Eye Drop Formulation Research Articles

Ocular and Plasma Pharmacokinetics of Sitagliptin Eye Drops: Preclinical Data

Background/Objectives: Early stages of diabetic retinopathy are currently considered an unmet medical need due to the lack of effective treatments beyond proper monitoring and control of glycemia and blood pressure. Sitagliptin eye drops have emerged as a new therapeutic approach against early stages of the disease, as they can prevent its main hallmarks, including both neurodegeneration and microvascular impairment. Interestingly, all of these effects occur without any glycemic systemic improvement. In the present study, we aimed to investigate the pharmacokinetics and distribution of the drug within the eye and plasma. Methods: A total of 48 male New Zealand rabbits were treated with topical administration (eye drops) of sitagliptin at two concentrations: 5 mg/mL and 10 mg/mL. Blood, iris/ciliary body, retina/choroid, aqueous humor, and vitreous humor samples were collected at specific intervals post-administration (10 and 30 min and 1, 3, 6, 15, and 24 h), processed, and analyzed using an LC-MS/MS method. The pharmacokinetics of sitagliptin were then calculated, and statistical comparisons were performed. Results: Our findings indicate that sitagliptin reaches the retina prior to the aqueous and vitreous humors, suggesting that its absorption follows the transscleral route. Additionally, systemic absorption was minimal and below pharmacologically active concentrations. Conclusions: These results support the use of an eye drop formulation for the treatment of diabetic retinopathy and other retinal diseases.

Sensitive HPLC Method to Support Pre-formulation Studies and to Determine Critical Quality Attributes of Therapeutic Contact Lenses Containing Dorzolamide Hydrochloride

Background: Dorzolamide hydrochloride (DRZ) is a carbonic anhydrase inhibitor used to treat glaucoma and ocular hypertension. Drug-eluting contact lenses, such as Acuvue Theravision ™ with Ketotifen, offer improved drug delivery and reduced side effects compared to eye drops. Drug-loaded nanoparticle-loaded contact lenses can sustain drug release and enhance comfort for extended wear. Objective: High buffer concentration and low pH increase the risk of damage to silica-bonded columns. Therapeutic contact lenses face challenges related to critical lens parameters, including the estimation of drug incorporation and release due to interference of lens matrix leaching. There is currently no analytical method available for estimating DRZ in contact lenses. Method: The HPLC method, which was developed and validated using ICH Q2 (R1) criteria, used a C18 column (250 mm × 4.6 mm, 5 μm) as a stationary phase and methanol:water (70:30 v/v) as the mobile phase. The detecting wavelength was 253 nm. Moreover, to support the efficiency of the developed method, the marketed formulation of DRZ eye drops, drug purity, and loading in contact lenses were analysed. The method was also employed to determine the Critical Quality Attributes (CQAs) of therapeutic contact lenses and drug release and drug leaching during the sterilization process. Result: The developed HPLC method shows Rt for DRZ at 2.881 minutes with good linearity (r2 > 0.998) between 2-32μg/mL, precision (RSD < 2%), accuracy (Recovery > 99.5%), sensitivity, and specificity for quantifying DRZ in marketed formulations and therapeutic contact lenses. The developed method is devoid of any buffer or modifier in the mobile phase, making it safer for the stationary phase. This method mitigates the interference of lens matrix leaching, which induces an overestimation of DRZ. All the result for therapeutic contact lenses was found to be closely aligned with theoretically expected results, confirming the reliability of the developed HPLC method for therapeutic contact lenses. Conclusion: This method is specific, accurate, and precise for quantifying DRZ in commercial formulations and newly developed therapeutic contact lenses. It effectively evaluates the critical quality attributes of these lenses, demonstrating their reliability for assessing their performance and ensuring quality in therapeutic applications.

Citicoline eluting hydrogels for therapeutic contact lenses intended to treat neurodegenerative diabetic ocular diseases

Ophthalmic neurodegenerative diseases related to diabetes, such as glaucoma and retinopathy, are among the major causes of blindness in the world. Citicoline (CIT) in the form of eye drops is currently used for the treatment/prevention of these diseases, which affect the posterior segment of the eye. To ensure the drug penetration into the back of the eye, frequent instillations of highly concentrated drug solutions are required with potential side effects. Drug-loaded soft contact lenses (SCLs) may be an effective alternative to the conventional eye drop treatment, since they may enable a sustained drug release during daily wear, ensuring a higher drug bioavailability, and avoiding drug waste. In this work, one 2-hydroxyethyl methacrylate (HEMA) based hydrogel was functionalised with N-(3-aminopropyl) methacrylamide hydrochloride (APMA), molecularly imprinted with CIT and loaded with the same drug. The material was extensively characterised, in terms of morphology, optical, mechanical, and physical–chemical properties, namely, equilibrium water content, wettability, oxygen and ionic permeability, Young’s modulus, shear deformation, transmittance and refractive index, before and after steam sterilisation. Additionally, the tendency of the material to adsorb proteins of the lachrymal fluid was evaluated and its biocompatibility was assessed by irritation and cytotoxicity assays. Comparison with the non-functionalised and non-imprinted hydrogel showed that the modified hydrogel led to a sustained in vitro release of a much higher amount of CIT than the original one, while keeping typical values for physical–chemical properties of SCLs. The drug-loaded material resisted steam sterilisation and proved to be biocompatible, demonstrating adequate properties to be used in therapeutic SCLs for the prophylaxis/treatment of neurodegenerative diabetic ocular diseases. The neuroprotective effect of the released drug was confirmed with tests using porcine retinal explants.

Effect of Citric Acid and Tromethamine on the Stability of Eyedrops Containing Lifitegrast.

Lifitegrast is an effective treatment for dry eye disease, reducing inflammation and improving the ocular surface condition. Owing to its high sensitivity to oxidation and hydrolysis, formulation studies are required to maintain the physicochemical stability of lifitegrast. This study aimed to overcome the instability of lifitegrast by developing a more stable eyedrop formulation by using citric acid and tromethamine to prevent the degradation of lifitegrast. Based on the Design of Experiment (DoE) approach, formulations were prepared at various concentrations of two stabilizers, citric acid and tromethamine. The stabilizers were carefully controlled to reduce the generation of degradation products. The eyedrops were stored under accelerated test conditions, and parameters such as appearance, pH, drug content, and impurities were evaluated. The results showed that all critical quality attributes (CQAs) including appearance, pH, drug content, and impurities were maintained at stable levels under accelerated conditions, meeting established criteria. In addition, it was suggested that citric acid provided protection against oxidative stress, while tromethamine prevented hydrolysis caused by pH fluctuations. Consequently, it was concluded that the developed lifitegrast-containing eyedrop formulation exhibited improved physicochemical stability, validated through statistical analyses. These findings contribute to the development of stable eyedrops and provide a foundation for commercial production and clinical applications.

A Preservative-Free Combination of Sodium Hyaluronate and Trehalose Improves Dry Eye Signs and Symptoms and Increases Patient Satisfaction in Real-Life Settings: The TEARS Study.

Dry eye disease (DED) is a frequently observed condition characterized by ocular discomfort and visual disturbance. It is highly prevalent and impairs patients' quality of life (QoL). This study assessed the benefit of a preservative-free bioprotectant eye drop formulation containing sodium hyaluronate and trehalose (SH-trehalose) with regards to DED, as well as patient satisfaction, through a large-scale real-life survey. In a multi-center, international, prospective observational study, subjects with DED received SH-trehalose for 84 days. Ocular Surface Disease Index (OSDI), Dry Eye Questionnaire-5 items (DEQ-5), and patient satisfaction were assessed at baseline, day 28, and day 84, and clinical evaluations included ocular surface staining, Schirmer test, tear film break-up time (TBUT), and conjunctival hyperemia at baseline and day 84. A total of 312 patients were evaluated, of whom 82.4% were women. The mean age was 57.9±15.2 years. The mean OSDI score at baseline was 41.7 ± 20.6. After 84 days, the mean OSDI score was 27.3 ± 19.8 (p < 0.001). The percentage of patients with a severe OSDI score decreased from 60.3 to 34.5%. The DEQ-5 score significantly (p < 0.001) improved after 28 and 84 days, as did patient satisfaction. Ocular surface staining, Schirmer test, TBUT, and conjunctival hyperemia scores improved significantly (all p < 0.001) for both eyes with SH-trehalose between baseline and day 84. Tolerance of SH-trehalose was good. SH-trehalose significantly improved the clinical signs and symptoms of DED after 84 days. Moreover, it significantly increased patient satisfaction and was well tolerated. NCT04803240.

Hydrogel-Embedded Polydimethylsiloxane Contact Lens for Ocular Drug Delivery.

Topical administration is the commonly preferred method of administering ophthalmic formulations, with the majority of available medications in the form of eye drops or ointments. However, the topical application of ophthalmological medications has less bioavailability and a short residence time because of the physiological and anatomical constraints of the eye, making efficient ophthalmic drug delivery a challenging task. Microfluidic contact lenses have the advantage of delivering drugs into the eye in a controlled and on-demand manner. Here, we showcase the use of hydrogel-embedded microcavities on PDMS-based contact lenses for ocular drug delivery applications. The fabrication technique adopted here is the spontaneous formation of the spherical cavity by hydrogel monomer droplet, followed by the simultaneous thermal curing of hydrogel and PDMS, creating a spherical cavity as small as 150 μm. The spherical cavity is embedded with pH-responsive hydrogel for on-demand drug delivery. The drug loaded in the hydrogel matrix is released into the ocular environment by diffusion. The spherical cavity with a narrow opening restricts the diffusion to a minimum under normal ocular pH conditions(pH > 6). When the ocular pH reduces (pH < 6), the pH-responsive hydrogel inside the spherical cavity deswell and accelerates the drug release.

Dry Eye Para-Inflammation Management: Preclinical and Clinical Evidence on a Novel 0.2% Hyaluronic Acid-Based Tear Substitute with 0.001% Hydrocortisone Sodium Phosphate.

Purpose: An innovative eyedrop formulation based on a combination of 0.2% hyaluronic acid and 0.001% hydrocortisone sodium phosphate (Idroflog®, Alfa Intes, Italy; HAC eyedrops) was granted a European Patent in 2016 and has been available on the market since 2019 in Europe and in other countries around the world. HAC eyedrops aim to synergize the moisturizing effects of hyaluronic acid with the mild anti-inflammatory properties of low-dose hydrocortisone, offering a more effective and safer alternative for treating dry eye disease (DED), targeting both tear film instability and dysfunctional para-inflammation. The activity of HAC eyedrops has been explored in different post-marketing clinical trials, in addition to preclinical studies. In this narrative review, we explored the available evidence on the use of HAC eyedrops for the management of para-inflammation in DED patients to provide a comprehensive overview of efficacy and safety data related to the use of this medical device in routine clinical practice. Methods: A literature search for preclinical and clinical data involving treatment with HAC eyedrops was conducted using PubMed/MEDLINE, considering only original research articles published in English, without time restrictions. Results: One preclinical and four clinical papers were retrieved. Preclinical evidence suggests that 0.001% hydrocortisone is able to control the expression of inflammatory markers, and this, together with the hydrating and lubricating properties of hyaluronic acid, leads to improvements in DED clinical signs, such as tear volume and the stability of the tear film. The results of clinical trials demonstrate that HAC eyedrops are able to improve the signs and symptoms of DED and that 0.001% low-dosage hydrocortisone can be helpful in preventing the progression to chronic stages of DED. Conclusions: HAC eyedrops represent a promising therapeutic strategy for the management of dysfunctional para-inflammation and offer a valuable addition to the armamentarium of treatments for DED.

Clinical Effectiveness, Safety, and Compliance of Two Compounded Formulations of Tacrolimus Eye Drops: An Open-Label, Sequential Prospective Study.

Ophthalmic tacrolimus compounded formulations are usually made from the commercial intravenous presentation, which contains ethanol as a solubilizer due to the low solubility of tacrolimus. The use of cyclodextrins is presented as an alternative to ethanol, an ocular irritant excipient, to avoid its long-term irritant effects. Open-label, sequential, prospective study to compare effectiveness, safety, and adherence of a new formulation of 0.015% tacrolimus with cyclodextrins (TCD) versus 0.03% tacrolimus with ethanol (TE). The ocular evaluation was assessed by ocular signs, corneal staining, subjective questionnaires as Visual Function Questionnaire (VFQ-25) and Visual Analogue Scale (VAS) of symptoms, lacrimal stability, ocular redness, and intraocular pressure. Compliance was assessed by VAS of adherence and empirically (difference between theoretical and actual consumption). Clinical ocular signs and corneal staining score remained stable for most patients 3 months after switching formulations. The TCD formulation did not modify the tear stability and intraocular pressure of the treated patients compared to the TE formulation. TCD eye drops significantly decreased the subjective pain values on VFQ-25 scale and burning sensation on the VAS symptom scale in comparison to TE formulation after 3 months after the change to TCD formulation. The novel tacrolimus in cyclodextrins formulation is a promising alternative for treating inflammatory ocular pathologies refractory to first-line treatments.

Ex Vivo Irritation Evaluation of a Novel Brimonidine Nanoemulsion Using the Hen's Egg Test on Chorioallantoic Membrane (HET-CAM).

The hen's egg test on chorioallantoic membrane (HET-CAM) assay is a cost-effective and well-validated, non-animal-based ex vivo method for evaluating the irritant potential and eye toxicity of substances. A colloidal dispersion of a surfactant and a cosurfactant with a nanosize range is called a nanoemulsion (NE), which is formed by mixing immiscible liquids and stabilized by surfactants. Patients with glaucoma are commonly prescribed Brimonidine (BR), an alpha-2 adrenergic agonist, to lower their intraocular pressure. In this study, surfactant-cosurfactant blends were prepared by mixing Tween 80 (surfactant) and propylene glycol (cosurfactant) in a 4:1(v/v) ratio. Triacetin served as the oil phase, while deionized water was used as the aqueous phase. Using the drop method, a range of NE formulations (F1, F2, F3, FB1, FB2, and FB3) were developed and subsequently evaluated for their potential to irritate, and then the results were compared to those of a commercially available BR eye drop formulation. According to the average cumulative HET-CAM test scores (IS), from excipients, propylene glycol caused moderate irritation by causing slight damage to blood vessels. The formulations FB1 and F1 were found to have the highest level of irritation among other formulations in the investigation, recording 1.05 ±0.07 and 1.2 ±0.10, respectively. All other NE formulations exhibited non-irritating potential, as confirmed by the HET-CAM test, and were comparable to the marketed BR eye drop formulation. The NE formulations created for BR were determined to be safe and non-irritating. The findings indicate that the prepared NE could be a beneficial solution for addressing problems with conventional eye drops and delivering BR effectively to the eyes.

Treatment of endophthalmitis using a novel methacrylic anhydride-modified hydroxypropyl methylcellulose hydrogels loaded with S-nitrosoglutathione: An ex-vivo keratitis model

Introductionpost-operative endophthalmitis (POE) following cataract surgery remains a significant concern due to its impact on vision and the associated socio-economic burden. S-Nitrosoglutathione (GSNO) shows promise due to its stability and antimicrobial properties. Hydroxypropyl methylcellulose (HPMC) is commonly used in eye drops for drug retention, while methacrylic anhydride (MA) modification enhances adhesion. In our study, we aimed to develop a novel GSNO-loaded HPMC-MA hydrogel, and used an ex-vivo corneal keratitis model to test the anti-inflammatory and anti-microbial effects of HPMC-MA hydrogels containing GSNO. Additionally, the study evaluated the irritative potential of the eye drop formulation containing GSNO-loaded HPMC-MA hydrogels on rabbit eyes. MethodWe prepared and tested the GSNO-loaded HPMC-MA hydrogels characters. Fourier Transform Infrared (FTIR) spectroscopy measurement to verify modification, cell viability assays, osmolality tests, in-vivo ocular irritation assessments, inflammatory cells genes expression using RT-PCR, bacterial concentration analysis with an ex-vivo S. aureus keratitis model were conducted. ResultsFTIR spectroscopy confirmed successful MA modification and GSNO incorporation. Cell viability experiments suggested optimal GSNO concentration at 80 μM. Osmolality tests indicated no significant changes in osmolality post-modification. Ocular irritation tests on rabbits showed no adverse reactions. In the ex-vivo keratitis model, GSNO-HPMC-MA reduced inflammation and inhibited bacterial growth, as reflected in gene expression and bacterial concentration analyses. ConclusionThe study demonstrates the successful development of GSNO-loaded HPMC-MA hydrogels with potential as a topical formulation for endophthalmitis treatment. This novel approach shows promise in addressing challenges related to drug delivery efficiency and antimicrobial efficacy in ocular infections.

Imaging-Based Drug Penetration Profiling in an Excised Sheep Cornea Model.

Formulations designed to address ocular conditions and diseases are predominantly administered topically. While in vitro test systems have been developed to assess corneal permeation under extended contact conditions, methods focusing on determining the penetration depth and kinetics of a substance within the cornea itself rather than through it, are scarce. This study introduces a method for time-dependent penetration depth analysis (10 and 60 min) by means of a semiquantitative imaging method in comparison with a quantitative corneal depth-cut technique, employing fluorescein sodium at concentrations of 0.2 and 0.4 mg/mL as a small molecule model substance and sheep cornea as a human surrogate. Excised tissues exhibited sustained viability in modified artificial aqueous humor and maintained thickness (746 ± 43 µm) and integrity (electrical resistance 488 ± 218 Ω∙cm2) under the experimental conditions. Both methods effectively demonstrated the expected concentration- and time-dependent depth of penetration of fluorescein sodium, displaying a significantly strong correlation. The traceability of the kinetic processes was validated with polysorbate 80, which acted as a penetration enhancer. Furthermore, the imaging-based method enabled detecting the retention of larger structures, such as hyaluronic acid and nanoemulsions from the commercial eyedrop formulation NEOVIS® TOTAL multi, inside the lacrimal layer.

Oxidized cellulose microneedle patch combined with vascular embolization and local delivery of timolol maleate for hemangiomas

Hemangiomas are superficial tumors characterized by dense vascular structures that often affect the patient's aesthetic appearance due to the obvious red appearance on the skin. Current treatments, especially timolol maleate in the form of eye drops and hydrogels, suffer from low transdermal drug delivery rates, resulting in prolonged treatment time. To address this challenge, our study introduced a soluble microneedle patch with dextran as the main material to form microcatheters for sustained delivery of timolol maleate. In addition, we proposed a vascular embolization strategy to disrupt the blood supply in hemangiomas. Oxidized cellulose (C-cellulose) was selected for its excellent hemostatic properties. We incorporated C-cellulose into dextran microneedles to facilitate thrombosis in the vascular-rich areas of hemangiomas. The innovative microneedle patch we developed can penetrate the skin to a depth of 430 μm and dissolve rapidly within 3 minutes, ensuring direct drug delivery to the subcutaneous layer. Notably, the treated skin area regained its original appearance within two hours after treatment. In addition to excellent skin permeability and rapid dissolution, these patches significantly promoted apoptosis and inhibited cell migration in mouse hemangioendothelioma EOMA cells. Our results demonstrate that this approach not only achieves significant tumor inhibition in a mouse hemangioma model, but also represents a more effective, convenient, and non-invasive treatment option. Therefore, dextran/C-cellulose/timolol maleate microneedle patch (MNs/Timolol) has broad clinical application prospects in the treatment of hemangiomas, minimizing the risk of additional damage and improving treatment efficacy.

Quality Control Testing of Chloramphenicol Eye Drops

Background and aims. Choramphenicol is one of important therapeutic options for bacterial conjunctivitis. Its eye drop formulation must possess standards of good quality and sterility. The drug is very sensitive to light and temperature and must be stored between 2 and 8 ᵒ C. This study included testing two of the marketed eye-drops formulations of chloramphenicol of two different origins to ensure quality and efficacy of the drugs. Methods. The test methodology followed same pharmacopeial tests to evaluate both physical and chemical aspects of the drugs tested. Identification tests and assay were carried out. Results. Both products passed the identification tests however, there were different findings and the product from Pakistani company failed to comply with BP limits for the pH range and assay. Conclusion. It is of great importance to check on some drugs to see if affected during transport and distribution by testing samples collected randomly from pharmacies.

MEIBO (perfluorohexyloctane): a novel approach to treating dry eye disease.

Dry eye disease (DED) or keratoconjunctivitis sicca (KCS) is a multifactorial disease that classically develops due to the hyperosmolarity of the tear film. Categorically divided into two types, based on decreased production and increased evaporation of the tear film, DED begins with a spectrum of nonspecific symptoms like pruritus, redness, burning and discomfort, progressively leading to stringy mucus eye discharge, photophobia, twitching, visual fluctuations, and punctate epithelial lesions. This disease has numerous treatment options, including medications, artificial tear inducers, and surgical manoeuvres that prevent water loss from the tear film. However, each of these treatment options has its limitations. The Food and Drug Administration (FDA) has approved another intervention, Meibo (perfluorohexyloctane), as a choice of management for dry eye disease. With its shielding action on the ocular surface, Meibo (perfluorohexyloctane) reduces desiccation stress-induced ocular damage, making it highly specific for treating DED. Available in an eye drop formulation of perfluorohexyloctane (PFHO), these drops can reduce saline evaporation by up to 80%. The methods we used for this analysis are literature searches from PubMed, Medline and Google Scholar. This study aims to scour varying differentials of DED, its aetiology, general interventions, the latest refinements, and clinical efficacy, safety, and trials associated with Meibo (perfluorohexyloctane) in the management of DED.

Bilastine 0.6% Preservative-free Eye Drops: A Once-daily Treatment for Allergic Conjunctivitis.

Bilastine is a second-generation antihistamine approved for the symptomatic treatment of allergic rhinoconjunctivitis and urticaria. The present trial evaluated the efficacy and safety of a new bilastine 0.6% preservative-free eye drop formulation for the symptomatic treatment of allergic conjunctivitis. This phase 3, multicenter, double-masked, randomized study compared the efficacy, safety, and tolerability profile of bilastine 0.6% ophthalmic solution with that of ketotifen 0.025% and vehicle. The primary efficacy endpoint was reduction in ocular itching. The Ora-CAC® Allergen Challenge Model was used to assess ocular and nasal symptoms at 15 minutes (onset of action) and 16 hours after treatment. Patients (N=228) were 59.6% male, and the mean (SD) age was 44.1 (13.4) years. Bilastine demonstrated efficacy in reducing ocular itching compared to vehicle at both onset of action and 16 hours after treatment (P<.001). Symptoms improved with ketotifen compared to vehicle 15 minutes after treatment (P<.001). Bilastine demonstrated statistical noninferiority to ketotifen for all 3 post-CAC timepoints at 15 minutes after instillation, based on an inferiority margin of 0.4. Compared with vehicle, bilastine improved in conjunctival redness, ciliary redness, episcleral redness, chemosis, eyelid swelling, tearing, rhinorrhea, ear and palate pruritus, and nasal congestion at 15 minutes after treatment (P<.05). Ophthalmic bilastine was safe and well tolerated. Mean drop comfort scores were significantly better for bilastine than for ketotifen immediately upon instillation (P<.05) and similar to those of vehicle. Ophthalmic bilastine effectively reduced ocular itching for 16 hours after administration, suggesting that it could be used as a once-daily treatment for the signs and symptoms of allergic conjunctivitis. ClinicalTrials.gov identifier: NCT03479307.

Preparation and Physicochemical Evaluation of Eye Drop Formulation Based on Hyaluronic Acid and Vitamin B12

Background Dry eye disease is a common age-related disease in the world. Vitamin B12 is an essential factor in maintaining eye health and has antioxidant properties that protect the surface of the eye from damage caused by harmful factors, such as reactive oxygen species. Hyaluronic acid polymer is also similar to natural eye tears with its biocompatibility and physical properties. This polymer is one of the important components of the extracellular matrix. Objective Due to the lack of formulations containing the combination of vitamin B12 and hyaluronic acid in the country and the appropriate effects of these two compounds for dry eyes, this study formulates and analyzes the stability of eye drop formulation based on hyaluronic acid and vitamin B12. Methods First, the formulation of hyaluronic acid and vitamin B12 solution with borate buffer was prepared and the stability of vitamin B12 was evaluated. Next, the physicochemical properties of the prepared formulations were evaluated and a sterile ophthalmic solution was prepared from the selected formulations under aseptic conditions. Finally, by choosing the final formulation, accelerated stability was achieved. Results Accelerated studies after six months showed that the amount of vitamin B12 and its ultraviolet absorption did not decrease, and the physicochemical properties, such as solution pH, color, and viscosity did not change. Conclusion This formulation could be a good candidate for industrial production and long-term stability studies are recommended.

Molecular Mechanisms and Therapeutic Potential of Gabapentin with a Focus on Topical Formulations to Treat Ocular Surface Diseases.

Gabapentin (GBP) was originally developed as a potential agonist for Gamma-Amino-Butyric-Acid (GABA) receptors, aiming to inhibit the activation of pain-signaling neurons. Contrary to initial expectations, it does not bind to GABA receptors. Instead, it exhibits several distinct pharmacological activities, including: (1) binding to the alpha-2-delta protein subunit of voltage-gated calcium channels in the central nervous system, thereby blocking the excitatory influx of calcium; (2) reducing the expression and phosphorylation of CaMKII via modulation of ERK1/2 phosphorylation; (3) inhibiting glutamate release and interfering with the activation of NMDA receptors; (4) enhancing GABA synthesis; (5) increasing cell-surface expression of δGABA_A receptors, contributing to its antinociceptive, anticonvulsant, and anxiolytic-like effects. Additionally, GBP displays (6) inhibition of NF-kB activation and subsequent production of inflammatory cytokines, and (7) stimulation of the purinergic adenosine A1 receptor, which supports its anti-inflammatory and wound-healing properties. Initially approved for treating seizures and postherpetic neuralgia, GBP is now broadly used for various conditions, including psychiatric disorders, acute and chronic neuropathic pain, and sleep disturbances. Recently, as an eye drop formulation, it has also been explored as a therapeutic option for ocular surface discomfort in conditions such as dry eye, neurotrophic keratitis, corneal ulcers, and neuropathic ocular pain. This review aims to summarize the evidence supporting the molecular effects of GBP, with a special emphasis on its applications in ocular surface diseases.

Surface Chemistry Study of Normal and Diseased Human Meibum Films Prior to and after Supplementation with Tear Mimetic Eyedrop Formulation

Ophthalmic nanoemulsions that can treat the deficiencies of meibum (MGS) in Meibomian gland disease and restore its functionality in the tear film are greatly sought. The Rohto Dry Aid (RDA) formulation employs TEARSHIELD TECHNOLOGYTM, which uses a multicomponent oil phase of polar and non-polar lipid-like molecules selected to mimic the profiles of healthy meibum. Thus, the interactions of RDA with “diseased” Meibomian (dMGS) films merit deeper analysis, as these interactions might offer important clues for both the development of new ocular formulations and the processes behind the therapeutic action of the nanoemulsions. Pseudobinary dMGS/RDA films were spread at the air–water surface of the Langmuir trough. Surface pressure-area isocycles and stress relaxations were used to access the layer’s response to blink-like cycling and dilatational viscoelasticity, respectively, while film morphology was recorded via Brewster angle microscopy. It was found that RDA is able to reverse the brittleness and to restore the stability of “diseased” MGS films and thus to revert the layer’s properties to the functionality of healthy Meibomian lipids. Therefore, in order to effectively treat dry eyes with MGS-oriented therapy, ophthalmic nanoemulsions warrant more research.

Therapeutic Aqueous Humor Concentrations of Latanoprost Attained in Rats by Administration in a Very-High-Molecular-Weight Hyaluronic Acid Eye Drop.

The temporal change in concentration of a novel medicine, Latanoprost (LP), was evaluated in the aqueous humor of rats (6-8-week-old Jcl:Wister rats) when delivered in a very-high-molecular-weight hyaluronic acid (vHiHA) eye drop. Animals were randomly assigned to three treatment groups (LP + vHiHA (LPvHiHA), commercial LP (cLP), and diluted LP (dLP)) and after instilling the eye drops, the aqueous humor (AH) was collected at 0.5, 1, 2, 4, and 6 h to measure the LP concentration using an enzyme-linked immunosorbent assay (ELISA). Although the LP concentration in the LPvHiHA eye drop formulation was 3.57 times lower than in the commercial eye drops used (cLP), the LP concentration in the AH following LPvHiHA administration reached a value close to that of cLP. The cLP was diluted to the same concentration of LP as in the LPvHiHA eye drops for the dLP group, but the LP concentration in the AH of these animals was lower than that of the LPvHiHA rats at all time points. The higher LP concentration in the AH of the LPvHiHA rats suggests that vHiHA may aid the transport of LP across the ocular surface epithelium.

Mucoadhesive, antioxidant, and lubricant catechol-functionalized poly(phosphobetaine) as biomaterial nanotherapeutics for treating ocular dryness.

Dry eye disease (DED) is associated with ocular hyperosmolarity and inflammation. The marketed topical eye drops for DED treatment often lack bioavailability and precorneal residence time. In this study, we investigated catechol-functionalized polyzwitterion p(MPC-co-DMA), composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and dopamine methacrylamide (DMA) monomers, as potential topical nanotherapeutics for DED. The copolymers were synthesized via random free-radical copolymerization, producing different proportions of catecholic functionalization. All as-prepared polymer compositions displayed good ocular biocompatibility. At a feeding ratio of 1:1, p(MPC1-co-DMA1) can facilitate a robust mucoadhesion via Michael addition and/or Schiff base reaction, thus prolonging ocular residence time after 4 days of topical instillation. The hydration lubrication of MPC and radical-scavenging DMA endow the nano-agent to ease tear-film hyperosmolarity and corneal inflammation. A single dose of p(MPC1-co-DMA1) (1mg/mL) after 4 days post-instillation can protect the cornea against reactive oxygen species, inhibiting cell apoptosis and the over-expression of pro-inflammatory factors (IL-6 and TNF-α). In clinical assessment, DED-induced rabbit eyes receiving p(MPC1-co-DMA1) could increase lacrimal fluid secretion by 5-fold higher than cyclosporine A. The catechol-functionalized polyzwitterion with enhanced lubricity, mucoadhesion, and anti-oxidation/anti-inflammation properties has shown high promise as a bioactive eye drop formulation for treating DED.