A study of the dexamethasone sodium phosphate release properties from a periocular capsular drug delivery system

Implantable sustained-release drug delivery systems: a revolution for ocular therapeutics

PURPOSE

Due to the inimitable anatomical structure of the eyeball and various physiological barriers, conventional ocular local administration is often complicated by apparent shortcomings, such as limited bioavailability and short drug retention. Thus, developing methods for sustainable, safe and efficient drug delivery to ocular target sites has long been an urgent need. This study briefly summarizes the barriers to ocular drug administration and various ocular drug delivery routes and highlights recent progress in ocular implantable sustained-release drug delivery systems (DDSs) to provide literature evidence for developing novel ocular implants for sustained drug delivery.

METHODS

We conducted a comprehensive search of studies on ocular implantable sustained-release DDSs in PubMed and Web of Science using the following keywords: ocular, implantable and drug delivery system. More than 400 papers were extracted. Publications focused on sustained and controlled drug release were primarily considered. Experimental articles involving DDSs that cannot be implanted into the eye through surgeries and cannot be inserted into ocular tissues in solid form were excluded. Approximately 143 publications were reviewed to summarize the most current information on the subject.

RESULTS

In recent years, numerous ocular sustained-release DDSs using lipids, nanoparticles and hydrogels as carriers have emerged. With unique properties and systematic design, ocular implantable sustained-release DDSs are able to continuously maintain drug release, effectively sustain the therapeutic concentration in target tissues, and substantially enhance the therapeutic efficacy. Nevertheless, few ocular implantable sustained-release DDSs have been available in clinical use.

CONCLUSIONS

Ocular implantable sustained-release DDSs have become a new focus in the field of ocular drug development through unique designs and improvements in the materials of drug carriers, administration methods and dosage forms. With more ocular implantable sustained-release DDSs being commercialized, ocular therapeutics may be revolutionized.

Controllable continuous sub-tenon drug delivery of dexamethasone disodium phosphate to ocular posterior segment in rabbit

Corticosteroids have been used for treatment of posterior segment eye diseases, but the delivery of drug to the posterior segments is still a problem to resolve. In our study, we explore the feasibility of Sub-tenon's Controllable Continuous Drug Delivery to ocular posterior segment. Controllable continuous sub-tenon drug delivery (CCSDD) system, intravenous injections (IV) and sub-conjunctival injections (SC) were used to deliver dexamethasone disodium phosphate (DEXP) in rabbits, the dexamethasone concentration was measured in the ocular posterior segment tissue by Shimadzu LC-MS 2010 system at different time points in 24 h after first dose injection. Levels of dexamethasone were significantly higher at 12, 24 h in CCSDD than two other approaches, and at 3, 6 h in CCSDD than IV in vitreous body (p < 0.01); at 6, 12, 24 h in CCSDD than two other approaches, and at 1, 3 h in CCSDD than IV in retinal/choroidal compound (p < 0.01); at 3, 6, 12, 24 h in CCSDD than two other approaches, and at 1 h in CCSDD than IV in sclera (p < 0.05). The AUC0-24 in CCSDD group is higher than two other groups in all ocular posterior segment tissue. Our results demonstrated that dexamethasone concentration could be sustained moderately higher in the posterior segment by CCSDD than SC and IV, indicating that CCSDD might be a therapeutic alternative to treat a variety of intractable posterior segment diseases.

Insulin-loaded PLGA microspheres for glucose-responsive release

Porous poly(lactic-co-glycolic acid) (PLGA) microspheres were prepared, loaded with insulin, and then coated in poly(vinyl alcohol) (PVA) and a novel boronic acid-containing copolymer [poly(acrylamide phenyl boronic acid-co-N-vinylcaprolactam); p(AAPBA-co-NVCL)]. Multilayer microspheres were generated using a layer-by-layer approach depositing alternating coats of PVA and p(AAPBA-co-NVCL) on the PLGA surface, with the optimal system found to be that with eight alternating layers of each coating. The resultant material comprised spherical particles with a porous PLGA core and the pores covered in the coating layers. Insulin could successfully be loaded into the particles, with loading capacity and encapsulation efficiencies reaching 2.83 ± 0.15 and 82.6 ± 5.1% respectively, and was found to be present in the amorphous form. The insulin-loaded microspheres could regulate drug release in response to a changing concentration of glucose. In vitro and in vivo toxicology tests demonstrated that they are safe and have high biocompatibility. Using the multilayer microspheres to treat diabetic mice, we found they can effectively control blood sugar levels over at least 18 days, retaining their glucose-sensitive properties during this time. Therefore, the novel multilayer microspheres developed in this work have significant potential as smart drug-delivery systems for the treatment of diabetes.

Dexamethasone distribution characteristic following controllable continuous sub-tenon drug delivery in rabbit

Drug delivery systems are required to be safe, minimally invasive and effectively delivery drug to the target tissues. But delivery drugs to the eye has not yet satisfied this need. Here, we focused on examining the distribution of dexamethasone (DEX) in ocular and plasmic samples following controllable continuous sub-Tenon drug delivery (CCSDD) of dexamethasone disodium phosphate (DEXP) in rabbit, and to compare that with two traditional routes: subconjunctival injection and intravenous injection. The DEX concentration was analyzed by Shimadzu LC-MS 2010 system. In CCSDD group, during observed 24 h, the mean DEX level in collected samples from highest to lowest following in order: sclera, cornea, retina/choroid, iris, plasma, aqueous humor, lens and vitreous body. In ocular solid tissue, the DEX level in posterior segment is higher than in anatomic corresponding anterior segment, but it is opposite in ocular fluid tissue. High levels of DEX were maintained at 12 h in the ocular tissue immediately after the administration. Even at 24 h, the mean DEX concentration was 31.72 ng/ml and 22.40 ng/ml in aqueous and vitreous, respectively. In CCSDD group, the ocular DEX exposure (AUC0-24) is much higher and plasma exposure is much less than IV group, and it is also similar in SC group except iris. The amount of DEX levels are markedly increased in ocular tissues but it yield lower plasma levels indicating reduction of systemic absorption by CCSDD. Thus, CCSDD is an effective method of delivering DEX into anterior and posterior segment of the eye.

Effective improvement of the neuroprotective activity after spinal cord injury by synergistic effect of glucocorticoid with biodegradable amphipathic nanomicelles

Dexamethasone acetate (DA) produces neuroprotective effects by inhibiting lipid peroxidation and inflammation by reducing cytokine release and expression. However, its clinical application is limited by its hydrophobicity, low biocompatibility and numerous side effects when using large dosage. Therefore, improving DA's water solubility, biocompatibility and reducing its side effects are important goals that will improve its clinical utility. The objective of this study is to use a biodegradable polymer as the delivery vehicle for DA to achieve the synergism between inhibiting lipid peroxidation and inflammation effects of the hydrophobic-loaded drugs and the amphipathic delivery vehicle. We successfully prepared DA-loaded polymeric micelles (DA/MPEG-PCL micelles) with monodispersed and approximately 25 nm in diameter, and released DA over an extended period in vitro. Additionally, in the hemisection spinal cord injury (SCI) model, DA micelles were more effective in promoting hindlimb functional recover, reducing glial scar and cyst formation in injured site, decreasing neuron lose and promoting axon regeneration. Therefore, our data suggest that DA/MPEG-PCL micelles have the potential to be applied clinically in SCI therapy.

Posterior drug delivery via periocular route: challenges and opportunities

Drug delivery to the posterior segment via the periocular route is a promising route for delivery of a range of formulations. In this review, we have highlighted the challenges and opportunities of posterior segment drug delivery via the periocular route. Consequently, we have discussed different types of periocular routes, physiological barriers that limit effective drug delivery, practical challenges regarding patient compliance and acceptability and recent advances in developing innovative strategies to enhance periocular drug delivery. We conclude with a perspective on how we envisage the importance of understanding complex barrier functions so as to continue to develop innovative drug-delivery systems.

Vitreous substitutes: challenges and directions

The natural vitreous body has a fine structure and complex functions. The imitation of the natural vitreous body by vitreous substitutes is a challenging work for both researchers and ophthalmologists. Gases, silicone oil, heavy silicone oil and hydrogels, particularly the former two vitreous substitutes are clinically widely used with certain complications. Those, however, are not real artificial vitreous due to lack of structure and function like the natural vitreous body. This article reviews the situations, challenges, and future directions in the development of vitreous substitutes, particularly the experimental and clinical use of a new artificial foldable capsular vitreous body.

Preparation and characterization of pullulanase debranched starches and their properties for drug controlled-release

Linear short amylose and glucan tend to align and aggregate to form hydrogels that hold less water. The drug release properties of debranched starch based tablets can be controlled by the pullulanase modification conditions.

In vitro and in vivo release characteristics of Tacrolimus (FK506) from an episcleral drug-delivery implant

PURPOSE

To investigate the in vitro and in vivo release characteristics of Tacrolimus (FK506) from an episcleral drug-delivery implant.

METHODS

For in vitro experiments, Tacrolimus-loaded implants (0.5 mL; at concentrations of 0.25, 0.5, and 1.0 mg/mL) were immersed in a balanced salt solution. Samples of the surrounding liquid were aspirated at different times over a 96-h period. For in vivo experiments, the experimental group received an implant loaded with Tacrolimus (0.5 mg/mL; 0.5 mL); the control group was given a subconjunctival injection of 0.5 mL Tacrolimus (0.5 mg/mL). On postoperative days 3, 7, 14, 28, and 56, 3 animals were sacrificed, and their eyes were enucleated. Tacrolimus concentrations were determined by liquid chromatographic-tandem mass spectrometry. Ocular toxicity was evaluated by slit-lamp photography, fundus photography, intraocular pressure (IOP), and histology.

RESULTS

The implants released Tacrolimus in a biphasic pattern for 96 h in the in vitro study. The release kinetics were not dependent on the drug concentrations. The in vivo study showed statistically significant differences between the 2 treatment groups. Tacrolimus levels were particularly high in the conjunctiva, iris, ciliary body, cornea, sclera, choroid, and retina in the experimental group, while concentrations were low and only lasted for 1 week in the controls. Slit-lamp photography, fundus photography, IOP, and histology showed no evidence of toxic effects.

CONCLUSIONS

The episcleral drug-delivery implant mechanically released Tacrolimus through the apertures of capsules and, consequently, may be a promising drug vehicle for the treatment of immune-mediated ocular disorders.