Pharmacokinetics of triamcinolone acetonide for the treatment of macular edema

Long-term outcomes of administration of intravitreal triamcinolone acetonide after posterior vitreous detachment during pars plana vitrectomy for proliferative diabetic retinopathy

AIM

To evaluate the long-term outcomes of intravitreal triamcinolone acetonide (TA) administration after posterior vitreous detachment (PVD) during pars plana vitrectomy (PPV) for patients with proliferative diabetic retinopathy (PDR).

METHODS

A total of 189 eyes (152 patients) who underwent PPV for severe PDR were reviewed. Intravitreal injection of TA (IVTA) was administered during PPV in 118 eyes (PPV+IVTA group), and 71 eyes did not receive IVTA (PPV group). Immediately after PVD, when most of the vitreous and proliferative membranes were removed, 0.1 mL TA (40 mg/mL) was injected into the vitreous cavity in the PPV+IVTA group. All patients were followed-up for least 12 months. Visual outcomes and postoperative complications were recorded and compared between the two groups.

RESULTS

IVTA was helpful for proliferative membrane peeling and haemostasis during PPV. In the PPV+IVTA group, best-corrected visual acuity had significantly improved and the intraocular pressure was controlled well during the follow-up. The incidence of early recurrent vitreous haemorrhage after PPV was significantly lower in the PPV+IVTA group (1.7%) than in the PPV group (9.9%) (p=0.028).

CONCLUSION

The administration of IVTA after PVD during PPV can effectively improve the final visual outcomes and prevent postoperative complications in patients with severe PDR.

Nanocarriers for the Delivery of Neuroprotective Agents in the Treatment of Ocular Neurodegenerative Diseases

Retinal neurodegeneration is considered an early event in the pathogenesis of several ocular diseases, such as diabetic retinopathy, age-related macular degeneration, and glaucoma. At present, there is no definitive treatment to prevent the progression or reversal of vision loss caused by photoreceptor degeneration and the death of retinal ganglion cells. Neuroprotective approaches are being developed to increase the life expectancy of neurons by maintaining their shape/function and thus prevent the loss of vision and blindness. A successful neuroprotective approach could prolong patients' vision functioning and quality of life. Conventional pharmaceutical technologies have been investigated for delivering ocular medications; however, the distinctive structural characteristics of the eye and the physiological ocular barriers restrict the efficient delivery of drugs. Recent developments in bio-adhesive in situ gelling systems and nanotechnology-based targeted/sustained drug delivery systems are receiving a lot of attention. This review summarizes the putative mechanism, pharmacokinetics, and mode of administration of neuroprotective drugs used to treat ocular disorders. Additionally, this review focuses on cutting-edge nanocarriers that demonstrated promising results in treating ocular neurodegenerative diseases.

A pilot study of viscoelastic agent to prevent recurrent vitreous hemorrhage after vitrectomy for proliferative diabetic retinopathy

BACKGROUND

To evaluate the possibilty of preventing recurrent vitreous hemorrhage (RVH) after vitrectomy in proliferative diabetic retinopathy (PDR) patients with unabsorbed vitreous hemorrhage (VH) by intravitreal injection of viscoelastic agent (VA) at the end of the surgery and compared its effect with triamcinolone acetonide (TA).

METHODS

This was a pilot prospective, observational study. PDR patients with VH who underwent vitrectomy were assigned to 3 groups according to the tamponade applicated at the end of the surgery, including VA group (intravitreally injected 1 ml VA if the retina was prone to bleed during the operation), TA group (intravitreally injected 2 mg TA when there was much exudates), or balanced salt solution (BSS) group (no tamponade). Then postoperative follow-up was performed routinely until 6 months after surgery. The primary outcome was the incidence of RVH, secondary outcome were the best-corrected visual acuity (BCVA) and introcular pressure (IOP). Cataract formation and other complication were also assessed.

RESULTS

A total of 68 eyes, from 68 patients, were included. 18,18,32 eyes were enrolled in the VA group, TA group and BSS group, respectively. The integral incidence of RVH after vitrectomy was 5.6%, 5.6% and 12.5% respectively (P = 0.602). There was no early RVH in VA or TA group, whereas 3 early RVHs were identified in BSS group, however there was no significant difference (P = 0.171). Every group had one late RVH case. In all groups, final BCVA showed significant improvement compared to baseline. BCVA at any postoperative visit showed no significant differences among 3 groups. Mean IOP was higher 1 week after surgery in VA group compared with the other groups; however, in other times the differences were not significant. No cataract formation and other complication was noted in 3 groups.

CONCLUSION

Intravitreal injection of VA or TA at the end of vitrectomy for PDR patients with unabsorbed VH tend to reduce the incidence of early RVH after vitrectomy similarly. As VA was preferred to applicate in the eyes that were prone to bleed, intravitreal injection of VA at the end of vitrectomy might be a promising method for preventing RVH in PDR patients.

Pharmacology of Corticosteroids for Diabetic Macular Edema

Purpose

Corticosteroids remain the mainstay of treatment for inflammatory diseases almost 80 years after their first clinical use. Topical ophthalmic formulations of corticosteroids have been available to treat disease of the anterior segment of the eye, but the approval of corticosteroids to treat vitreoretinal diseases, including vein occlusion, diabetic macular edema, and uveitis, has occurred only recently. Although most diseases respond to corticosteroid therapy, some patients are resistant to this therapy and side effects, including cataract and elevated intraocular pressure, can limit their use. The purpose of this review is to detail the basic science of corticosteroids focusing on differences in potency, drug delivery, pharmacokinetics, and gene activation, and how these differences affect safety and efficacy in the treatment of diabetic macular edema.

Methods

A review was conducted of basic science and pharmacology of the corticosteroids used to treat diabetic macular edema.

Results

Clinically available corticosteroids not only have differing potency and pharmacokinetics, but also activate different genes in different target tissues. These differences are associated with distinct efficacy, pharmacokinetic, and safety profiles. It is important to understand these differences in selecting corticosteroids to treat diabetic macular edema.

Conclusions

Recent advances in our understanding of the basic science of corticosteroids can explain clinical differences in these agents regarding efficacy and safety. Importantly, this understanding should allow the future discovery of additional novel corticosteroids to treat diabetic macular edema.

Principles of pharmacology in the eye

The eye is a highly specialized organ that is subject to a huge range of pathology. Both local and systemic disease may affect different anatomical regions of the eye. The least invasive routes for ocular drug administration are topical (e.g. eye drops) and systemic (e.g. tablets) formulations. Barriers that subserve as protection against pathogen entry also restrict drug permeation. Topically administered drugs often display limited bioavailability due to many physical and biochemical barriers including the pre-corneal tear film, the structure and biophysiological properties of the cornea, the limited volume that can be accommodated by the cul-de-sac, the lacrimal drainage system and reflex tearing. The tissue layers of the cornea and conjunctiva are further key factors that act to restrict drug delivery. Using carriers that enhance viscosity or bind to the ocular surface increases bioavailability. Matching the pH and polarity of drug molecules to the tissue layers allows greater penetration. Drug delivery to the posterior segment is a greater challenge and, currently, the standard route is via intravitreal injection, notwithstanding the risks of endophthalmitis and retinal detachment with frequent injections. Intraocular implants that allow sustained drug release are at different stages of development. Novel exciting therapeutic approaches include methods for promoting transscleral delivery, sustained release devices, nanotechnology and gene therapy.

Controlled Release of Dexamethasone From an Intravitreal Delivery System Using Porous Silicon Dioxide

PURPOSE

The current study aims to evaluate a porous silicon-based drug delivery system meant for sustained delivery of dexamethasone (Dex) to the vitreous and retina.

METHODS

Dexamethasone was grafted covalently into the pore walls of fully oxidized porous silicon particles (pSiO2-COO-Dex), which then was evaluated for the pharmacological effect of the payload on cultured ARPE19 cells before intravitreal injection. The Dex release profile was investigated in a custom designed dynamic dissolution chamber to mimic the turnover of vitreous fluid in rabbit eyes. Ocular safety, in vivo release, and pharmacodynamics were evaluated in rabbit eyes, and the human VEGF-induced rabbit retinal vascular permeability model.

RESULTS

Loading efficiency of Dex was 69 ± 9 μg per 1 mg of the pSiO2-COO-Dex particles. Dynamic in vitro release demonstrated a sustained mode when compared to free Dex, with the drug half-life extended by 5 times. The released Dex was unaltered and biologically active. In vivo drug release in rabbit eyes revealed a mode similar to the release seen in vitro, with a vitreous half-life of 11 days. At 2 and 4 weeks after a single intravitreal injection of pSiO2-COO-Dex particles (mean 2.71 ± 0.47 mg), intravitreal 500 ng of VEGF did not induce significant retinal vessel dilation or fluorescein leakage, while these events were observed in the eyes injected with empty pSiO2 particles or with free Dex. The retinal vessel score from fluorescein angiography for the control eyes was double the score for the eyes injected with pSiO2-COO-Dex. No adverse reaction was observed for the eyes injected with drug-loaded pSi particles during the course of the study.

CONCLUSIONS

The porous silicon-based Dex delivery system (pSiO2-COO-Dex) can be administered safely into vitreous without toxicity. Dex release from the porous silicon particles was sustained for 2 months and was effective against VEGF-induced retinal vessel reaction.

The PK-Eye: A Novel In Vitro Ocular Flow Model for Use in Preclinical Drug Development

A 2-compartment in vitro eye flow model has been developed to estimate ocular drug clearance by the anterior aqueous outflow pathway. The model is designed to accelerate the development of longer-acting ophthalmic therapeutics. Dye studies show aqueous flow is necessary for a molecule injected into the vitreous cavity to clear from the model. The clearance times of proteins can be estimated by collecting the aqueous outflow, which was first conducted with bevacizumab using phosphate-buffered saline in the vitreous cavity. A simulated vitreous solution was then used and ranibizumab (0.5 mg) displayed a clearance time of 8.1 ± 3.1 days, which is comparable to that observed in humans. The model can estimate drug release from implants or the dissolution of suspensions as a first step in their clearance mechanism, which will be the rate-limiting step for the overall resident time of a candidate dosage form in the vitreous. A suspension of triamcinolone acetonide (Kenalog®) (4.0 mg) displayed clearance times spanning 26-28 days. These results indicate that the model can be used to determine in vitro-in vivo correlations in preclinical studies to develop long-lasting therapeutics to treat blinding diseases at the back of the eye.

The impact of triamcinolone acetonide in early breast capsule formation in a rabbit model

BACKGROUND

The etiology and clinical treatment of capsular contracture remain unresolved as the causes may be multifactorial. Triamcinolone acetonide applied in the pocket during surgery was reported to be ineffective in prevention of capsular contracture. However, if injected 4-6 weeks after surgery or as a treatment for capsular contracture, decreased applanation tonometry measurements and pain were observed. It was assumed that intraoperative application of triamcinolone was not effective because its effect does not last long enough. However, betadine, antibiotics, and fibrin were found to be effective in preventing capsular contracture with intraoperative applications and are more effective in the early phases of wound healing than in later stages. The role of triamcinolone acetonide in capsule formation is unknown. The purpose of this study was to determine if triamcinolone acetonide modulates breast capsule formation or capsular contracture in the early phases of wound healing in a rabbit model.

METHODS

Rabbits (n=19) were implanted with one tissue expander and two breast implants and were killed at 4 weeks. Implant pocket groups were (1) Control (n=10) and (2) Triamcinolone (n=9). Pressure/volume curves and histological, immunological, and microbiological evaluations were performed. Operating room air samples and contact skin samples were collected for microbiological evaluation.

RESULTS

In the triamcinolone group, a decreased capsular thickness, mild and mononuclear inflammation, and negative or mild angiogenesis were observed. There were no significant differences in intracapsular pressure, fusiform cell density, connective tissue, organization of collagen fibers, and microbiological results between the groups. There was no significant difference in the dialysate levels of IL-8 and TNF-α, but correlation between IL-8 and TNF-α was observed.

CONCLUSION

Triamcinolone acetonide during breast implantation influences early capsule formation and may reduce capsular contracture.

LEVEL OF EVIDENCE III

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