study presents a meta-analysis that compiles information collected from several studies aiming to prove, by evidence, that nanocarriers out-perform conventional formulations in augmenting the bioavailability of ocular topically administered drugs. Data was further categorized into two subgroups; polymeric-based nanocarriers versus their lipid-based counterparts, as well as, naturally-driven carriers versus synthetically-fabricated ones. After normalization, the pharmacokinetic factor, area under the curve (AUC), was denoted as the "effect" in the conducted study, and the corresponding Forest plots were obtained. Our meta-analysis study confirmed the absorption enhancement effect of loading drugs into nanocarriers as compared to conventional topical ocular dosage forms. Interestingly, no significant differences were recorded between the polymeric and lipidic nanocarriers included in the study, while naturally-driven nanoplatforms were proven superior to the synthetic alternatives.

Ophthalmic nano-bioconjugates: critical challenges and technological advances

Ophthalmic disease can cause permanent loss of vision and blindness. Easy-to-administer topical and systemic treatments are preferred for treating sight-threatening disorders. Typical ocular anatomy makes topical and systemic ophthalmic drug delivery challenging. Various novel nano-drug delivery approaches are developed to attain the desired bioavailability in the eye by increasing residence time and improved permeability across the cornea. The review focuses on novel methods that are biocompatible, safe and highly therapeutic. Novelty in nanocarrier design and modification can overcome their drawbacks and make them potential drug carriers for eye disorders in both the anterior and posterior eye segments. This review briefly discussed technologies, patented developments, and clinical trial data to support nanocarriers' use in ocular drug delivery.

Biopolymers in Mucoadhesive Eye Drops for Treatment of Dry Eye and Allergic Conditions: Application and Perspectives

Dry eye syndrome and allergic conjunctivitis are the most common inflammatory disorders of the eye surface. Although eye drops are the most usual prescribed dosage form, they are characterized by low ocular availability due to numerous barrier mechanisms of the eye. The use of biopolymers in liquid ophthalmic preparations has numerous advantages, such as increasing the viscosity of the tear film, exhibiting bioadhesive properties, and resisting the drainage system, leading to prolonged retention of the preparation at the site of application, and improvement of the therapeutic effect. Some mucoadhesive polymers are multifunctional excipients, so they act by different mechanisms on increasing the permeability of the cornea. Additionally, many hydrophilic biopolymers can also represent the active substances in artificial tear preparations, due to their lubrication and moisturizing effect. With the modification of conventional ophthalmic preparations, there is a need for development of new methods for their characterization. Numerous methods for the assessment of mucoadhesiveness have been suggested by the literature. This review gives an overview related to the development of mucoadhesive liquid ophthalmic formulations for the treatment of dry eye and allergic conditions.

Modeling the Endothelial Glycocalyx Layer in the Human Conventional Aqueous Outflow Pathway

A layer of proteoglycans and glycoproteins known as glycocalyx covers the surface of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm's canal (SC) inner wall of the conventional aqueous outflow pathway in the eye. This has been shown to play a role in the mechanotransduction of fluid shear stress and in the regulation of the outflow resistance. The outflow resistance in the conventional outflow pathway is the main determinant of the intraocular pressure (IOP) through an active, two-way, fluid-structure interaction coupling between the outflow tissues and aqueous humor. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex with interspersed aqueous humor was constructed. A very thin charged double layer that represents the endothelial glycocalyx layer covered the surface of the elastic outflow tissues. The aqueous humor was modeled as electroosmotic flow that is charged when it is in contact with the outflow tissues. The electrical-fluid-structure interaction (EFSI) method was used to couple the charged double layer (glycocalyx), fluid (aqueous humor), and solid (outflow tissues). When the IOP was elevated to 15 mmHg, the maximum aqueous humor velocity in the EFSI model was decreased by 2.35 mm/s (9%) compared to the fluid-structure interaction (FSI) model. The charge or electricity in the living human conventional outflow pathway generated by the charged endothelial glycocalyx layer plays a minor biomechanical role in the resultant stresses and strains as well as the hydrodynamics of the aqueous humor.

Promotional effect of Ca doping on Bi2Fe4O9 as peroxymonosulfate activator for gatifloxacin removal

A series of Ca-doped bismuth ferrite was prepared at various %w/w of Ca via a facile hydrothermal method to obtain Bi_2XCa_2(1-X)Fe₄O₉ (denoted as BFOCa-X, where X = 1, 0.95, 0.90, 0.80, 0.50). The BFOCa-X catalysts were characterized, and the results showed that they consist of pure phase BFO with nanosheet-like morphology. The as-prepared BFOCa-X catalysts were used as peroxymonosulfate (PMS) activator for gatifloxacin (GAT) removal. It was found that the catalytic activity decreased in the following order: BFOCa-0.8 (90.2% GAT removal efficiency in 45 min, k_app = 0.084 min^-1)>BFOCa-0.95 > BFOCa-0.9 > BFOCa-0.5 > BFO indicating that BFOCa-0.8 has the optimized active sites for catalysis. The Ca dopant contributed to the increased oxygen vacancies and surface hydroxyl groups, promoting the catalytic PMS activation process. The k_app value increased gradually with increasing catalyst loading and PMS dosage while pH 9 presented the highest GAT removal rate. The GAT degradation rate was inhibited by PO₄³-, humic acid and NH₄⁺ but promoted in the presence of Cl-, NO₃- and HCO₃-. It was also found that the GAT can undergo several degradation pathways in the catalytic PMS system, which eventually mineralized into innocuous compounds. The dominant reactive oxygen species (ROS) were identified using chemical scavengers, revealing that SO₄^•-, ¹O₂ and ^•OH contributed significantly to GAT degradation. Based on the XPS study, PMS was activated by the Fe²⁺/Fe³⁺ redox cycling and oxygen vacancies to produce SO₄^•-/^•OH and ¹O₂, respectively. Overall, the BFOCa-0.8 also showed excellent reusability up to at least 4 cycles with low Bi and Fe leaching (<7 and 62 μg L^-1, respectively), indicating that it has promising potential for application as PMS activator for antibiotics removal.

An Update on Novel Ocular Nanosystems with Possible Benefits in the Treatment of Corneal Neovascularization

Corneal neovascularization (CNV) is an ocular pathological change that results from an imbalance between angiogenic factors and antiangiogenic factors as a result of various ocular insults, including infection, inflammation, hypoxia, trauma, corneal degeneration, and corneal transplantation. Current clinical strategies for the treatment of CNV include pharmacological treatment and surgical intervention. Despite some degree of success, the current treatment strategies are restricted by limited efficacy, adverse effects, and a short duration of action. Recently, gene-based antiangiogenic therapy has become an emerging strategy that has attracted considerable interest. However, potential complications with the use of viral vectors, such as potential genotoxicity resulting from long-term expression and nonspecific targeting, cannot be ignored. The use of ocular nanosystems (ONS) based on nanotechnology has emerged as a great advantage in ocular disease treatment during the last two decades. The potential functions of ONS range from nanocarriers, which deliver drugs and genes to target sites in the eye, to therapeutic agents themselves. Various preclinical studies conducted to date have demonstrated promising results of the use of ONS in the treatment of CNV. In this review, we provide an overview of CNV and its current therapeutic strategies and summarize the properties and applications of various ONS related to the treatment of CNV reported to date. Our goal is to provide a comprehensive review of these considerable advances in ONS in the field of CNV therapy over the past two decades to fill the gaps in previous related reports. Finally, we discuss existing challenges and future perspectives of the use of ONS in CNV therapy, with the goal of providing a theoretical contribution to facilitate future practical growth in the area.

Advances in ophthalmic drug delivery technology for postoperative management after cataract surgery

INTRODUCTION

Cataract surgery is becoming more common due to an aging world population. Intraocular lenses and surgical technique have developed remarkably recently, but the development of postoperative medication to prevent postsurgery complications has been relatively delayed. We still largely depend on eye drops for the management of post-cataract-surgery patients. Mental and physical problems that often occur in elderly cataract patients make it difficult for patients to apply eye drops by themselves. It is necessary to develop new effective drug delivery methods.

AREAS COVERED

This updated review article provides a brief review of why drug management is needed following cataract surgery and an overview of current developments in new drug delivery methods for ophthalmic treatment. In particular, various novel drug delivery methods that can be used for post-cataract-surgery management and their current development stages are extensively reviewed.

EXPERT OPINION

Rapidly developing technologies, such as intraocular and external ophthalmic implants, polymers, and nanotechnology, are being actively applied to develop novel drug delivery systems for safe and effective management after cataract surgery. Their goal is to achieve sufficient drug release for the desired duration with a single application. These will largely replace the inconvenience of eye drops for elderly patients in the future.

Perspectives of Positively Charged Nanocrystals of Tedizolid Phosphate as a Topical Ocular Application in Rabbits

The aim of this study was the successful utilization of the positively charged nanocrystals (NCs) of Tedizolid Phosphate (TZP) (0.1% w/v) for topical ocular applications. TZP belongs to the 1, 3-oxazolidine-2-one class of antibiotics and has therapeutic potential for the treatment of many drug-resistant bacterial infections, including eye infections caused by MRSA, penicillin-resistant Streptococcus pneumonia and vancomycin-resistant Enterococcus faecium. However, its therapeutic usage is restricted due to its poor aqueous solubility and limited ocular availability. It is a prodrug and gets converted to Tedizolid (TDZ) by phosphatases in vivo. The sterilized NC₁ was subjected to antimicrobial testing on Gram-positive bacteria. Ocular irritation and pharmacokinetics were performed in rabbits. Around a 1.29 to 1.53-fold increase in antibacterial activity was noted for NC₁ against the B. subtilis, S. pneumonia, S. aureus and MRSA (SA-6538) as compared to the TZP-pure. The NC₁-AqS was “practically non-irritating” to rabbit eyes. There was around a 1.67- and 1.43 fold increase in t_1/2 (h) and C_max (ngmL⁻¹) while there were 1.96-, 1.91-, 2.69- and 1.41-times increases in AUC_0–24h,AUC_0–∞,AUMC_0–∞ and MRT_0–∞, respectively, which were found by NC₁ as compared to TZP-AqS in the ocular pharmacokinetic study. The clearance of TDZ was faster (11.43 mLh⁻¹) from TZP-AqS as compared to NC₁ (5.88 mLh⁻¹). Relatively, an extended half-life (t_1/2; 4.45 h) of TDZ and the prolonged ocular retention (MRT_0–∞; 7.13 h) of NC₁ was found, while a shorter half-life (t_1/2; 2.66 h) of TDZ and MRT_0–∞(t_1/2; 5.05 h)was noted for TZP-AqS, respectively. Cationic TZP-NC₁ could offer increased transcorneal permeation, which could mimic the improved ocular bioavailability of the drug in vivo. Conclusively, NC₁ of TZP was identified as a promising substitute for the ocular delivery of TZP, with better performance as compared to its conventional AqS.

Novel Eye Drop Delivery Systems: Advance on Formulation Design Strategies Targeting Anterior and Posterior Segments of the Eye

Eye drops are the most common and convenient route of topical administration and the first choice of treatment for many ocular diseases. However, the ocular bioavailability of traditional eye drops (i.e., solutions, suspensions, and ointments) is very low because of ophthalmic physiology and barriers, which greatly limits their therapeutic effect. Over the past few decades, many novel eye drop delivery systems, such as prodrugs, cyclodextrins, in situ gels, and nanoparticles, have been developed to improve ophthalmic bioavailability. These novel eye drop delivery systems have good biocompatibility, adhesion, and propermeation properties and have shown superior performance and efficacy over traditional eye drops. Therefore, the purpose of this review was to systematically present the research progress on novel eye drop delivery systems and provide a reference for the development of dosage form, clinical application, and commercial transformation of eye drops.

Polyaphron Formulations Stabilised with Different Water-Soluble Polymers for Ocular Drug Delivery

As drug delivery to the eye has evolved over the last decades, researchers have explored more effective treatments for ocular diseases. Despite this, delivering drugs to the cornea remains one of the most problematic issues in ophthalmology due to the poor permeability of the cornea and tear clearance mechanisms. In this study, four different types of polyaphron formulations are prepared with 10% poloxamer 188 (P188), 10% poly(2-ethyl-2-oxazoline), 1% polyquaternium 10, and 3% sodium carboxymethylcellulose solutions mixed with 1% Brij® L4 in a caprylic/capric triglycerides solution. Their physicochemical characteristics, rheological properties, and stability are assessed. Additionally, a polyaphron with 3% polyquaternium 10 was prepared for the assessment of ex vivo corneal retention along with four other polyaphrons. The best retention on the ex vivo cornea was displayed by the 3% polyquaternium 10-based formulation. The 10% poloxamer 188 along with 1% polyquaternium 10-based polyaphrons appeared to be the most stable among the four prepared formulations. A toxicological evaluation of these formulations was performed using a slug mucosal irritation test and bovine corneal opacity and permeability assay, with all four polyaphrons proving good biocompatibility with ocular tissues. The developed drug delivery systems demonstrated an excellent potential for ocular drug delivery.

Sorafenib-loaded nanostructured lipid carriers for topical ocular therapy of corneal neovascularization: development, in-vitro and in vivo study

Sorafenib (SRB), a multikinase inhibitor, is effective in reducing experimental corneal neovascularization (CNV) after oral administration; however, its therapeutic use in ocular surface disorders is restricted due to poor solubility and limited bioavailability. This study aimed to develop and optimize SRB-loaded nanostructured lipid carriers (SRB-NLCs) for topical ocular delivery by a central composite design response surface methodology (CCD-RSM). It was spherical and uniform in morphology with an average particle size of 111.87 ± 0.93 nm and a narrow size distribution. The in vitro drug release from the released SRB-NLC formulation was well fitted to Korsmeyer Peppas release kinetics. The cell counting kit-8 (CCK-8) cell viability assay demonstrated that SRB-NLC was not obviously cytotoxic to human corneal epithelial cells (HCECs). An in vivo ocular irritation test showed that SRB-NLC was well tolerated by rabbit eyes. Ocular pharmacokinetics revealed 6.79-fold and 1.24-fold increase in the area under concentration-time curves (AUC_0-12h) over 12 h in rabbit cornea and conjunctiva, respectively, treated with one dose of SRB-NLC compared with those treated with SRB suspension. Moreover, SRB-NLC (0.05% SRB) and dexamethasone (0.025%) similarly suppressed corneal neovascularization in mice. In conclusion, the optimized SRB-NLC formulation demonstrated excellent physicochemical properties and good tolerance, sustained release, and enhanced ocular bioavailability. It is safe and potentially effective for the treatment of corneal neovascularization.

Drug Delivery Challenges and Current Progress in Nanocarrier-Based Ocular Therapeutic System

Drug instillation via a topical route is preferred since it is desirable and convenient due to the noninvasive and easy drug access to different segments of the eye for the treatment of ocular ailments. The low dose, rapid onset of action, low or no toxicity to the local tissues, and constrained systemic outreach are more prevalent in this route. The majority of ophthalmic preparations in the market are available as conventional eye drops, which rendered <5% of a drug instilled in the eye. The poor drug availability in ocular tissue may be attributed to the physiological barriers associated with the cornea, conjunctiva, lachrymal drainage, tear turnover, blood–retinal barrier, enzymatic drug degradation, and reflex action, thus impeding deeper drug penetration in the ocular cavity, including the posterior segment. The static barriers in the eye are composed of the sclera, cornea, retina, and blood–retinal barrier, whereas the dynamic barriers, referred to as the conjunctival and choroidal blood flow, tear dilution, and lymphatic clearance, critically impact the bioavailability of drugs. To circumvent such barriers, the rational design of the ocular therapeutic system indeed required enriching the drug holding time and the deeper permeation of the drug, which overall improve the bioavailability of the drug in the ocular tissue. This review provides a brief insight into the structural components of the eye as well as the therapeutic challenges and current developments in the arena of the ocular therapeutic system, based on novel drug delivery systems such as nanomicelles, nanoparticles (NPs), nanosuspensions, liposomes, in situ gel, dendrimers, contact lenses, implants, and microneedles. These nanotechnology platforms generously evolved to overwhelm the troubles associated with the physiological barriers in the ocular route. The controlled-drug-formulation-based strategic approach has considerable potential to enrich drug concentration in a specific area of the eye.

Targeting Ocular Drug Delivery: An Examination of Local Anatomy and Current Approaches

Ocular drug delivery remains the focus of much modern research. Primary routes of administration include the surface, the intravitreal space, the subretinal space, and the subconjunctival space, each with its own series of unique challenges, limitations, and advantages. Each of these approaches requires careful consideration of the local anatomy, physical barriers, and key cells as well as the interface between the anatomy and the drug or drug system being delivered. While least invasive, the topical route poses a challenge with the many physical barriers that prevent drug penetration into the eye; while injection into the intravitreal, subretinal, and subconjunctival spaces are direct and targeted but limited due to the many internal clearance mechanisms and potential for damage to the eye. Polymeric-based, sustained-release drug delivery systems have been identified as a potential solution to many of these challenges; however, the design and successful implementation of a sustained-release system that is well-tolerated, bioactive, biocompatible, and degradable remains, in many cases, only in the early stages. The drugs and biomaterials in question also require special attention as small chemical changes could result in vastly different outcomes. This paper explores the anatomy and key cells of these four primary drug delivery routes as well as the interface between drug and drug delivery systems and the anatomy, reviewing the recent developments and current state of research in each area. Finally, this paper also examines the frequently used drugs and biomaterials found in ocular drug delivery and summarizes the primary interactions observed.

Development of a naringenin microemulsion as a prospective ophthalmic delivery system for the treatment of corneal neovascularization: in vitro and in vivo evaluation

Naringenin, a flavonoid, possesses antiangiogenic potential and inhibits corneal neovascularization (CNV); however, its therapeutic use is restricted due to poor solubility and limited bioavailability. In this study, we developed a naringenin microemulsion (NAR-ME) for inhibiting CNV. NAR-ME formulation was composed of triacetin (oil phase), Cremophor RH40 (CRH40), PEG400, and water, its droplet size was 13.22 ± 0.13 nm with a narrow size distribution (0.112 ± 0.0014). The results demonstrated that NAR-ME released higher and permeated more drug than NAR suspension (NAR-Susp) in in vitro drug release and ex vivo corneal permeation study. Human corneal epithelial cells (HCECs) toxicity study showed no toxicity with NAR-ME, which is consistent with the result of ocular irritation study. NAR-ME had high bioavailability 1.45-fold, 2.15-fold, and 1.35-fold higher than NAR-Susp in the cornea, conjunctiva, and aqueous humor, respectively. Moreover, NAR-ME (0.5% NAR) presented efficacy comparable to that of dexamethasone (0.025%) in the inhibition of CNV in mice CNV model induced by alkali burning, resulting from the attenuation of corneal vascular endothelial growth factor (VEGF) and matrix metalloproteinase (MMP-14) expression. In conclusion, the optimized NAR-ME formulation demonstrated excellent physicochemical properties and good tolerance, enhanced ocular bioavailability and corneal permeability. This formulation is promising, safe, and effective for the treatment of CNV.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Ten Years of Knowledge of Nano-Carrier Based Drug Delivery Systems in Ophthalmology: Current Evidence, Challenges, and Future Prospective

The complex drug delivery barrier in the eye reduces the bioavailability of many drugs, resulting in poor therapeutic effects. It is necessary to investigate new drugs through appropriate delivery routes and vehicles. Nanotechnology has utilized various nano-carriers to develop potential ocular drug delivery techniques that interact with the ocular mucosa, prolong the retention time of drugs in the eye, and increase permeability. Additionally, nano-carriers such as liposomes, nanoparticles, nano-suspensions, nano-micelles, and nano-emulsions have grown in popularity as an effective theranostic application to combat different microbial superbugs. In this review, we summarize the nano-carrier based drug delivery system developments over the last decade, particularly review the biology, methodology, approaches, and clinical applications of nano-carrier based drug delivery system in the field of ocular therapeutics. Furthermore, this review addresses upcoming challenges, and provides an outlook on potential future trends of nano-carrier-based drug delivery approaches in ophthalmology, and hopes to eventually provide successful applications for treating ocular diseases.

Phase Transition Microemulsion of Brimonidine Tartrate for Glaucoma Therapy: Preparation, Characterization and Pharmacodynamic Study

Purpose: The aim of this study was to formulate brimonidine tartrate loaded phase transition microemulsions (PMEs), which undergo phase transition from water in oil (W/O) microemulsions to liquid crystalline (LC) and then oil in water (O/W) microemulsions after instilled into the eye and prolong the precorneal residence time and ocular bioavailability for the effective treatment of glaucoma.Methods: The pseudo-ternary phase diagram was developed and various PMEs were prepared using Tween 80 and Span 80 with isopropyl myristate and water. Globule size and shape, physicochemical parameters, in vitro and ex vivo drug release of PMEs were studied. The in vivo anti-glaucoma efficacy of optimized PMEs was studied in an experimental rabbit eyes model and compared with marketed formulation (MF).Results: Globule size of PMEs was found less than 200 nm, which was confirmed by both dynamic light scattering technique and Transmission Electron Microscopy. Physicochemical properties such as pH, refractive index, percentage transparency, viscosity and conductivity were also found in the acceptable ranges. In vitro release studies of PMEs exhibited sustained release property. Ex vivo permeation study also supported the enhanced drug flux through cornea from PMEs as compared with MF. In pharmacodynamic study, a greater reduction in intraocular pressure was seen in PMEs as compared to MF.Conclusion: PMEs as ocular drug delivery system offer a promising approach to enhance the corneal contact, higher permeation and prolonged precorneal retention time in the eye leading to sustained drug release, enhanced bioavailability and patient compliance.

Ocular microemulsion of brinzolamide: Formulation, physicochemical characterization, and in vitro irritation studies based on EpiOcular™ eye irritation assay

In recent years, the hydrophobic active substances have led researchers to develop new formulations to enhance bioavailability and dissolution rate; brinzolamide, a lipophilic drug belongs to carbonic anhydrase inhibitors, which cause reduction of intraocular pressure in patients suffering from glaucoma. Currently, the marketed product of brinzolamide is in the form of ocular drops; nonetheless, the conventional drops provide decreased therapeutic efficacy owing to their low bioavailability and pulsed drug release. Thus, the development of novel ocular formulations such as topical microemulsions is of high importance. In this work, the preparation of new microemulsions containing brinzolamide (0.2, 0.5 and 1% w/w) and comprised from isopropyl myristate, tween 80 and span 20 and Cremophor EL was performed. The obtained microemulsions were further characterized for their physicochemical properties. In addition, Fourier Transformed-Infrared spectroscopy was used touate the compatibility of active ingredients and components. In vitro release studies along with kinetic modeling were performed using the dialysis membrane method in simulated tear fluid. Bioadhesion studies were performed using Texture analysis. Finally, in vitro ocular irritation based on EpiOcular™ Eye Irritation Test and cytocompatibility studies was performed to examine any possible harm on ocular cells and predict in vivo safety profile.

Lipid-Based Nanocarriers as Topical Drug Delivery Systems for Intraocular Diseases

Effective drug delivery to intraocular tissues remains a great challenge due to complex anatomical and physiological barriers that selectively limit the entry of drugs into the eye. To overcome these challenges, frequent topical application and regular intravitreal injections are currently used to achieve the desired drug concentrations into the eye. However, the repetitive installation or recurrent injections may result in several side effects. Recent advancements in the field of nanoparticle-based drug delivery have demonstrated promising results for topical ophthalmic nanotherapies in the treatment of intraocular diseases. Studies have revealed that nanocarriers enhance the intraocular half-life and bioavailability of several therapies including proteins, peptides and genetic material. Amongst the array of nanoparticles available nowadays, lipid-based nanosystems have shown an increased efficiency and feasibility in topical formulations, making them an important target for constant and thorough research in both preclinical and clinical practice. In this review, we will cover the promising lipid-based nanocarriers used in topical ophthalmic formulations for intraocular drug delivery.

Tailored Limonene-Based Nanosized Microemulsion: Formulation, Physicochemical Characterization and In Vivo Skin Irritation Assessment

Purpose: Microemulsion (ME) achieved progressing consequences on both the research and industry levels due to their distinctive properties. ME based-limonene system is considered as a surrogate to the traditional microemulsion composed of conventional oils. Thus, a novel microemulsion based on D-limonene and Gelucire® 44/12 had been designed and evaluated with assessing the factors affecting its physicochemical characteristics and in vivo skin irritation.

Methods: The impact of microemulsion components and ratios on the isotropic region of the pseudo-ternary phase diagram was investigated. The optimal formula was evaluated in terms of percentage transmittance, average globule size, size distribution, zeta potential, microscopical morphology, stability under different storage conditions and its effect on the mice ear skin.

Results: The results demonstrated that Labrasol® and Labrafil® M 1944 CS had been selected as surfactant and co-surfactant, respectively, due to their emulsifying abilities. The largest isotropic area in the pseudo-ternary phase diagram was at a weight ratio of 4:1 for Labrasol® and Labrafil® M 1944 CS. The optimized microemulsion with 25% w/w of the lipid phase and 58.3% w/w of the aqueous phase displayed an optical transparency of 96.5±0.88 %, average globule size of 125±0.123 nm, polydispersity index of 0.272±0.009, zeta potential of -18.9± 2.79 mV with rounded globules morphology and high stability. The in vivo skin irritation and the histopathological evaluation of microemulsion elucidated its safety profile when applied on the skin.

Conclusion: The formulated microemulsion is a prospective aid for an essential oil to minimize its volatility, enhance its stability, and mask its dermal irritant.

Formulation of chitosan coated nanoliposomes for the oral delivery of colistin sulfate: in vitro characterization, 99mTc-radiolabeling and in vivo biodistribution studies

Colistin sulfate is a very important antibiotic for the treatment of multidrug-resistant Gram-negative infections. Unfortunately, it has low oral bioavailability and several side effects following parenteral administration. The present study aims to develop chitosan-coated colistin nanoliposomes to improve the stability in the gastrointestinal tract and to enhance the oral delivery of colistin. The chitosan-coated colistin nanoliposomes were obtained via thin-film evaporation and electrostatic deposition methods using either Span 60, Tween 65 or Tween 80 as surfactants with different cholesterol: surfactant: soya lecithin ratios. The influence of systems variables was further characterized by vesicle size analysis, zeta potential (ZP), poly dispersibility index (PDI), and also their entrapment efficiency percentage (EE %) was evaluated. Various systems were formed with vesicle sizes in the nano-range, 155.64 ± 12.53 nm to 315.64 ± 15.90 nm, and EE % of 45.2 ± 2.9% to 81.8 ± 2.9%. Moreover, the ZP value of the prepared nanoliposomes switched from a negative to a positive value after chitosan coating. To track the released colistin in vivo, technetium 99m (^99mTc) was incorporated into the optimum system (S-3) system via direct coupling with colistin. Chitosan-coated ^99mTc-colistin nanoliposome, ^99mTc-colistin suspension, and ^99mTc-chitosan-coated nanoliposomes (placebo) were administered orally into bacterial infection (Escherichia coli) bearing mice. The biodistribution results showed that chitosan-coated nanoliposome significantly enhanced the bioavailability of colistin compared to colistin suspension (the commercially available). Moreover, the system effectively improved the localization of colistin at the infected muscle. In conclusion, this approach offers a promising tool for enhanced oral delivery of colistin.

FbD Supported Development and In Vitro Evaluation of Carbomer based Resveratrol Loaded Topical Antipsoriatic Nanoemulgel for its Targeted Skin Delivery

BACKGROUND

Resveratrol is a wonder therapy for the treatment of several skin disorders, including psoriasis, but its skin permeation limits its applications.

OBJECTIVE

The present work dealt with optimizing and formulating resveratrol loaded vitamin E based nanoemulsion and carbomer based nanoemulgel intended for topical application in the treatment of plaque psoriasis. The major objective of this study was to achieve the quality target product profile with respect to enhanced skin permeation and superior skin deposition of the formulated nanoemulgel to achieve the superlative therapeutic advantages.

METHODS

Formulation by design (FbD) approach was employed to optimize varied critical material attributes such as the concentration of oil and Smix to achieve the desired quality characteristics. Carbomer based nanoemulgel was formulated and evaluated.

RESULTS

Optimized formulation was having globule size (168.3 ± 4.98 nm), percentage cumulative permeation (4.81 ± 0.65%), permeation flux (7.62 ± 0.39 μg hr-1cm-2), and skin deposition (668.65 ± 11.98 μg cm-2). Nanoemulgel was found to have optimum physical properties in terms of viscosity, spreadability, pH and physical stability. The extent of skin deposition was approximately 6.682 times higher while the permeation enhancement ratio was around 2.872 as compared to conventional formulation indicating its higher skin targeting abilities, which was further ratified by Confocal Laser Scanning Microscopy results.

CONCLUSION

Nanoemulgel formulated by the current FbD approach has enhanced skin permeation and skin deposition properties as compared to conventional carbomer gel. Thus, it could augment the therapeutic benefits of encapsulated bioactive in the treatment of several skin disorders like psoriasis.

Treatment of Severe Infectious Keratitis With Scleral Contact Lenses as a Reservoir of Moxifloxacin 0.5

PURPOSE

To report the outcomes of using scleral contact lenses as antibiotic reservoirs as a therapeutic approach in a case series of severe infectious keratitis and to discuss the clinical potential.

METHODS

This was a prospective consecutive case series study of 12 eyes treated for infectious keratitis at the "Conde de Valenciana" Institute of Ophthalmology. A scleral lens (SL) filled with 0.5% moxifloxacin was used as a reservoir and replaced every 24 hours until epithelization was complete or the culture report and/or antibiogram demonstrated either a microorganism not susceptible to or resistant to moxifloxacin.

RESULTS

The study included 12 eyes of 12 patients (7 women; 58.33%; average age of 63 ± 20.11 years). All patients completed at least 1 month of follow-up. Patients had a diagnosis of infectious keratitis, and the SL was fitted on initial consultation. Of the 12 eyes, 7 had culture-positive bacterial infection, 2 eyes were mycotic, and 3 eyes had no culture growth. In 3 eyes, SL was discontinued because of the lack of response (one eye) and to the presence of mycotic infection (2 eyes). All infections resolved favorably at the final follow-up.

CONCLUSIONS

The use of SLs could be an alternative for antibiotic impregnation and treatment of infectious keratitis. No complications or side effects were observed related to the use of the scleral contact lens as a reservoir for the antibiotic. This treatment modality could offer a comfortable treatment for the patient, ensuring good impregnation and maintenance of antibiotic concentrations during the 24-hour wear periods.

Nanoemulsion as a feasible and biocompatible carrier for ocular delivery of travoprost: Improved pharmacokinetic/pharmacodynamic properties

Travoprost is a synthetic prostaglandin F2α analogue used in treatment of glaucoma. Due to its water insolubility and oily nature, novel delivery systems need to be developed to enhance its bioavailability, and sustain its release. In the current work, travoprost nanoemulsion was explored as a novel carrier prepared using low energy technique. Results showed that travoprost nanoemulsions exhibited suitable nanodroplet size, zeta potential, pH, refractive index, controlled release, as well as sufficient stability under accelerated conditions. In vivo studies delineated the enhanced absorption of travoprost nanoemulsion compared to the marketed eye drops Travatan®, as proven by the higher C_max and AUC of the former, and its prolonged intraocular pressure reduction time. Moreover, the nanoemulsion formulation was proven safe and non-irritant to ocular surfaces. Therefore, it can be suggested that travoprost nanoemulsion is a promising ocular delivery system for glaucoma treatment.

Novel Ocular Drug Delivery Systems: An Update on Microemulsions

Sufficient ophthalmic drug delivery is still challenging for pharmaceutical technologists, despite various scientific efforts. Several ocular drug carriers have been designed to enhance bioavailability by prolonging the drug retention time. One of the current encouraging approaches is the utilization of colloidal carriers with the characteristic submicron-nanometer size. Microemulsions (MEs) are such colloid systems that present sizes between 5 and 200 nm with significant thermodynamic stability and low surface tension. In addition, MEs as topical ocular carriers can lead to great ocular drug adsorption due to their enhanced retention time. Furthermore, considering that MEs are stable for long time and various temperatures, their ocular application is of great interest. The aim of this study is to cover basic physicochemical principals of ocular MEs such as their possible size, stability, and therapeutic efficacy against various eye disorders. Thus, a comprehensive review for ocular drug delivery systems in the form of MEs that show promising characteristics as their stability and therapeutic efficiency is performed.

Once Daily Pregabalin Eye Drops for Management of Glaucoma

Elevated intraocular pressure (IOP) is the most significant risk factor contributing to visual field loss in glaucoma. Unfortunately, the deficiencies associated with current therapies have resulted in reduced efficacy, several daily dosings, and poor patient compliance. Previously, we identified the calcium voltage-gated channel auxiliary subunit alpha2delta 1 gene (Cacna2d1) as a modulator of IOP and demonstrated that pregabalin, a drug with high affinity and selectivity for CACNA2D1, lowered IOP in a dose-dependent manner. Unfortunately, IOP returned to baseline at 6 h after dosing. In the current study, we develop a once daily topical pregabalin-loaded multiple water-in-oil-in-water microemulsion formulation to improve drug efficacy. We characterize our formulations using multiple in vitro and in vivo evaluations. Our lead formulation provides continuous release of pregabalin for up to 24 h. Because of its miniscule droplet size (<20 nm), our microemulsion has a transparent appearance and should not blur vision. It is also stable at one month of storage at temperatures ranging from 5 to 40 °C. Our formulation is nontoxic, as illustrated by a cell toxicity study and slit-lamp biomicroscopic exams. CACNA2D1 is highly expressed in both the ciliary body and the trabecular meshwork, where it functions to modulate IOP. A single drop of our lead pregabalin formulation reduces IOP by greater than 40%, which does not return to baseline until >30 h post-application. Although there were no significant differences in the amplitude of IOP reduction between the formulations we tested, a significant difference was clearly observed in their duration of action. Our multilayered microemulsion is a promising carrier that sustains the release and prolongs the duration of action of pregabalin, a proposed glaucoma therapeutic.

Novel drug delivery methods for the treatment of keratitis: moving away from surgical intervention

Introduction: Corneal ulceration is one of the leading causes of blindness especially in low- and mid-income countries (LMICs). Surgical treatment of microbial keratitis is associated with multiple challenges that include non-availability of donor corneal tissues, lack of trained corneal surgeons, and poor compliance to follow up care. As a result, the surgery fails in 70-90% cases. Therefore, improving outcome of medical treatment and thereby avoiding the need for the surgery is an unmet need in the care of corneal ulcer cases.Areas covered: In this review article, the authors have tried to compile information on the novel drug-delivery systems that have potential to enhance success of medical management. We have discussed the following systems: cyclodextrins, gel formulations, colloidal system, nanoformulations, drug-eluting contact lens, microneedle patch, and ocular inserts.Expert opinion: The goals of corneal ulcer treatment are as follows: rapid eradication of causative microorganisms, control of damage from induced inflammation and microbial toxins, and facilitation of repair. The ocular surface anatomy poses several challenges for drug delivery using standard topical therapy. The novel drug-delivery systems mentioned above aim to enhanced tear solubility; superior stability; improved bio-availability; reduced toxicity; besides facilitating targeted drug delivery and convenience of administration.

Corneal targeted Sertaconazole nitrate loaded cubosomes: Preparation, statistical optimization, in vitro characterization, ex vivo permeation and in vivo studies

Sertaconazole nitrate (STZ) is a poorly soluble antifungal drug commonly used for treating fungal skin infections. Introducing it as a new treatment option for the management of fungal keratitis, requires the development of a delivery system capable of targeting the infected cornea with an adequate STZ concentration. Hence, Sertaconazole nitrate loaded cubosomes (STZ-CUBs) were prepared, characterized and optimized based on a 3³ central composite face-centred design. Optimized formulation (CUB-opt) showed maximum desirability (0.905), with solubilization efficiency (SE%) of 94.50 ± 0.51%, particle size (PS) of 216.55 ± 2.33 nm, polydispersity index (PDI) of 0.229 ± 0.11 and zeta potential (ZP) of 34.00 ± 6.93 mV. Under the transmission electron microscope, it showed discrete cubic shaped structures. Moreover, it exhibited a promising mucoadhesive behavior, terminal sterilization stability, and storage stability. Ex vivo corneal permeation study revealed its ability to enhance the steady state flux (J_ss) and the permeability coefficient (K_P) of STZ, compared to STZ-suspension. Finally, CUB-opt formulation was found to be safe on the corneal tissues in the in vivo corneal tolerance study, and demonstrated a superior corneal penetration power in the in vivo corneal uptake study.

Potentiality of microemulsion systems in treatment of ophthalmic disorders: Keratoconus and dry eye syndrome - In vivo study

Microemulsions are widely studied as potential ocular drug delivery vehicles. In the present study we show the versatility of possible use microemulsions as ocular delivery vehicle. The ME is loaded with a hydrophilic drug, riboflavin phosphate (RFP) and a lipophilic, docosahexaenoic acid in triglyceride form (TG-DHA), each separately. These drugs treat keratoconus and dry eye syndrome, respectively. The advantage of using ME loaded with RFP is in overcoming eye epithelium debridement during collagen cross-linking therapy for treatment of keratoconus. ME loaded with lipophilic TG-DHA provides convenient dosage in liquid aqueous form of administration of highly lipophilic TG-DHA, which is known as a protective molecule in dry eye syndrome. The capability of RFP-loaded MEs was demonstrated in terms of improvement of biomechanical strength of the rabbit cornea, as a result of successful penetration of RFP through the intact epithelium. TG-DHA-loaded microemulsion applied topically onto an eye with induced dry eye syndrome showed the significant relief of the dry eye condition.

Fourth-Generation Antibiotic Gatifloxacin Encapsulated by Microemulsions: Structural and Probing Dynamics

To overcome the increased disease rate, utilization of the versatile broad spectrum antibiotic drugs in controlled drug-delivery systems has been a challenging and complex consignment. However, with the development of microemulsion (μE)-based formulations, drugs can be effectively encapsulated and transferred to the target source. Herein, two biocompatible oil-in-water (o/w) μE formulations comprising clove oil/Tween 20/ethylene glycol/water (formulation A) and clove oil/Tween 20/1-butanol/water (formulation B) were developed for encapsulating the gatifloxacin (GTF), a fourth-generation antibiotic. The pseudoternary phase diagrams were mapped at a constant surfactant/co-surfactant (1:1) ratio to bound the existence of a monophasic isotropic region for as-formulated μEs. Multiple complementary characterization techniques, namely, conductivity (σ), viscosity (η), and optical microscopy analyses, were used to study the gradual changes that occurred in the microstructure of the as-formulated μEs, indicating the presence of a percolation transformation to a bicontinuous permeate flow. GTF showed good solubility, 3.2 wt % at pH 6.2 and 4.0 wt % at pH 6.8, in optimum μE of formulation A and formulation B, respectively. Each loaded μE formulation showed long-term stability over 8 months of storage. Moreover, no observable aggregation of GTF was found, as revealed by scanning transmission electron microscopy and peak-to-peak correlation of IR analysis, indicating the stability of GTF inside the formulation. The average particle size of each μE, measured by dynamic light scattering, increased upon loading GTF, intending the accretion of drug in the interfacial layers of microdomains. Likewise, fluorescence probing sense an interfacial hydrophobic environment to GTF molecules in any of the examined formulations, which may be of significant interest for understanding the kinetics of drug release.

Natural biocide cocktails: Combinatorial antibiotic effects of prodigiosin and biosurfactants

Bacterial secondary metabolites are naturally produced to prevail amongst competitors in a shared habitat and thus represent a valuable source for antibiotic discovery. The transformation of newly discovered antibiotic compounds into effective drugs often requires additional surfactant components for drug formulation. Nature may also provide blueprints in this respect: A cocktail of two compounds consisting of the antibacterial red pigment prodigiosin and the biosurfactant serrawettin W1 is naturally produced by the bacterium Serratia marcescens, which occurs in highly competitive habitats including soil. We show here a combinatorial antibacterial effect of these compounds, but also of prodigiosin mixed with other (bio)surfactants, against the soil-dwelling bacterium Corynebacterium glutamicum taken as a model target bacterium. Prodigiosin exerted a combinatorial inhibitory effect with all tested surfactants in a disk diffusion assay which was especially pronounced in combination with N-myristoyltyrosine. Minimal inhibitory and bactericidal concentrations (MIC and MBC) of the individual compounds were 2.56 μg/mL prodigiosin and 32 μg/mL N-myristoyltyrosine, and the MIC of prodigiosin was decreased by 3 orders of magnitude to 0.005 μg/mL in the presence of 16 μg/mL N-myristoyltyrosine, indicative of synergistic interaction. Investigation of bacterial survival revealed similar combinatorial effects; moreover, antagonistic effects were observed at higher compound concentrations. Finally, the investigation of microcolony formation under combined application of concentrations just below the MBC revealed heterogeneity of responses with cell death or delayed growth. In summary, this study describes the combinatorial antibacterial effects of microbial biomolecules, which may have ecological relevance by inhibiting cohabiting species, but shall furthermore inspire drug development in the combat of infectious disease.

Ophthalmic Drug Delivery Systems for Antibiotherapy-A Review

The last fifty years, ophthalmic drug delivery research has made much progress, challenging scientists about the advantages and limitations of this drug delivery approach. Topical eye drops are the most commonly used formulation in ocular drug delivery. Despite the good tolerance for patients, this topical administration is only focus on the anterior ocular diseases and had a high precorneal loss of drugs due to the tears production and ocular barriers. Antibiotics are popularly used in solution or in ointment for the ophthalmic route. However, their local bioavailability needs to be improved in order to decrease the frequency of administrations and the side effects and to increase their therapeutic efficiency. For this purpose, sustained release forms for ophthalmic delivery of antibiotics were developed. This review briefly describes the ocular administration with the ocular barriers and the currently topical forms. It focuses on experimental results to bypass the limitations of ocular antibiotic delivery with new ocular technology as colloidal and in situ gelling systems or with the improvement of existing forms as implants and contact lenses. Nanotechnology is presently a promising drug delivery way to provide protection of antibiotics and improve pathway through ocular barriers and deliver drugs to specific target sites.

Research on the comparison of the demethylvancomycin's diffusion-deposition characteristics in the ocular solid tissues of sustained subtenon drug delivery with subconjunctival injection

PURPOSE

To compare the demethylvancomycin's diffusion-deposition characteristics in the ocular solid tissues of sustained subtenon drug delivery with subconjunctival injection.

METHOD

Sixty adult white rabbits were randomly assigned to the subtenon drug delivery group and the subconjunctival injection group. The subtenon drug delivery group was continuously infused demethylvancomycin to the subtenon of rabbits. The subconjunctival injection group was injected demethylvancomycin to the subconjunctival of rabbits. Cornea, iris and sclera were collected for high-performance liquid chromatography analyses to determine drug concentrations at one hour, three hours, six hours, 12 h and 24 h of drug administration. WinNonlin 6.3 was used to calculate the parameters of cumulative area under the curve (AUCcum) of demethylvancomycin.

RESULTS

The peak levels of demethylvancomycin concentration of the subtenon drug delivery group and the subconjunctival injection group were 92.406 ± 21.555 and 51.778 ± 14.001 μg/g in cornea, 28.451 ± 10.229 μg/g and 42.271 ± 27.291 μg/g in iris, 153.166 ± 51.738 μg/g and 57.423 ± 18.480 μg/g in sclera. The differences of concentrations between the two groups in cornea and sclera were statistically significant (F = 487.775, p < 0.001; F = 132.748, p < 0.001). The difference in iris was not statistically significant (F = 4.848, p = 0.064). The maximum of AUCcum of the subtenon drug delivery group and the subconjunctival injection group was 1808.23 h * μg/g and 273.73 h * μg/g in cornea, 489.12 h * μg/g and 216.16 h * μg/g in iris and 2166.34 h * μg/g and 392.57 h * μg/g in sclera at 24 h of drug administration.

CONCLUSION

The sustained subtenon drug delivery had a better drug permeability and accumulation in the intraocular solid tissue compared to subconjunctival injection, which demonstrated it was probably a promising and effective approach for treating posterior segment diseases and endophthalmitis.

Microemulsion utility in pharmaceuticals: Implications for multi-drug delivery

Emulsion technology has been utilized extensively in the pharmaceutical industry. This article presents a comprehensive review of the literature on an important subcategory of emulsions, microemulsions. Microemulsions are optically transparent, thermodynamically stable colloidal systems, 10-100nm diameter, that form spontaneously upon mixing of oil, water and emulsifier. This review is the first to address advantages and disadvantages, as well as considerations and challenges in multi-drug delivery. For the period 1 January 2011-30 April 2016, 431 publications related to microemulsion drug delivery were identified and screened according to microemulsion, drug classification, and surfactant types. Results indicate the use of microemulsions predominantly in lipophilic drug delivery (79.4%) via oil-in-water microemulsions and non-ionic surfactants (90%) for oral or topical administration. Cancer is the disease state most targeted followed by inflammatory diseases, microbial infections and cardiovascular disease. Key generalizations from this analysis include: 1) microemulsion formulation is largely based on trial-and-error despite over 1200 publications related to microemulsion drug delivery since their discovery in 1943; 2) characterization using methods including interfacial tension, droplet size, electrical conductivity, turbidity and viscosity may provide additional information for greater predictability; 3) microemulsion drug delivery publications arise primarily from China (27%) and India (21%) suggesting additional research opportunities elsewhere.

Development of microemulsions for ocular delivery

Microemulsions (MEs) are thermodynamic stable dispersion of oily phase and aqueous phase stabilized by surfactants and co-surfactants, and are a small droplet size of less than 100 nm. MEs are appropriate systems for ocular drug delivery because they improve ocular drug retention, extended duration of action, high ocular absorption, permeation of loaded drugs and effortlessness of preparation and administration. This review is an effort to summarize the recent development in the area of MEs, self-emulsifying drug delivery systems, which are examined in relation to their uses in ocular drug delivery. The noteworthy patent, toxicity and stability issues related to these ME systems are also explored here.

The potential use of novel chitosan-coated deformable liposomes in an ocular drug delivery system

In this study, novel chitosan-coated deformable liposomes (DL-CS) were proposed as an ocular drug delivery system to prolong pre-corneal retention, and improve transcorneal penetration and absorption. Flurbiprofen-loaded deformable liposomes (FP-DL) were prepared by a modified ethanol injection method and then coated with chitosan. Both DL and DL-CS exhibited a homogeneous particle size distribution, high encapsulation efficiency and good stability. After coating with 0.1% CS, the zeta potential was shifted from negative to positive. The apparent permeability coefficient of FP-DL-0.1% CS evaluated using isolated rabbit corneas was 1.29-, 1.95- and 4.59- fold greater than that of uncoated FP-DL, conventional liposomes and FP solution (P<0.01), respectively. The in vivo pre-corneal retention time and elimination dynamics were assessed using gamma scintigraphy technology. The area under the remaining activity-time of FP-DL-0.1% CS was prolonged 2.84- and 1.53-fold compared with that of the FP solution and FP-DL groups, respectively. Moreover, the ocular irritation test in vivo revealed that DL-0.1% CS produced no ocular damage or abnormal clinical signs. These results indicate that DL-CS appears to be a novel ophthalmic drug delivery strategy with the potential to overcome the limitations of conventional eye drops.