Visual and anatomic outcomes associated with posterior segment complications after ganciclovir implant procedures in patients with AIDS and cytomegalovirus retinitis

Trans-corneal drug delivery strategies in the treatment of ocular diseases

The cornea is a remarkable tissue that possesses specialized structures designed to safeguard the eye against foreign objects. However, its unique properties also make it challenging to deliver drugs in a non-invasive manner. This review highlights recent advancements in achieving highly efficient drug transport across the cornea, focusing on nanomaterials. We have classified these strategies into three main categories based on their mechanisms and have analyzed their success and limitations in a systematic manner. The purpose of this review is to examine potential general principles that could improve drug penetration through the cornea and other natural barriers in the eye. We hope it will inspire the development of more effective drug delivery systems that can better treat ocular diseases.

Polymer based sustained drug delivery to the ocular posterior segment: barriers and future opportunities for the treatment of neovascular pathologies

There is an increasing momentum in research and pharmaceutical industry communities to design sustained, non-invasive delivery systems to treat chronic neovascular ocular diseases that affect the posterior segment of the eye including age-related macular degeneration and diabetic retinopathy. Current treatments include VEGF blockers, which have revolutionized the standard of care for patients, but their maximum therapeutic benefit is hampered by the need for recurrent and invasive administration procedures. Currently approved delivery systems intended to address these limitations exploit polymer technology to regulate drug release in a sustained manner. Here, we critically review sustained drug delivery approaches for the treatment of chronic neovascular diseases affecting the ocular posterior segment, with a special emphasis on novel and polymeric technologies spanning the spectrum of preclinical and clinical investigation, and those approved for treatment. The mechanism by which each formulation imparts sustained release, the impact of formulation characteristics on release and foreign body reaction, and special considerations related to the translation of these systems are discussed.

Implantable Drug Delivery Systems and Foreign Body Reaction: Traversing the Current Clinical Landscape

Precise delivery of therapeutics to the target structures is essential for treatment efficiency and safety. Drug administration via conventional routes requires overcoming multiple transport barriers to achieve and maintain the local drug concentration and commonly results in unwanted off-target effects. Patients’ compliance with the treatment schedule remains another challenge. Implantable drug delivery systems (IDDSs) provide a way to solve these problems. IDDSs are bioengineering devices surgically placed inside the patient’s tissues to avoid first-pass metabolism and reduce the systemic toxicity of the drug by eluting the therapeutic payload in the vicinity of the target tissues. IDDSs present an impressive example of successful translation of the research and engineering findings to the patient’s bedside. It is envisaged that the IDDS technologies will grow exponentially in the coming years. However, to pave the way for this progress, it is essential to learn lessons from the past and present of IDDSs clinical applications. The efficiency and safety of the drug-eluting implants depend on the interactions between the device and the hosting tissues. In this review, we address this need and analyze the clinical landscape of the FDA-approved IDDSs applications in the context of the foreign body reaction, a key aspect of implant–tissue integration.

Posterior Segment Ophthalmic Drug Delivery: Role of Muco-Adhesion with a Special Focus on Chitosan

Posterior segment eye diseases (PSEDs) including age macular degeneration (AMD) and diabetic retinopathy (DR) are amongst the major causes of irreversible blindness worldwide. Due to the numerous barriers encountered, highly invasive intravitreal (IVT) injections represent the primary route to deliver drugs to the posterior eye tissues. Thus, the potential of a more patient friendly topical route has been widely investigated. Mucoadhesive formulations can decrease precorneal clearance while prolonging precorneal residence. Thus, they are expected to enhance the chances of adherence to corneal and conjunctival surfaces and as such, enable increased delivery to the posterior eye segment. Among the mucoadhesive polymers available, chitosan is the most widely explored due to its outstanding mucoadhesive characteristics. In this review, the major PSEDs, their treatments, barriers to topical delivery, and routes of topical drug absorption to the posterior eye are presented. To enable the successful design of mucoadhesive ophthalmic drug delivery systems (DDSs), an overview of mucoadhesion, its theory, characterization, and considerations for ocular mucoadhesion is given. Furthermore, chitosan-based DDs that have been explored to promote topical drug delivery to the posterior eye segment are reviewed. Finally, challenges of successful preclinical to clinical translation of these DDSs for posterior eye drug delivery are discussed.

A Review of Ocular Drug Delivery Platforms and Drugs for Infectious and Noninfectious Uveitis: The Past, Present, and Future

Uveitis refers to a broad group of inflammatory disorders of the eye that often require medical and surgical management to improve or stabilize vision and prevent vision-threatening pathological changes to the eye. Drug delivery to the eye to combat inflammation and subsequent complications from uveitic conditions is complex as there are multiple barriers to absorption limiting availability of the needed drug in the affected tissues. As such, there has been substantial interest in developing new drugs and drug delivery platforms to help reduce intraocular inflammation and its complications. In this review, we discuss the challenges of drug delivery, novel technologies recently approved for uveitis patient care and promising drug delivery platforms for uveitis and sequelae of ocular inflammation.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part I: Biomaterials-Based Drug Delivery Devices

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 years old people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting of intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, the development of biomaterials-based approaches for a personalized and controlled delivery of therapeutic drugs and biomolecules represents the main challenge for the defeat of this neurodegenerative disease. Here we present a critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In the first part we expose the physiological and clinical aspects of the disease, focusing on the multiple factors that give origin to the disorder and highlighting the contribution of these factors to the triggering of each step of the disease. Then we analyze available and under development biomaterials-based drug-delivery devices (DDD), taking into account the anatomical and functional characteristics of the healthy and ill retinal tissue.

Advances in ocular drug delivery systems

Recent advances in pharmacological agents have led to successful treatment of a variety of retinal diseases such as neovascular age-related macular degeneration (AMD), diabetic macular oedema (DMO), and retinal vascular occlusions (RVO). These treatments often require repeated drug injections for an extended period of time. To reduce these repeated treatment burdens, minimally invasive drug delivery systems are needed. An ideal therapy should maintain effective levels of drug for the intended duration of treatment following a single application, recognising that a significant number of months of therapy may be required. There are numerous approaches under investigation to improve treatment options. This review will highlight the advantages and limitations of selected drug delivery systems of novel biomaterial implants and depots. The main emphasis will be placed on less invasive, longer acting, sustained release formulations for the treatment of retinal disorders.

Endophthalmitis in HIV Infection

Purpose: The role of HIV infection in exogenous and endogenous endophthalmitis has not been clarified. We aim to assess the potential role of HIV as a risk factor or a poor prognostic feature in this sight-threatening condition. Methods: Literature review. Review of evidence: Evidence for endophthalmitis in HIV patients is based on scarce retrospective case series and case reports. Infrequency of literature on this topic is owed to the diversity of the different types of endophthalmitis as well as the rarity of the coexistence of the two conditions. Conclusions: Endophthalmitis in HIV patients are a rare but potentially devastating condition. Many forms of endophthalmitis tend to occur in severely immunosuppressed HIV patients with low CD4 counts. Therefore, the early introduction of cART with full immune reconstitution is an essential part of the prevention of endophthalmitis in the HIV population.

Recent advances in intraocular sustained-release drug delivery devices

Topical eye-drop administration and intravitreal injections are the current standard for ocular drug delivery. However, patient adherence to the drug regimen and insufficient administration frequency are well-documented challenges to this field. In this review, we describe recent advances in intraocular implants designed to deliver therapeutics for months to years, to obviate the issues of patient adherence. We highlight recent advances in monolithic ocular implants in the literature, the commercialization pipeline, and approved for the market. We also describe design considerations based on material selection, active pharmaceutical ingredient, and implantation site.

MEMS devices for drug delivery

Novel drug delivery systems based on microtechnology have advanced tremendously, but yet face some technological and societal hurdles to fully achieve their potential. The novel drug delivery systems aim to deliver drugs in a spatiotemporal- and dosage-controlled manner with a goal to address the unmet medical needs from oral delivery and hypodermic injection. The unmet needs include effective delivery of new types of drug candidates that are otherwise insoluble and unstable, targeted delivery to areas protected by barriers (e.g. brain and posterior eye segment), localized delivery of potent drugs, and improved patient compliance. After scrutinizing the design considerations and challenges associated with delivery to areas that cannot be efficiently targeted through standard drug delivery (e.g. brain, posterior eye segment, and gastrointestinal tract), this review provides a summary of recent advances that addressed these challenges and summarizes yet unresolved problems in each target area. The opportunities for innovation in devising the novel drug delivery systems are still high; with integration of advanced microtechnology, advanced fabrication of biomaterials, and biotechnology, the novel drug delivery is poised to be a promising alternative to the oral administration and hypodermic injection for a large spectrum of drug candidates.

Topical ocular delivery to laser-induced choroidal neovascularization by dual internalizing RGD and TAT peptide-modified nanoparticles

A nanoparticle (NP) was developed to target choroidal neovascularization (CNV) via topical ocular administration. The NPs were prepared through conjugation of internalizing arginine-glycine-aspartic acid RGD (iRGD; Ac-CCRGDKGPDC) and transactivated transcription (TAT) (RKKRRQRRRC) peptide to polymerized ethylene glycol and lactic-co-glycolic acid. The iRGD sequence can specifically bind with integrin α_vβ₃, while TAT facilitates penetration through the ocular barrier. ¹H nuclear magnetic resonance and high-performance liquid chromatography demonstrated that up to 80% of iRGD and TAT were conjugated to poly(ethylene glycol)– poly(lactic-co-glycolic acid). The resulting particle size was 67.0±1.7 nm, and the zeta potential of the particles was −6.63±0.43 mV. The corneal permeation of iRGD and TAT NPs increased by 5.50- and 4.56-fold compared to that of bare and iRGD-modified NPs, respectively. Cellular uptake showed that the red fluorescence intensity of iRGD and TAT NPs was highest among primary NPs and iRGD- or TAT-modified NPs. CNV was fully formed 14 days after photocoagulation in Brown Norway (BN) rats as shown by optical coherence tomography and fundus fluorescein angiography analyses. Choroidal flat mounts in BN rats showed that the red fluorescence intensity of NPs followed the order of iRGD and TAT NPs > TAT-modified NPs > iRGD-modified NPs > primary NPs. iRGD and TAT dual-modified NPs thus displayed significant targeting and penetration ability both in vitro and in vivo, indicating that it is a promising drug delivery system for managing CNV via topical ocular administration.

Management of retinoblastoma: opportunities and challenges

Nano-delivery systems have significantly evolved over the last decade for the treatment of cancer by enabling site-specific delivery and improved bioavailability. The widely investigated nanoparticle systems are biodegradable polyesters, dendrimers, liposomes, mesoporous silica and gold nanoparticles. These particles when conjugated with different targeting motifs enhance the therapeutic efficiency of the drug molecules and biocompatibility. However, the application of such systems towards the treatment of retinoblastoma (RB), a rapidly spreading childhood eye cancer, still remains in its infancy. Nanoparticle-based systems that have been investigated for RB therapy have displayed improved drug delivery to the most restricted posterior segment of the eyes and have increased intra-vitreal half-life of the chemotherapy agents highlighting its potential in treatment of this form of cancer. This review focuses on the challenges involved in the treatment of RB and highlights the attempts made to develop nano-dimensional systems for the treatment of RB.

Polymeric formulations for drug release prepared by hot melt extrusion: application and characterization

Over the past few decades hot melt extrusion (HME) has emerged as a powerful processing technology for the production of pharmaceutical solid dosage forms in which an active pharmaceutical ingredient (API) is dispersed into polymer matrices. It has been shown that formulations using HME can provide time-controlled, sustained and targeted drug delivery, and improved bioavailability of poorly soluble drugs. In this review, the basic principles of the HME process are described together with an overview of some of the most common biodegradable and nonbiodegradable polymers used for the preparation of different formulations using this method. Further, the applications of HME in drug delivery and analytical techniques employed to characterize HME products are addressed.

Advances in ocular drug delivery: emphasis on the posterior segment

INTRODUCTION

Recent advances in pharmacological therapies to treat ocular diseases such as glaucoma, age-related macular degeneration, diabetic macular edema and retinal vascular occlusions have greatly improved the prognosis for these diseases. Due to these advances in pharmacological therapy, there is a great deal of interest in minimally invasive delivery methods, which has generated rapid developments in the field of ocular drug delivery.

AREAS COVERED

This review will summarize currently available and recent developments for ocular drug delivery to both the anterior and posterior segments. Modes of delivery, including topical, systemic, transcleral/periocular and intravitreal, will be discussed and corresponding examples will be given. This review will highlight the advantages and disadvantages of each mode of delivery and discuss strategies to address these issues.

EXPERT OPINION

An ideal therapy should maintain effective levels of drug for the intended duration of treatment following a single application, yet a significant number of months of therapy may be required. There are numerous approaches under investigation to improve treatment options. From the use of novel biomaterial implants and depots for sustained release, to prodrug formations, to iontophoresis to improve drug delivery, the main emphasis will continue to be placed on less invasive, longer acting, sustained release formulations in the treatment of numerous ocular disorders.

Drug delivery to the posterior segment of the eye for pharmacologic therapy

Treatment of diseases of the posterior segment of the eye, such as age-related macular degeneration, cytomegalovirus retinitis, diabetic retinopathy, posterior uveitis and retinitis pigmentosa, requires novel drug delivery systems that can overcome the many barriers for efficacious delivery of therapeutic drug concentrations. This challenge has prompted the development of biodegradable and nonbiodegradable sustained-release systems for injection or transplantation into the vitreous as well as drug-loaded nanoparticles, microspheres and liposomes. These drug delivery systems utilize topical, systemic, subconjunctival, intravitreal, transscleral and iontophoretic routes of administration. The focus of research has been the development of methods that will increase the efficacy of spatiotemporal drug application, resulting in more successful therapy for patients with posterior segment diseases. This article summarizes recent advances in the research and development of drug delivery methods of the posterior chamber of the eye, with an emphasis on the use of implantable devices as well as micro- and nanoparticles.

Drug delivery implants in the treatment of vitreous inflammation

The eye is a model organ for the local delivery of therapeutics. This proves beneficial when treating vitreous inflammation and other ophthalmic pathologies. The chronicity of certain diseases, however, limits the effectiveness of locally administered drugs. To maintain such treatments often requires frequent office visits and can result in increased risk of infection and toxicity to the patient. This paper focuses on the implantable devices and particulate drug delivery systems that are currently being implemented and investigated to overcome these challenges. Implants currently on the market or undergoing clinical trials include those made of nonbiodegradable polymers, containing ganciclovir, fluocinolone acetonide, triamcinolone acetonide, and ranibizumab, and biodegradable polymers, containing dexamethasone, triamcinolone acetonide, and ranibizumab. Investigational intravitreal implants and particulate drug delivery systems, such as nanoparticles, microparticles, and liposomes, are also explored in this review article.

Intravitreal devices for the treatment of vitreous inflammation

The eye is a well-suited organ for local delivery of therapeutics to treat vitreous inflammation as well as other pathologic conditions that induce visual loss. Several conditions are particularly challenging to treat and often require chronic courses of therapy. The use of implantable intravitreal devices for drug delivery is an emerging field in the treatment of vitreous inflammation as well as other ophthalmologic diseases. There are unique challenges in the design of these devices which include implants, polymers, and micro- and nanoparticles. This paper reviews current and investigational drug delivery systems for treating vitreous inflammation as well as other pathologic conditions that induce visual loss. The use of nonbiodegradable devices such as polyvinyl alcohol-ethylene vinyl acetate polymers and polysulfone capillary fibers, and biodegradable devices such as polylactic acid, polyglycolic acid, and polylactic-co-glycolic acid, polycaprolactones, and polyanhydrides are reviewed. Clinically used implantable devices for therapeutic agents including ganciclovir, fluocinolone acetonide, triamcinolone acetonide, and dexamethasone are described. Finally, recently developed investigational particulate drug delivery systems in the form of liposomes, microspheres, and nanoparticles are examined.

Intraocular corticosteroids for posterior segment disease: 2012 update

INTRODUCTION

Diabetic macular edema (DME), cystoid macular edema (CME), age-related macular degeneration (AMD), retinal vascular occlusion (RVO) and uveitis are responsible for severe visual impairment worldwide. In some patients with these conditions, treatment with intraocular corticosteroids may be beneficial. Although off-label use of these agents has occurred for many years, novel agents including preservative-free and sustained-release intravitreal implants are currently being studied in clinical trials (CTs).

AREAS COVERED

This paper reviews the use of CTs for vitreoretinal (VR) diseases including choroidal neovascularization, CME, DME, RVO and posterior uveitis. It also discusses the use of corticosteroids for treating VR disease, including dexamethasone, fluocinolone acetonide, intravitreal implants and triamcinolone acetonide.

EXPERT OPINION

Used alone, intravitreal corticosteroids may benefit disorders such as DME, RVO and uveitis compared with standard therapy. Cases of exudative AMD non-responsive to standard treatment may benefit from combination therapy, including usage of intravitreal corticosteroid injections. Intraoperative use of these agents may aid visualization of retinal structures. Sustained-release intraocular implants have been approved for posterior uveitis and RVO associated with macular edema. In spite of this, most intraocular corticosteroids have a limited duration of action along with significant side effects, including cataract and glaucoma. Currently, intravitreal corticosteroid usage for DME is considered off-label.

Intraocular pressure changes: an important determinant of the biocompatibility of intravitreous implants

BACKGROUND

In recent years, research efforts exploring the possibility of using biomaterial nanoparticles for intravitreous drug delivery has increased significantly. However, little is known about the effect of material properties on intravitreous tissue responses.

PRINCIPAL FINDINGS

To find the answer, nanoparticles made of hyaluronic acid (HA), poly (l-lactic acid) (PLLA), polystyrene (PS), and Poly N-isopropyl acrylamide (PNIPAM) were tested using intravitreous rabbit implantation model. Shortly after implantation, we found that most of the implants accumulated in the trabecular meshwork area followed by clearance from the vitreous. Interestingly, substantial reduction of intraocular pressure (IOP) was observed in eyes implanted with particles made of PS, PNIPAM and PLLA, but not HA nanoparticles and buffered salt solution control. On the other hand, based on histology, we found that the particle implantation had no influence on cornea, iris and even retina. Surprisingly, substantial CD11b+ inflammatory cells were found to accumulate in the trabecular meshwork area in some animals. In addition, there was a good relationship between recruited CD11b+ cells and IOP reduction.

CONCLUSIONS

Overall, the results reveal the potential influence of nanoparticle material properties on IOP reduction and inflammatory responses in trabecular meshwork. Such interactions may be critical for the development of future ocular nanodevices with improved safety and perhaps efficacy.

Intravitreal ganciclovir maintenance injection for cytomegalovirus retinitis: efficacy of a low-volume, intermediate-dose regimen

OBJECTIVE

To report the clinical outcomes of highly active antiretroviral therapy (HAART)-naïve, human immunodeficiency virus (HIV)-positive patients with newly diagnosed cytomegalovirus (CMV) retinitis receiving intravitreal injections of a low-volume intermediate maintenance dose (1.0 mg/0.02 ml) of ganciclovir.

DESIGN

Nonrandomized, retrospective, interventional series.

PARTICIPANTS

A consecutive cohort of 34 eyes from 24 HAART-naïve patients with AIDS and diagnosed with CMV retinitis by retinal specialists at the Singapore Communicable Disease Centre.

INTERVENTION

Patients received a maintenance dose of 1.0 mg/0.02 ml of intravitreal ganciclovir once weekly after standard induction therapy with 2.0 mg/0.04 ml of twice weekly intravitreal ganciclovir.

MAIN OUTCOME MEASURES

Time to progression, visual acuity, and complications. Progression was observed using photographic documentation.

RESULTS

The median time to progression was 152 days (mean, 380.1 days, 95% confidence interval, 240.8-519.4). The median follow-up was 95 days (mean, 207.9 days). Three eyes developed rhegmatogenous detachments, but there was no endophthalmitis after 1858 injections. Contralateral involvement of CMV retinitis occurred in 17.6% of the patients. The cost estimate for intravitreal injections over a 6-month period was 11.7% that of sustained-release implants for unilateral treatment and 11.1% that of daily continuous intravenous infusions and oral valganciclovir compared with bilateral treatments.

CONCLUSIONS

Weekly low-volume, intermediate-dose (1.0 mg/0.02 ml) ganciclovir is an efficacious option in developing countries where newer options of sustained-release implants and oral valganciclovir are unavailable or prohibitively expensive. The regimen maintains a long time to progression, preserving vision while minimizing retinal toxicity complications.

A review of implantable intravitreal drug delivery technologies for the treatment of posterior segment eye diseases

Intravitreal implantable device technology utilizes engineered materials or devices that could revolutionize the treatment of posterior segment eye diseases by affording localized drug delivery, responding to and interacting with target sites to induce physiological responses while minimizing side-effects. Conventional ophthalmic drug delivery systems such as topical eye-drops, systemic drug administration or direct intravitreal injections do not provide adequate therapeutic drug concentrations that are essential for efficient recovery in posterior segment eye disease, due to limitations posed by the restrictive blood-ocular barriers. This review focuses on various aspects of intravitreal drug delivery such as the impediment of the blood-ocular barriers, the potential sites or intraocular drug delivery device implantation, the various approaches employed for ophthalmic drug delivery and includes a concise critical incursion into specialized intravitreal implantable technologies for the treatment of anterior and posterior segment eye disease. In addition, pertinent future challenges and opportunities in the development of intravitreal implantable devices is discussed and explores their application in clinical ophthalmic science to develop innovative therapeutic modalities for the treatment of various posterior segment eye diseases. The inherent structural and functional properties, the potential for providing rate-modulated drug delivery to the posterior segment of the eye and specific development issues relating to various intravitreal implantable drug delivery devices are also expressed in this review.

The use of intraocular corticosteroids

BACKGROUND

Diabetic macular edema (DME), cystoid macular edema (CME), age-related macular degeneration (AMD), retinal vascular occlusion (RVO) and uveitis are responsible for severe visual impairment worldwide. In some patients with these conditions, treatment with intraocular corticosteroids may be beneficial. Although off-label use of these agents has occurred for many years, novel agents including preservative-free and sustained-release intravitreal implants are currently being studied in clinical trials (CTs).

OBJECTIVE

To review the use of intraocular corticosteroids.

METHODS

Literature review.

RESULTS

Used alone, intravitreal corticosteroids may benefit disorders such as DME, RVO and uveitis compared with standard therapy or observation. Patients with AMD may benefit more from combination treatment with photodynamic therapy, intravitreal corticosteroid and intravitreal anti-VEGF injections. Intraoperative use of these agents may assist in visualization and manipulation of fine retinal structures. Sustained-release intraocular implants have been approved for severe posterior uveitis, and have shown benefits in ongoing CTs.

CONCLUSION

Although intraocular corticosteroid injections have a limited duration of action requiring frequent re-treatment, and significant side effects including cataract and glaucoma development, intraocular injections may be of benefit in certain ocular disorders. Corticosteroid implants are emerging as potential treatments for macular edema due to uveitis, DME or RVO.

Nanoparticle-integrin antagonist C16Y peptide treatment of choroidal neovascularization in rats

Choroidal neovascularization (CNV) is the major cause of severe vision loss in patients with age-related macular degeneration (AMD). Present drug delivery may be limited by poor delivery to the choroid where CNV originates. The goal of this study was to develop a drug delivery system to deliver an integrin-antagonist peptide to the sub-retinal space. We developed polylactic acid/polylactic acid-polyethylene oxide nanoparticles (PLA/PLA-PEO) encapsulating the water-soluble integrin-antagonist peptide, C16Y (C16Y-NP). The PLA/PLA-PEO nanoparticles were 302+/-85.1 nm in size and demonstrated a two-week sustained release, in vitro, of encapsulated C16Y. Injected nanoparticles did not demonstrate retinal toxicity as determined by histopathology. C16Y peptide solution or C16Y-NP was injected 5 or 9 days post laser photocoagulation. A single intravitreal injection of C16Y peptide and C16Y-NP solution at both 5 days and 9 days post laser photocoagulation statistically inhibited CNV (p<0.05). However, for the day 5 injections the area of choroidal neovascularization on day 12 was smaller for C16Y-NP than for C16Y peptide solution (p<0.05) because of the short vitreous half-life of C16Y peptide solution. These results demonstrate the importance of sustained release delivery for the treatment of choroidal neovascularization associated with age-related macular degeneration. The intravitreally administered PLA/PLA-PEO containing coumarin was found to penetrate the retina and localize to the RPE. These results suggest that nanoparticles of biodegradable polymers may be a potential useful delivery system for intravitreal injection of drugs in the treatment of AMD.

Intraocular sustained-release delivery systems for triamcinolone acetonide

Recently, the use of triamcinolone acetonide (TA) injection has increased dramatically in treatment for several ocular diseases. Among them, macular diseases such as macular edema due to diabetic retinopathy, venous occlusive diseases, ocular inflammation and age-related macular degeneration (AMD) are very common vision threatening disorders and are great challenges to treat. In these types of chronic retinal diseases, repeated intraocular injections of TA are often required which increases the likelihood of complications. In order to achieve sustained-release, maintain therapeutic levels of TA over longer times and reduce frequency of intravitreal injections, researchers are investigating different implantable devices or injectable systems. However, as of yet, there is no sustained-release product for TA available on the commercial market. This review discusses and compares different sustained-release devices or injectable systems that are currently being developed.

Investigating the movement of intravitreal human serum albumin nanoparticles in the vitreous and retina

PURPOSE

To investigate the movement of intravitreally injected human serum albumin nanoparticles (HSA-NP) with respect to nanoparticle surface charge and retinal injury.

METHODS

HSA-NPs were developed by a desolvation technique. HSA-NPs were cationized by covalent coupling of hexamethylenediamine on the particle surface. Either anionic or cationic HSA-NPs were injected to determine the effect of surface charge on intravitreal nanoparticle movement. HSA-NPs were injected intravitreally into both normal and laser photocoagulated eyes to examine the effect of the integrity of retinal tissue on the retinal penetration. The retinal penetration of fluorescence labeled anionic HSA-NPs was investigated by confocal microscopy.

RESULTS

Anionic particles (-33.3+/-6.1 mV) more easily diffused through the 3-dimensional vitreal network of collagen fibrils than did their cationic counterparts (11.7+/-7.2 mV). In the laser photocoagulated retina, more HSA-NPs were detected in the choroidal space, compared to the normal retina. The immunohistochemical studies indicated that HSA-NPs were taken up into Müller cells.

CONCLUSIONS

The movement of intravitreal nanoparticles depended on both nanoparticles surface charge and retinal injury. The Müller cells might play an important role in the retinal penetration of nanoparticles. The anionic HSA-NP is a promising drug or gene delivery carrier to the sub-retinal space and RPE.

Sustained-release ophthalmic drug delivery systems for treatment of macular disorders: present and future applications

Macular disease currently poses the greatest threat to vision in aging populations. Historically, most of this pathology could only be dealt with surgically, and then only after much damage to the macula had already occurred. Current pathophysiological insights into macular diseases have allowed the development of effective new pharmacotherapies. The field of drug delivery systems has advanced over the last several years with emphasis placed on controlled release of drug to specific areas of the eye. Its unique location and tendency toward chronic disease make the macula an important and attractive target for drug delivery systems, especially sustained-release systems. This review evaluates the current literature on the research and development of sustained-release posterior segment drug delivery systems that are primarily intended for macular disease with an emphasis on age-related macular degeneration.Current effective therapies include corticosteroids and anti-vascular endothelial growth factor compounds. Recent successes have been reported using anti-angiogenic drugs for therapy of age-related macular degeneration. This review also includes information on implantable devices (biodegradable and non-biodegradable), the use of injected particles (microspheres and liposomes) and future enhanced drug delivery systems, such as ultrasound drug delivery. The devices reviewed show significant drug release over a period of days or weeks. However, macular disorders are chronic diseases requiring years of treatment. Currently, there is no 'gold standard' for therapy and/or drug delivery. Future studies will focus on improving the efficiency and effectiveness of drug delivery to the posterior chamber. If successful, therapeutic modalities will significantly delay loss of vision and improve the quality of life for patients with chronic macular disorders.

Novel approaches to retinal drug delivery

Research into treatment modalities affecting vision is rapidly progressing due to the high incidence of diseases such as diabetic macular edema, proliferative vitreoretinopathy, wet and dry age-related macular degeneration and cytomegalovirus retinitis. The unique anatomy and physiology of eye offers many challenges to developing effective retinal drug delivery systems. Historically, drugs have been administered to the eye as liquid drops instilled in the cul-de-sac. However retinal drug delivery is a challenging area. The transport of molecules between the vitreous/retina and systemic circulation is restricted by the blood-retinal barrier, which is made up of retinal pigment epithelium and endothelial cells of the retinal blood vessels. An increase in the understanding of drug absorption mechanisms into the retina from local and systemic administration has led to the development of various drug delivery systems, such as biodegradable and non-biodegradable implants, microspheres, nanoparticles and liposomes, gels and transporter-targeted prodrugs. Such diversity in approaches is an indication that there is still a need for an optimized noninvasive or minimally invasive drug delivery system to the eye. A number of large molecular weight compounds (i.e., oligonucleotides, RNA aptamers, peptides and monoclonal antibodies) have been and continue to be introduced as new therapeutic entities. However, for high molecular weight polar compounds the mechanism of epithelial transport is primarily through the tight junctions in the retinal pigment epithelium, as these agents undergo limited transcellular diffusion. Delivery and administration of these new drugs in a safe and effective manner is still a major challenge facing pharmaceutical scientists. In this review article, the authors discuss various drug delivery strategies, devices and challenges associated with drug delivery to the retina.

Drug delivery methods for posterior segment disease

PURPOSE OF REVIEW

New pharmacotherapies for posterior segment diseases of the eye have been recently introduced which use novel drug delivery methods. The various current and potential future methods will be discussed.

RECENT FINDINGS

Drug delivery systems have been developed which can provide controlled release of drug for potentially long periods of time. Ideal candidates for these devices are chronic conditions that require repeated local administration of drug, such as noninfectious intermediate or posterior uveitis, neovascular age-related macular degeneration, and persistent macular edema due to diabetic retinopathy or venous occlusive disease. Recently, Retisert (Bausch & Lomb, Rochester, New York, USA), a nonbiodegradable fluocinolone acetonide implant, was approved for use in noninfectious uveitis affecting the posterior segment and is currently in clinical trials for the treatment of macular edema. A biodegradable dexamethasone implant is currently in clinical trials for the treatment of uveitis and diabetic macular edema.

SUMMARY

With the development of therapeutic agents that require repeated administration comes a need for new strategies to improve safety and maximize efficacy. Novel drug delivery systems involving nonbiodegradable or biodegradable implants, microparticulates or nanoparticulates, liposomes, or transscleral iontophoresis may provide the solution.

Intraocular implants for extended drug delivery: therapeutic applications

An overview of ocular implants with therapeutic application potentials is provided. Various types of implants can be used as slow release devices delivering locally the needed drug for an extended period of time. Thus, multiple periocular or intraocular injections of the drug can be circumvented and secondary complications minimized. The various compositions of polymers fulfilling specific delivery goals are described. Several of these implants are undergoing clinical trials while a few are already commercialized. Despite the paramount progress in design, safety and efficacy, the place of these implants in our clinical therapeutic arsenal remains limited. Miniaturization of the implants allowing for their direct injection without the need for a complicated surgery is a necessary development avenue. Particulate systems which can be engineered to target specifically certain cells or tissues are another promising alternative. For ocular diseases affecting the choroid and outer retina, transscleral or intrasscleral implants are gaining momentum.

Vitreal pharmacokinetics of dipeptide monoester prodrugs of ganciclovir

PURPOSE

The aim of this study was to determine vitreal pharmacokinetics of a series of dipeptide monoester ganciclovir (GCV) prodrugs and to study their interaction with the retinal peptide transporter.

METHODS

New Zealand albino male rabbits were selected as the animal model. Ocular microdialysis technique was employed to delineate the pharmacokinetics of GCV, L-valine-GCV and dipeptide monoester GCV prodrugs (L-valine-L-valine, L-tyrosine-L-valine, and L-glycine- L-valine) following intravitreal administration.

RESULTS

Val-GCV and Val-Val-GCV inhibited retinal uptake of [3H]Gly-Sar by 43% and 37%, respectively, suggesting that these prodrugs may be substrates of the retinal peptide transport system. Val-GCV and Gly-Val-GCV were observed to be the most stable GCV prodrugs in vitreous humor. All GCV prodrugs were rapidly converted to GCV in retinal homogenates. Vitreal pharmacokinetic studies suggest that Val-GCV and Val-Val-GCV are rapidly eliminated from the vitreous chamber, compared to GCV, whereas Gly-Val-GCV is eliminated at a much slower rate. Retinal GCV concentrations generated from all three prodrugs, at the end of 5 h, were almost equivalent and were almost twice that following intravitreal administration of GCV. Gly-Pro, however, did not demonstrate any effect on retinal uptake of Val-GCV or Gly-Val-GCV.

CONCLUSIONS

Considering retinal GCV concentrations generated and vitreal pharmacokinetic profiles, Gly-Val-GCV appears to be a lead candidate for further in vivo evaluation against human cytomegalovirus (HCMV) retinitis.

Ocular morbidity associated with intravitreal triamcinolone acetonide

AIM

To report on the complications associated with the use of intravitreal triamcinolone acetonide (IVTA) in a tertiary referral hospital setting.

MATERIALS AND METHODS

A retrospective case series review of all IVTA injections carried out over a period of 30 months.

RESULTS

One hundred and thirty IVTA injections were performed; nine with limited local follow-up were excluded. Thus, 121 injections (108 patients, 114 eyes) were included in the study. Triamcinolone (4 mg) was used in all cases. Indications were diabetic macular oedema (n=41 eyes), retinal vein occlusions (n=27), postoperative cystoid macular oedema (n=24), exudative age-related macular degeneration (n=16), and others (n=6). No intraoperative complications were recorded. Postoperative intraocular pressure (IOP) readings of 22, 28, 35, and 40 mmHg or higher were recorded in 46.5, 29.8, 12.3, and 7.9% of eyes, respectively. IOP elevation was treated with antiglaucoma medication in all but one eye (0.9%) that required trabeculectomy and one (0.9%) that required vitrectomy with cataract extraction for suspected phacoanaphylactic glaucoma. Two eyes (1.8%) developed retinal detachment; both had previously been treated for retinal breaks. One eye (0.9%) developed culture-positive endophthalmitis.

CONCLUSIONS

Significant morbidity is associated with IVTA injection; clinicians should be aware when considering treatment options.

Drug delivery from ocular implants

Developing an intraocular drug delivery system (DDS) is urgently needed because most vitreoretinal diseases are refractory to conventional pharmacological approaches; eye drops and systemically administered drugs cannot deliver therapeutic drug concentrations into vitreoretinal tissue. Intraocular DDSs address this problem. Intraocular sustained-drug release via implantable devices or injectable microparticles has been investigated to treat vitreoretinal diseases. A nonbiodegradable implant was first used in 1996 for cytomegalovirus retinitis secondary to the acquired immunodeficiency syndrome. Biodegradable implants, composed of hydrophilic or hydrophobic polymers, in the shape of rods, plugs, discs or sheets have been investigated. An injectable rod is presently being assessed in a Phase III trial to treat macular oedema secondary to diabetic retinopathy or branch-retinal vein occlusion. Intraocular DDSs using a biodegradable implant may soon be successfully used to treat serious intraocular disorders.

Outcomes Associated with Ganciclovir Implants in Patients with AIDS-Related Cytomegalovirus Retinitis

PURPOSE

To investigate complications associated with ganciclovir implants used to treat AIDS-related cytomegalovirus (CMV) retinitis, and to identify factors that predict poor outcomes.

DESIGN

Retrospective chart review.

PARTICIPANTS

Consecutive patients with AIDS-related CMV retinitis from 3 clinical facilities who underwent implantation procedures during the period January 1, 1995 through December 31, 2001.

METHODS

Baseline for each patient was the date of the first implantation procedure performed during the study period by one of the facilities' surgeons (index implant). Medical and ophthalmological data were collected at baseline and at specific time points after baseline. The dates on which additional implantation procedures were performed and the dates on which complications or vision loss were identified were also recorded. Relationships between potential risk factors and outcomes were studied by Kaplan-Meier analyses and Cox proportional hazards regression models.

MAIN OUTCOME MEASURES

Primary outcome measures included postoperative complications specifically related to or possibly related to ganciclovir implants. A secondary outcome measure was vision loss after implantation procedures.

RESULTS

The charts of 174 patients (one study eye per patient; 279 implants) were reviewed. Median follow-up was 14.4 months (range, 0-7 years). Complications specifically related to implants occurred throughout follow-up at a rate of 0.064 events per patient-year. Complications possibly related to implants occurred at an overall rate of 0.377 per patient-year, but seemed to be more common during the first 2 years after baseline. During the first 2 years of follow-up, retinal detachments occurred at a rate of 0.156 events per patient-year. The cumulative risk of vision loss (> or =3 lines of Snellen visual acuity) at 7 years was 70%. Poor outcomes were associated with disease factors (size and activity of lesions), lack of highly active antiretroviral therapy (HAART), and lack of HAART-associated immune reconstitution, but not with surgical factors or implant-specific complications.

CONCLUSIONS

Complications specifically associated with ganciclovir implants can occur many years after implantation procedures, but the incidence of such complications is low. Continued vision loss is not attributable directly to complications of implants in most cases. This information will help in planning of treatment strategies for CMV retinitis in long-term survivors of human immunodeficiency virus disease.

Ganciclovir implant in the treatment of cytomegalovirus retinitis

The ganciclovir implant is a sustained-release intraocular drug delivery system used to treat cytomegalovirus retinitis that provides a high and steady-state concentration of the drug in the vitreous cavity over a period of 7-8 months. Randomized, controlled clinical trials have demonstrated a superior efficacy of the implant compared with intravenous ganciclovir. Severe adverse events associated with the implant are uncommon, though potentially blinding. In addition, the implant provides no protection against second-eye or visceral cytomegalovirus retinitis infections. This review summarizes the clinical indications for and complications associated with the ganciclovir implant.

Study of Ocular Transport of Drugs Released from an Intravitreal Implant Using Magnetic Resonance Imaging

Ensuring optimum delivery of therapeutic agents in the eye requires detailed information about the transport mechanisms and elimination pathways available. This knowledge can guide the development of new drug delivery devices. In this study, we investigated the movement of a drug surrogate, Gd-DTPA (Magnevist) released from a polymer-based implant in rabbit vitreous using T1-weighted magnetic resonance imaging (MRI). Intensity values in the MRI data were converted to concentration by comparison with calibration samples. Concentration profiles approaching pseudosteady state showed gradients from the implant toward the retinal surface, suggesting that diffusion was occurring into the retinal-choroidal-scleral (RCS) membrane. Gd-DTPA concentration varied from high values near the implant to lower values distal to the implant. Such regional concentration differences throughout the vitreous may have clinical significance when attempting to treat ubiquitous eye diseases using a single positional implant. We developed a finite element mathematical model of the rabbit eye and compared the MRI experimental concentration data with simulation concentration profiles. The model utilized a diffusion coefficient of Gd-DTPA in the vitreous of 2.8 x 10(-6) cm2 s(-1) and yielded a diffusion coefficient for Gd-DTPA through the simulated composite posterior membrane (representing the retina-choroidsclera membrane) of 6.0 x 10(-8) cm2 s(-1). Since the model membrane was 0.03-cm thick, this resulted in an effective membrane permeability of 2.0 x 10(-6) cm s(-1). Convective movement of Gd-DTPA was shown to have minimal effect on the concentration profiles since the Peclet number was 0.09 for this system.

Drug delivery systems for vitreoretinal diseases

The eye has an environment that is specific unto itself in terms of pharmacokinetics: the inner and outer blood-retinal barriers separate the retina and the vitreous from the systemic circulation and vitreous body, which physiologically has no cellular components, occupies the vitreous cavity, an inner space of the eye, and reduces practical convection of molecules. Considering this, development of a drug delivery system (DDS) is becoming increasingly important in the treatment of vitreoretinal diseases not only to facilitate drug efficacy but also to attenuate adverse effects. The DDS has three major goals: enhances drug permeation (e.g., iontophoresis and transscleral DDS), controls release of drugs (e.g., microspheres, liposomes, and intraocular implants), and targets drugs (e.g., prodrugs with high molecular weight and immunoconjugates). Comprehensive knowledge of these should lead to development of innovative treatment modalities.

Complications of ganciclovir implant surgery in patients with cytomegalovirus retinitis: the Ganciclovir Cidofovir Cytomegalovirus Retinitis Trial

PURPOSE

To describe the complications of ganciclovir implant surgery in patients with cytomegalovirus retinitis.

METHODS

Prospective data collection within the context of a randomized, controlled clinical trial, comparing a regimen of the ganciclovir implant plus oral ganciclovir to one of intravenous cidofovir for the treatment of cytomegalovirus retinitis in patients with AIDS. Adverse events were compared for patients undergoing implant surgery in the following groups: primary versus replacement implant surgery, inpatient versus outpatient surgery, and general versus local anesthesia.

RESULTS

Fifty-six eyes of 42 patients underwent a total of 74 ganciclovir implant surgeries. Vitreous hemorrhage was the most common adverse event, occurring in 10% of eyes undergoing surgery with local anesthesia but in no eyes undergoing surgery with general anesthesia. All vitreous hemorrhages resolved within 60 days. Patients in the general anesthesia and inpatient surgery groups tended to have a lower risk of complications in the first 30 days than did patients in the local anesthesia and outpatient surgery groups, but no differences in the complication rate were found after 60 days. Visual acuity was similar among these different groups. There were no cases of endophthalmitis.

CONCLUSION

Ganciclovir implant surgery in patients with AIDS and cytomegalovirus retinitis was associated with a low risk of serious complications in the first 60 days after surgery. Vitreous hemorrhage was the most commonly observed complication and resolved in all cases.

Posterior segment manifestations of HIV/AIDS

The ocular posterior segment manifestations of AIDS may be divided into four categories: retinal vasculopathy, unusual malignancies, neuro-ophthalmologic abnormalities, and opportunistic infections. Microvasculopathy is the most common manifestation. Opportunistic infections, particularly cytomegalovirus retinitis and progressive outer retinal necrosis, are the most likely to result in visual loss due to infection or subsequent retinal detachment. Diagnosis and treatment are guided by the particular conditions and immune status of the patient.

Endophthalmitis after ganciclovir implant in patients with AIDS and cytomegalovirus retinitis

PURPOSE

To describe the incidence, clinical course, and outcomes of endophthalmitis in patients treated with a ganciclovir implant.

DESIGN

Retrospective review of cases identified from a clinical survey.

METHODS

Cases of endophthalmitis were identified from a survey of 30 clinical practices known to treat a large number of patients with cytomegalovirus retinitis.

RESULTS

Twenty-four cases of endophthalmitis were identified from 5185 implants performed (incidence, 0.46%). Final visual acuity ranged from 20/20 to no light perception, with 50% (12/24) seeing light perception or worse. Vitreous cultures revealed Staphylococcus epidermidis in 29% (7/24) of patients, whereas other gram-positive organisms were responsible in 42% (10/24) of cases. In the remaining 29% (7/24) of cases, no organisms were cultured; these cases exhibited a better visual outcome (P =.007). Six of the eight late-onset cases were associated with wound problems such as implant strut or suture exposure. There was no significant relationship between implant removal and final visual acuity.

CONCLUSIONS

Endophthalmitis is an infrequent but potentially devastating complication associated with placement of a ganciclovir implant.

Ultrasound biomicroscopic study of sclerotomy sites after implantation of sustained release drug devices

BACKGROUND/AIMS

To evaluate the potential of ultrasound biomicroscopy (UBM) as a tool to study the precise location and changes of sclerotomy sites of the eye with an intraocular drug delivery device.

METHODS

Eight eyes of six patients (13 sites) who received ganciclovir implants were examined by UBM. Examinations were performed 1-26 months (mean 12.8 months) postoperatively. Serial transverse and radial sections of the anterior ciliary body around the sclerotomy sites were obtained.

RESULTS

The ganciclovir implant contour was successfully viewed using an UBM with high reflectivity. Three implants were deviated anteriorly and they were very close to the ciliary body and the lens (anterior deviation), while four implants were deviated posteriorly and away from the lens (posterior deviation). The other six implants were located at the appropriate position as intended. A solitary homogeneous mass with a medium reflectivity around the suture tab was observed at 12 out of 13 sites in seven eyes. Thick membranes extending from sclerotomy sites to the ora serrata were found at two sites in two eyes.

CONCLUSION

UBM is helpful in detecting abnormal manifestations around ganciclovir implants and is a valuable tool to assess the changes of the sclerotomy sites of the sustained released intraocular devices.

Noninvasive detection of ganciclovir in ocular tissue by Raman spectroscopy: implication for monitoring of drug release

Treatment of various pathological conditions in ophthalmology, such as cytomegalovirus (CMV) retinopathy and endophthalmitis, requires a local drug intervention rather than a systemic approach. Accurate knowledge of intraocular drug concentration can permit the ophthalmologist to maintain drug levels within the therapeutic levels necessary for an optimal prognosis, while preventing or minimizing toxicity associated with drug overdose.

PURPOSE

To develop a noninvasive/noncontact method for quantification of the local concentration of ganciclovir in the ocular media.

METHODS

An integrated CCD-based Raman spectroscopic system designed specifically for ophthalmic applications was used to noninvasively detect the presence of ganciclovir in the ocular media. Various known concentrations of ganciclovir were injected into the aqueous humor of rabbit eyes in a pilot study, in vivo. Raman spectra were then acquired by focusing an argon laser beam within the anterior chamber of the eye. The specific Raman signature of ganciclovir was assessed at several concentrations.

RESULTS

Spectral features unique to ganciclovir were identified and distinguished from those of ocular tissue. The amplitudes of the spectral peaks corresponding to ganciclovir exhibited a linear dependence on the local concentration of the drug in the anterior chamber of the eye.

CONCLUSION

Raman spectroscopy may offer an effective tool for the noninvasive assessment of the local concentration of ganciclovir in the ocular media. This technique offers the potential to determine both the amount and the rate of the drug release from implants designed to deliver antiviral drugs locally within the eye. The availability of such data could enable the ophthalmologist to improve treatment efficacy by avoiding premature or late surgical replacement of the implants.

New strategies for the management of AIDS-related CMV retinitis in the era of potent antiretroviral therapy

The management of AIDS-related cytomegalovirus (CMV) retinitis is evolving because of newly available anti-CMV drugs and because of the effect of potent antiretroviral therapy. New management issues are related to the improved immune function that occurs with antiretroviral drug use and to associated increases in patient survival. Patients can be categorized on the basis of their history of exposure to antiretroviral drugs and to their immune status; these factors will influence choices between treatment options. In some patients with improved immune function, specific anti-CMV therapy can be withdrawn altogether without reactivation of infection. There are currently many treatment options available for those who need specific anti-CMV treatment: ganciclovir via various routes (intravenous (IV), oral, intraocular implant); IV foscarnet; IV cidofovir; intravitreous fomivirsen; or a combination of these agents. Previous short-term therapies are being adapted to the long-term management of what has become a chronic disease. Management strategies also involve appropriate monitoring for the recurrence of disease activity and the development of complications, such as retinal detachment or immune recovery uveitis. This chapter provides an overview of new treatment strategies that will assist clinicians in choosing between treatment options.