Sustained Delivery of Timolol Maleate for Over 90 Days by Subconjunctival Injection

Comprehensive ocular and systemic pharmacokinetics of dexamethasone after subconjunctival and intravenous injections in rabbits

Even though subconjunctival injections are used in clinics, their quantitative pharmacokinetics has not been studied systematically. For this purpose, we evaluated the ocular and plasma pharmacokinetics of subconjunctival dexamethasone in rabbits. Intravenous injection was also given to enable a better understanding of the systemic pharmacokinetics. Dexamethasone concentrations in plasma (after subconjunctival and intravenous injections) and four ocular tissues (iris-ciliary body, aqueous humour, neural retina and vitreous) were analysed using LC-MS/MS. Population pharmacokinetic modelling for plasma data from both injection routes were used, and for first time the constant rate of absorption of dexamethasone from the subconjunctival space into plasma was estimated (ka,plasma = 0.043 min-1, i.e. absorption half-life of 17.3 min). Non-compartmental analysis was used for the ocular data analysis and resulting in ocular drug exposure of iris-ciliary body (AUC0-∞= 41984 min·ng/g) > neural retina (AUC0-∞= 25511 min·ng/g) > vitreous (AUC0-∞= 7319 min·ng/mL) > aqueous humour (AUC0-∞= 6146 min·ng/mL). The absolute bioavailability values after subconjunctival injection, reported for the first time, were 0.74 % in aqueous humour (comparable to topical dexamethasone suspensions), and 0.30 % in vitreous humour (estimated to be higher than in topical administration). These novel and comprehensive pharmacokinetic data provide valuable information on the potential for exploiting this route in ocular drug development for treating both, anterior and posterior segment ocular diseases. Moreover, the new generated dexamethasone-parameters are a step-forward in building predictive pharmacokinetic models to support the design of new subconjunctival dexamethasone formulations, which may sustain drug effect for longer period of time.

Synthesis of novel interpenetrated network for ocular co-administration of timolol maleate and dorzolamide hydrochloride drugs

In the present work, novel interpenetrated networks (IPNs) of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide) (SBMA) and poly(vinyl alcohol) (PVA) were prepared for the ocular co-administration of timolol maleate (TIM) and dorzolamide hydrochloride (DORZ), two drugs widely used for the treatment of glaucoma. The successful polymerization of SBMA, in the presence of PVA, led to the formation of semi-interpenetrated pSBMA-PVA networks (IPNs), in the form of sponges, exhibiting intrinsic antimicrobial properties attributed to SBMA. Fourier-transform infrared spectroscopy (FTIR) was utilized to confirm the successful synthesis of the IPNs. Further assessments, including contact angle and water sorption measurements, highlighted their significant hydrophilicity, a feature that makes them suitable for ocular applications. Differential scanning calorimetry (DSC) measurements indicated that PVA serves as a plasticizer, while an assessment of the water sorption capacity of these materials suggested that although the incorporation of PVA results in slightly less hydrophilic materials, the prepared sponges still remain sufficiently hydrophilic for ocular use. Following their characterization, the optimal pSBMA-PVA IPN was used to encapsulate TIM and DORZ. Irritation tests, performed using the HET-CAM method, confirmed that the drug-loaded sponges were safe and potentially well-tolerated for ophthalmic use. Finally, the co-release study for the two drugs revealed a sustained release pattern in both cases, while drug release from the sponges was primarily controlled by diffusion.

Devices and Treatments to Address Low Adherence in Glaucoma Patients: A Narrative Review

Poor adherence to topical glaucoma medications has been linked to worse visual field outcomes in glaucoma patients. Therefore, identifying and overcoming the adherence barriers are expected to slow down the progression of disease. The most common barriers to adherence, in addition to the lack of knowledge, include forgetfulness, side effects of medications, difficulties with drop instillation and low self-efficacy. Symptoms and signs of ocular surface disease, which importantly reduce patients' quality of life, are decreased by using preservative-free topical medications. Sustained drug delivery systems using different vehicles seem promising for relieving the burden of drop administration. Currently, only the bimatoprost sustained-release intracameral implant is available for clinical use and single administration. In the era of digitalization, smart drug delivery-connected devices may aid adherence and, by sharing data with care providers, improve monitoring and adjusting treatment. Selective laser trabeculoplasty as first-line treatment delays the need for drops, whereas minimally invasive glaucoma procedures with and without devices combined with cataract surgery increase the likelihood of patients with early-to-moderate glaucoma to remain drop free or reduce the number of drops needed to control intraocular pressure. The aim of this narrative review is to present and discuss devices and treatments that may improve adherence by reducing the need for drops and side effects of medications and aiding in glaucoma monitoring. For the future, there is a need for studies focusing on clinically important outcomes, quality of life and the cost of intervention with longer post-interventional follow up.

Extraocular, periocular, and intraocular routes for sustained drug delivery for glaucoma

Although once daily anti-glaucoma drug therapy is a current clinical reality, most therapies require multiple dosing and there is an unmet need to develop convenient, safe, and effective sustained release drug delivery systems for long-term treatment to improve patient adherence and outcomes. One of the first sustained release drug delivery systems was approved for the reduction of intraocular pressure in glaucoma patients. It is a polymeric reservoir-type insert delivery system, Ocusert™, placed under the eyelid and on the ocular surface for zero-order drug release over one week. The insert, marketed in two strengths, released pilocarpine on the eye surface. While many clinicians appreciated this drug product, it was eventually discontinued. No similar sustained release non-invasive drug delivery system has made it to the market to date for treating glaucoma. Drug delivery systems under development include punctal plugs, ring-type systems, contact lenses, implants, microspheres, nanospheres, gels, and other depot systems placed in the extraocular, periocular, or intraocular regions including intracameral, supraciliary, and intravitreal spaces. This article discusses the advantages and disadvantages of the various routes of administration and delivery systems for sustained glaucoma therapy. It also provides the reader with some examples and discussion of drug delivery systems that could potentially be applied for glaucoma treatment. Interestingly, one intracamerally injected implant, Durysta™, was approved recently for sustained intraocular pressure reduction. However, long-term acceptance of such devices has yet to be established. The ultimate success of the delivery system will depend on efficacy relative to eye drop dosing, safety, reimbursement options, and patient acceptance. Cautious development efforts are warranted considering prior failed approaches for sustained glaucoma drug delivery. Neuroprotective approaches for glaucoma therapy including cell, gene, protein, and drug-combination therapies, mostly administered intravitreally, are also rapidly progressing towards assessment in humans.

Reporter Scaffolds for Clinically Relevant Cell Transplantation Studies

There are a number of cell therapies that are either in clinical trials or moving toward clinical trials, particularly for diseases of the retina. One of the challenges with cell therapies is tracking the status of cells over time. Genetic manipulation can facilitate this, but it can limit the clinical application of the cells. There are a host of fluorophores that have been developed to assess the status of cells, but these molecules tend to be cleared rapidly from cells. There are preclinical strategies that use degradable scaffolds, and we hypothesized that these scaffolds could be used to track the state of cells during preclinical studies. In this work, we explored whether fluorophores could be delivered from simple scaffolds fabricated under extremely harsh conditions, be active upon release, and report on the cells growing on the scaffolds over time. We encapsulated CellROX® Green Reagent, and pHrodo™ Red AM in poly(lactic-co-glycolic acid) (PLGA) scaffolds, showed that they could be delivered over weeks and were still active upon release and taken up by cells. These experiments provide the foundation for using scaffolds to deliver molecules to report on cells.

Bimatoprost loaded nanovesicular long-acting sub-conjunctival in-situ gelling implant: In vitro and in vivo evaluation

Primary treatment for glaucoma relies on chronic instillation (daily) of intraocular pressure (IOP) lowering eye drops. Present study tends to develop and assess a novel sustained release bimatoprost loaded nanovesicular (BMT-NV) - thermosensitive in-situ gelling implant (BMT-NV-GEL-IM), for subconjunctival delivery. BMT-NVs developed using novel composition and method of preparation, (IPA/700/DEL/2014) and industrially viable methodology were characterized and evaluated comprehensively for ocular suitability. Their incorporation into an in-situ gelling formula was safe (in vitro and in vivo) and stable upon sterilization. Autoclavability was an important consideration, as a preservative-free, single-use BMT-NV-GEL-IM will avoid side- effects associated with repetitive application of drops containing preservatives like benzalkonium chloride (BAK). An extended in vitro release of BMT (80.23%) was observed for 10 days while the IOP lowering effect extended over 2 months with single subconjunctival injection of BMT-NV-GEL-IM in rats. No clinical signs of irritation, inflammation, or infection were observed in any injected eye, throughout the study, as also confirmed by histology. Furthermore, single administration of BMT-NV-GEL as topical drop lowered the IOP over 5 days. Presence of significant diffuse fluorescence in confocal microscopy of internal eye tissues post-in vivo application, as subconjunctival implant, even after 2 month and eye drops upto1 week provide direct evidence of successful sustained delivery. We thus provide an improved modality for antiglaucoma medication in patients who are challenged to adhere to a regimen of daily eye drops.

Co-Delivery of Timolol and Brimonidine with a Polymer Thin-Film Intraocular Device

PURPOSE

We developed a polycaprolactone (PCL) co-delivery implant that achieves zero-order release of 2 ocular hypotensive agents, timolol maleate and brimonidine tartrate. We also demonstrate intraocular pressure (IOP)-lowering effects of the implant for 3 months in vivo.

METHODS

Two PCL thin-film compartments were attached to form a V-shaped co-delivery device using film thicknesses of ∼40 and 20 μm for timolol and brimonidine compartments, respectively. In vitro release kinetics were measured in pH- and temperature-controlled fluid chambers. Empty or drug-loaded devices were implanted intracamerally in normotensive rabbits for up to 13 weeks with weekly measurements of IOP. For ocular concentrations, rabbits were euthanized at 4, 8, or 13 weeks, aqueous fluid was collected, and ocular tissues were dissected. Drug concentrations were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

In vitro studies show zero-order release kinetics for both timolol (1.75 μg/day) and brimonidine (0.48 μg/day) for up to 60 days. In rabbit eyes, the device achieved an average aqueous fluid concentration of 98.1 ± 68.3 ng/mL for timolol and 5.5 ± 3.6 ng/mL for brimonidine. Over 13 weeks, the drug-loaded co-delivery device resulted in a statistically significant cumulative reduction in IOP compared to untreated eyes (P < 0.05) and empty-device eyes (P < 0.05).

CONCLUSIONS

The co-delivery device demonstrated a zero-order release profile in vitro for 2 hypotensive agents over 60 days. In vivo, the device led to significant cumulative IOP reduction of 3.4 ± 1.6 mmHg over 13 weeks. Acceptable ocular tolerance was seen, and systemic drug levels were unmeasurable.

Exploring gelatin nanoparticles as novel nanocarriers for Timolol Maleate: Augmented in-vivo efficacy and safe histological profile

The use of gelatin has been gaining recognition in ocular delivery for its safety profile and biocompatible properties. Timolol Maleate (TM) is an anti-glaucoma drug possessing poor corneal penetration while causing eye irritation making it an ideal candidate for novel nanoparticulate systems. Timolol Maleate loaded Gelatin Nanoparticles (GNPs) were prepared using the double desolvation method utilizing glutaraldehyde as the crosslinking agent. Optimization of the nanoparticles was achieved through a full-factorial design. An optimum formulation possessing particle size of 205 nm, zetapotential of 12.5 mV and an entrapment efficiency of 74.72% was selected. TEM imaging of the optimized nanoparticles was performed and the stability was tracked over 6 months. The in-vitro release studies showed a burst effect followed by a sustained profile. The selected formulae were tested in-vivo and compared to a Timolol marketed product on albino rabbits and were proven superior regarding intraocular pressure lowering and sustained efficacy. The prepared nanoparticles successfully passed Draize irritancy test and showed normal histology. These data indicate that the prepared GNPs possessed all needed qualities of a successful ocular system; corneal affinity, suitable particle size, high entrapment efficiency, sustained release, good stability, efficient lowering of intraocular pressure, high drug bioavailability and lack of irritancy.