Dexamethasone concentration in the subretinal fluid after a subconjunctival injection, a peribulbar injection, or an oral dose

Peribulbar Corticosteroids for Ocular Myasthenia Gravis

BACKGROUND

Ocular myasthenia gravis is treated predominantly by oral medications, with the potential for systemic adverse effects. Successful treatment has been achieved using peribulbar dexamethasone. We assessed the effect of peribulbar dexamethasone or triamcinolone (40-mg Triesence), a longer-acting corticosteroid, targeting the peribulbar area as opposed to directly injecting the affected extraocular muscle. This more convenient and secure approach holds the potential for straightforward integration within clinical environments.

METHODS

Retrospective chart review.

RESULTS

Five patients were identified that were treated with peribulbar corticosteroids. In 4 of the 5 cases, ophthalmoparesis was unilateral. One case had isolated ptosis, and 4 had both ptosis and ophthalmoparesis. Three of these 4 cases reported complete resolution of symptoms within weeks of a single injection. Improvement lasted between 5 to 6 months, and all patients responded to repeated injections.

CONCLUSIONS

Peribulbar corticosteroids can be effective in ocular myasthenia gravis. We suggest that longer-acting agents such as triamcinolone are preferable, to reduce injection frequency.

Glucocorticoid-Induced Ocular Hypertension and Glaucoma

Glucocorticoid (GC) therapy is indicated in many diseases, including ocular diseases. An important side-effect of GC therapy is GC-induced ocular hypertension (GIOHT), which may cause irreversible blindness known as GC-induced glaucoma (GIG). Here, we reviewed the pathological changes that contribute to GIOHT including in the trabecular meshwork and Schlemm's canal at cellular and molecular levels. We also discussed the clinical aspects of GIOHT/GIG including disease prevalence, risk factors, the type of GCs, the route of GC administration, and management strategies.

Endothelial loss following postoperative intracameral triamcinolone acetonide and subconjunctival dexamethasone injections

OBJECTIVES

To compare endothelial toxicity and efficacy of two local steroid injections (intracameral triamcinolone acetonide and subconjunctival dexamethasone) in controlling postoperative inflammation following pars plana vitrectomy (PPV) combined with phacoemulsification cataract surgery.

METHODS

This cohort included 54 patients that underwent combined surgery and received either intracameral triamcinolone acetonide injections (n = 27, IC-TA group) or subconjunctival dexamethasone (n = 27, Sc-Dex group) injections at the end of the surgery. All participants had at least 4 months or longer follow-up. A detailed ophthalmologic examination including intraocular pressure (IOP) measurement and specular microscopy was performed at every visit.

RESULTS

Endothelial cell density (ECD) reduced significantly in IC-TA group postoperatively (2418 vs. 2249, p = 0.019), while it did not change significantly in Sc-Dex group (2541 vs. 2492, p = 0.247). Postoperative ECD was also significantly lower in IC-TA group compared to Sc-Dex group (p = 0.011). Preoperative and postoperative IOP values remained unchanged both in IC-TA and Sc-Dex groups (p = 0.424 and p = 0.523, respectively). However, 4 patients in IC-TA group and 5 patients in the Sc-Dex group needed glaucoma medications. The postoperative need for glaucoma medications was similar between the groups (p = 0.347). Postoperative inflammation was well controlled in both groups and none of the patients developed fibrin membrane or synechiae postoperatively.

CONCLUSION

Both treatments were effective in controlling postoperative inflammation, but patients in IC-TA group experienced significantly higher endothelial loss. Sc-Dex injections are safer in terms of endothelial loss and preferable to control postoperative inflammation following complex intraocular surgeries.

Penetration of topically administered dexamethasone disodium phosphate and prednisolone acetate into the normal equine ocular fluids

BACKGROUND

Topical dexamethasone and prednisolone are currently the mainstay treatment for equine ophthalmic inflammatory diseases, such as equine recurrent uveitis. Comparative pharmacokinetic studies in horses are lacking and current guidelines are mainly based on empirical data and extrapolation from other species.

OBJECTIVES

To investigate the penetration and local concentrations of topically applied dexamethasone and prednisolone in normal equine ocular fluids and serum.

STUDY DESIGN

Prospective randomised experimental pharmacokinetic study.

METHODS

Twenty-one Shetland ponies without ophthalmic disease were treated bilaterally topically every 2 hours during 24 hours to obtain steady state drug concentrations. One eye was treated with 0.15 mg of dexamethasone disodium phosphate (0.1%), and the other eye was simultaneously treated with 1.5 mg of prednisolone acetate (1%). Serum samples were taken prior to the induction of general anaesthesia. Aqueous and vitreous humour samples were taken during euthanasia at time points after administration of the last dose (t = 5 min, t = 15 min, t = 30 min, t = 60 min, t = 90 min, t = 120 min, t = 180 min). Each pony was randomly assigned to one time point, and three ponies were sampled per time point. Dexamethasone and prednisolone concentrations were measured by liquid chromatography-mass spectrometry.

RESULTS

The mean dexamethasone concentration in aqueous humour was 32.4 ng/mL (standard deviation [SD] 10.9) and the mean prednisolone concentration was 321.6 ng/mL (SD 96.0). In the vitreous and in serum samples concentrations of both corticosteroids were below the limit of detection (LOD 2.5 ng/mL).

MAIN LIMITATIONS

The study group was limited to subjects without evidence of current ophthalmic disease. A limited number of time points were measured.

CONCLUSIONS

Potentially effective dexamethasone and prednisolone concentrations were measured in the anterior chamber, but vitreal concentrations were negligible. Systemic uptake was low. Therefore, treatment with only topically administered corticosteroids is deemed insufficient in horses in cases of posterior uveitis. Further studies evaluating other routes of administration are warranted.

Evaluation and Optimization of Prolonged Release Mucoadhesive Tablets of Dexamethasone for Wound Healing: In Vitro–In Vivo Profiling in Healthy Volunteers

The aim of the projected study was to design and develop a novel strategy for evaluating the mucoadhesive potential of polymeric tablets of dexamethasone (DXM) for local delivery against wounds. Therefore, formulations (Q1–Q7) were synthesized via direct compression method by varying the concentrations of polymers, i.e., ethyl cellulose (EC) and agar extract (AG). Moreover, the mucoadhesive polymeric tablets were characterized via physicochemical, in vitro, ex vivo and in vivo experiments. However, physicochemical characteristics such as FTIR showed no interaction with different polymeric combination. Surface pH of all formulations was normal to slightly alkaline. Highest hydration of up to 6.22% and swelling index was comprehended with maximum concentration of AG (50% of total tablet weight). Whereas, ex vivo and in vivo residence time and mucoadhesion were attributed to the increased concentrations of polymers. Moreover, Q7, (optimized formulation), containing 10% of EC and 40% of AG, exhibited maximum release of DXM (100%) over 8 h, along with sufficient mucoadhesive strength up to 11.73 g, following first-order kinetics having r² value of 0.9778. Hemostatic effects and epithelialization for triggering and promoting wound healing were highly pronounced in cases of Q7. Furthermore, in vivo residence time was 7.84 h followed by salivary drug concentration (4.2 µg/mL). However, mucoadhesive buccal tablets showed stability for 6 months, thus following the standardization (ICH-Iva) stability zone. In summary, DXM mucoadhesive tablets seem to be an ideal candidate for eradication of wound infections via local targeted delivery.

Corticosteroids in ophthalmology: drug delivery innovations, pharmacology, clinical applications, and future perspectives

Corticosteroids remain the mainstay of the treatment for various ocular conditions affecting the ocular surface, anterior and posterior segments of the eye due to their anti-inflammatory, anti-oedematous, and anti-neovascularization properties. Prednisolone, prednisolone acetate, dexamethasone, triamcinolone acetonide, fluocinolone acetonide, and loteprednol etabonate are amongst the most widely used ophthalmic corticosteroids. Corticosteroids differ in their activity and potency in the eye due to their inherent pharmacological and pharmaceutical differences. Different routes and regimens are available for ocular administration of corticosteroids. Conventional topical application to the eye is the route of choice when targeting diseases affecting the ocular surface and anterior segment, while periocular, intravitreal, and suprachoroidal injections can be potentially effective for posterior segment diseases. Corticosteroid-induced intraocular pressure elevation and cataract formation remain the most significant local risks following topical as well as systemic corticosteroid administration. Invasive drug administration via intracameral, subconjunctival, and intravitreal injection can enhance ocular bioavailability and minimize dose and dosing frequency of administration, yet may exacerbate ocular side effects of corticosteroids. This review provides a critical appraisal of the ophthalmic uses of corticosteroid, routes of administration, drug delivery fundamentals and novel ocular implantable steroid delivery systems, factors influencing side effects, and future perspectives for ocular corticosteroid therapy.

In vivo biocompatibility and efficacy of dexamethasone-loaded PLGA-PEG-PLGA thermogel in an alkali-burn induced corneal neovascularization disease model

Challenges of ophthalmic drug delivery arise not only from the limited solubility of hydrophobic therapeutics, but also the restricted permeability and fast clearance of drugs due to the complex anatomy and physiology of eyes. Excellent biocompatibility of a thermosensitive polymer, PLGA-PEG-PLGA (1800-1500-1800, LA:GA ratio = 3:1), as an ophthalmic delivery system was demonstrated in our previous work. In this study, delivery of dexamethasone using this thermogel via a single subconjunctival injection for prolonged treatment was evaluated with corneal neovascularization using an alkali-burn diseased model in rat. Solubility of dexamethasone in the polymeric solution was increased by 5.2-fold and the resulting drug-loaded solution formed in situ rigid gel at body temperature. Prolonged in vitro release of dexamethasone from the gel structure was noted. Dexamethasone gel formulation was demonstrated to be more effective in reducing the burn stimulus and neovascularization in the rat diseased model. The findings suggest the PLGA-PEG-PLGA in situ gelling system can be applied for ophthalmic drug delivery to achieve sustained drug release and improved efficacy.

Recent advances in the management of non-infectious posterior uveitis

PURPOSE

To review the current regimens and novel therapeutic modalities in various stages of research and development for the management of non-infectious posterior uveitis (NIPU).

METHODS

We performed a thorough review of current literature using PubMed, Google Scholar and Clinicaltrials.gov to identify the published literature about the available therapeutics and novel drugs/therapies in different stages of clinical trials.

RESULTS

The current management regimen for non-infectious posterior uveitis includes corticosteroids, immunomodulatory therapies and anti-metabolites. However, NIPU requires long-term management for efficacious remission of the disease and to prevent disease relapse. Long-term safety issues associated with steroids have led to efforts to develop novel therapeutic agents including biological response modulators and immunosuppressants. The current therapeutic agents in various stages of development include calcineurin inhibitors, biologic response modifiers and a more a comprehensive modalities like ocular gene therapy as well as novel drug delivery mechanisms for higher bioavailability to the target tissues, with minimal systemic effects.

CONCLUSION

Novel efficacious therapeutic modalities under development will help overcome the challenges associated with the traditional therapeutic agents.

Preoperative, Intraoperative and Postoperative Corticosteroid Use as an Adjunctive Treatment for Rhegmatogenous Retinal Detachment

The treatment for rhegmatogenous retinal detachment (RRD) is surgery, including pars plana vitrectomy (PPV) and scleral buckling (SB). Despite surgical advances, degeneration of the photoreceptors and post-operative complications, such as proliferative vitreoretinopathy (PVR), often occurs as the result of inflammation, preventing complete visual recovery or causing RRD recurrence. There is increasing evidence that in the presence of RRD, the activation of inflammatory processes occurs and the surgery itself induces an inflammatory response. This comprehensive review focuses on the use of different formulations of corticosteroids (CCS), as an adjunctive treatment to surgery, either PPV or SB, for RRD repair. The purpose was to review the efficacy and safety of CCS in improving functional and anatomical outcomes and in preventing postoperative complications. This review is organized according to the timing of CCS administration: preoperative, intraoperative, and postoperative. The evidence reviewed supported the role of the pre-operative use of CCS in the treatment of combined RRD and choroidal detachment (CD), reducing CD height. No solid consensus exists on intraoperative and postoperative use of CCS to treat and prevent postoperative complications. However, a large randomized clinical trial including more than 200 eyes suggested that oral prednisone after surgery decreases the rate of postoperative grade B PVR.

Recent advances in slow and sustained drug release for retina drug delivery

INTRODUCTION

Striking recent advance has occurred in the field of medical retina, greatly because intraocular drugs have been developed, enhancing their clinical efficacy while avoiding systemic side-effects. However, the burden of repeated intraocular administration makes limits the optimal efficacy of treatments, prompting the development of new drugs with prolonged half-life or of sustained drug delivery systems.

AREAS COVERED

In this review, we describe the various drugs and drug delivery systems that have reached the clinical stage and those that are in clinical development and we discuss the limitations to clinical translation.

EXPERT OPINION

Substantial fundamental work is still required to build guidelines on optimal animal models for ocular pharmacokinetics and safety studies depending on the target disease site and the on the type of therapeutic compounds. The effects of a drug administered as a bolus at high concentration in the vitreous might differ from those resulting from the sustained release of a lower concentration, and no delivery platform can be simply adapted to any drug. For the treatment of retinal diseases, development of therapeutic compounds should integrate from its early conception, the combination of an active drug with a specific drug delivery system, administered by a specific route.

Posterior segment drug delivery for the treatment of exudative age-related macular degeneration and diabetic macular oedema

Inhibitors of vascular endothelial growth factors are used to treat a myriad of retinal conditions, including exudative age-related macular degeneration (AMD), diabetic macular oedema (DME) and diabetic retinopathy. Although effective, long-term efficacy is limited by the need for frequent and invasive intravitreal injections. The quest for sustained action therapeutics that can be delivered to target tissue in the least invasive manner is an arduous endeavour that has ended in premature failure for several technologies in Phase II or III trials. Nevertheless, there have been promising preclinical studies, and more are on the horizon: port delivery systems for the treatment of exudative AMD have entered Phase III trials and a wide array of preclinical studies have demonstrated the potential for nanoparticles, such as liposomes, dendrimers and cell penetrating peptides to deliver therapeutics into the posterior segment via minimally invasive routes. In this review, we discuss the challenges posed by ocular barriers for drug penetration and present the recent advancements of the most pertinent drug delivery platforms with a focus on the treatment of exudative AMD and DME.

Biodegradable Thermosensitive PLGA-PEG-PLGA Polymer for Non-irritating and Sustained Ophthalmic Drug Delivery

Challenges of ophthalmic drug delivery arise from not only the limited solubility of hydrophobic therapeutics, but also the restricted permeability and fast clearance of drugs due to the complex anatomy and physiology of the eyes. Biodegradable thermosensitive polymer, poly(dl-lactide-co-glycolide-b-ethylene glycol-b-dl-lactide-co-glycolide) (PLGA-PEG-PLGA) is a desirable ophthalmic drug delivery system because it can be formulated into injectable solution which forms gel in situ to provide prolonged drug release. In this study, excellent biocompatibility of blank PLGA-PEG-PLGA (1800-1500-1800) thermogel was demonstrated with insignificant difference from saline noted in rat eye enucleation test, in vivo inflammation test upon topical instillation, and subconjunctival injection. After subconjunctival injection, thermogel formulations loaded with hydrophilic (rhodamine B) or hydrophobic (coumarin 6) fluorescent dyes were retained up to 4 weeks in eye tissues and significantly higher level was detected than rhodamine B solution or coumarin 6 suspension in weeks 3 and 4. Moreover, in vivo whole body imaging showed that dye-loaded (sulfo-cyanine 7 NHS ester, Cy7; or cyanine 7.5 alkyne, Cy7.5) thermogels had longer retention at the injection site and retarded release to other body parts than dye solutions. Generally, the release rate of hydrophobic dyes (coumarin 6 and Cy7.5) was much slower than that of the hydrophilic dyes (rhodamine B and Cy7) from the thermogel. In summary, the thermogel was safe for ophthalmic drug delivery and could deliver both hydrophobic and hydrophilic compounds for sustained drug release into eye tissues with single subconjunctival injection for better patient compliance and reduced risks on repeated injection.

Controlled release of corticosteroid with biodegradable nanoparticles for treating experimental autoimmune uveitis

Noninfectious uveitis is a potentially blinding ocular condition that often requires treatment with corticosteroids to prevent inflammation-related ocular complications. Severe forms of uveitis such as panuveitis that affects the whole eye often require a combination of topical and either regional or systemic corticosteroid. Regional corticosteroids are currently delivered inside the eye by intravitreal injection (e.g. Ozurdex®, an intravitreal dexamethasone implant). Intravitreal injection is associated with rare but potentially serious side effects, including endophthalmitis, retinal and vitreous hemorrhage, and retinal detachment. Subconjunctival (SCT) injection is a less invasive option that is a common route used for post-surgical drug administration and treatment of infection and severe inflammation. However, it is the water soluble form of dexamethasone, dexamethasone sodium phosphate (DSP), that has been demonstrated to achieve high intraocular penetration with subconjunctival injection. It is difficult to load highly water soluble drugs, such as DSP, and achieve sustained drug release using conventional encapsulation methods. We found that use of carboxyl-terminated poly(lactic-co-glycolic acid) (PLGA) allowed encapsulation of DSP into biodegradable nanoparticles (NP) with relatively high drug content (6% w/w) if divalent zinc ions were used as an ionic "bridge" between the PLGA and DSP. DSP-Zn-NP had an average diameter of 210 nm, narrow particle size distribution (polydispersity index ~0.1), and near neutral surface charge (-9 mV). DSP-Zn-NP administered by SCT injection provided detectable DSP levels in both the anterior chamber and vitreous chamber of the eye for at least 3 weeks. In a rat model of experimental autoimmune uveitis (EAU), inflammation was significantly reduced in both the front and back of the eye in animals that received a single SCT injection of DSP-Zn-NP as compared to animals that received either aqueous DSP solution or phosphate buffered saline (PBS). DSP-Zn-NP efficacy was evidenced by a reduced clinical disease score, decreased expression of various inflammatory cytokines, and preserved retinal structure and function. Furthermore, SCT DSP-Zn-NP significantly reduced microglia cell density in the retina, a hallmark of EAU in rats. DSP-Zn-NP hold promise as a new strategy to treat noninfectious uveitis and potentially other ocular inflammatory disorders.

Efficacy and Safety of Magnesium versus Dexmedetomidine as Additives to Local Anesthetic Mixture Using Single Injection Percutaneous Peribulbar Anesthesia in Vitreoretinal Surgeries

Background:

Peribulbar block for vitreoretinal surgery is rather associated with delayed onset of globe anesthesia, akinesia and short duration of analgesia.

Objective:

To compare the effect of addition of Magnesium sulphate vs dexmedetomidine to standard local anesthetics mixtures on the time of onset of Globe Anesthesia, Akinesia & analgesia duration.

Patients and Methods:

Ninety patients of both sexes, aged 25- 75 years, ASA I-III scheduled for vitreoretinal surgery. They were randomly allocated into 3 equal groups each received peribulbar block a mixture of Levo- bupivacaine 0.5% (3 ml) + lidocaine 2% (3 ml) +120 IU hyaluronidase + Control group (C): 0.5 ml of Normal saline. Group (M): 50 mg of Magnesium sulphate in 0.5 ml normal saline. Group (D): 50 μic of dexmedetomidine in 0.5 ml normal saline. The duration of sensory, motor block, Sedation level, Intra-ocular Pressure (IOP) and surgeon satisfaction were assessed.

Results:

The onset of globe anesthesia and akinesia was significantly shorter in M group in comparison with D and C Groups, with a significant increase in the duration of globe analgesia and akinesia in the D Group when compared to both M & C groups. Groups D and M showed a statistically significant decrease in the IOP at 5 min and 10 min when compared to the baseline measurement of the same groups & to C Group, no complications or adverse effects related to the drug or technique were recorded.

Conclusion:

Magnesium sulphate as a local anesthetic adjuvant in peribulbar block is safe and comparable to dexmedetomidine regarding the sensory and motor block duration with better cost-effectiveness and availability.

Thrombin Generation in Vitreous and Subretinal Fluid of Patients with Retinal Detachment

PURPOSE

To measure prothrombin fragments (F1+2) and thrombin-antithrombin complex (TAT) in vitreous and subretinal fluid (SRF) of rhegmatogenous retinal detachment (RRD) patients and to validate and further specify our earlier finding of increased thrombin activity in patients with proliferative vitreoretinopathy (PVR).

METHODS

F1+2 and TAT were measured in 31 vitreous and 16 SRF samples using the Enzygnost® immunoassays.

RESULTS

We found significant levels of F1+2 and TAT in the vitreous of all patients with RRD compared to patients with macular hole or macular pucker. However, there was no significant difference between patients who would develop PVR in the future, had established PVR, and patients with uncomplicated RRD both in vitreous concentrations of F1+2 (Kruskal-Wallis p = 0.963) and TAT (p = 0.516).

CONCLUSION

The analysis of F1+2 and TAT confirmed significant thrombin generation in both vitreous and SRF of patients with RRD. An imbalance between the thrombin regulation mechanisms TAT and α2-macroglobulin possibly explains the difference from our previous findings.

Ocular Drug Distribution and Safety of a Noninvasive Ocular Drug Delivery System of Dexamethasone Sodium Phosphate in Rabbit

PURPOSE

To determine the ocular toxicity, systemic exposure, and amounts of dexamethasone sodium phosphate (DSP) in ocular tissues after administration of DSP with the Visulex system (DSP-Visulex).

METHODS

DSP-Visulex was applied onto healthy rabbit eyes. DSP concentrations (4%, 8%, 15%, and 25%) and treatment durations (5, 10, and 20 min) were evaluated for the amounts of DSP in the ocular tissues and in plasma after single administrations of DSP-Visulex. The drug in eye tissues and plasma was analyzed by high-performance liquid chromatography-UV/VIS and by liquid chromatography-mass spectrometry, respectively. The safety and tolerability were ascertained based on clinical observations and histopathological examinations from repeat weekly DSP-Visulex treatments (4%, 8%, 15%, and 25% for 20 min) for 12 weeks.

RESULTS

Significant amounts of DSP (ie, higher than 1 μg/g) were found in the anterior chamber, retina-choroid, cornea, vitreous, conjunctiva, and sclera after single applications of DSP-Visulex. The DSP concentrations in the ocular tissues and in plasma increased with increased DSP concentrations in the Visulex applicator and with increased application times. Systemic DSP was rapidly detected. The plasma half-life was 2-3 h. C_max was 148 and 1,844 ng/mL, and the area under the plasma drug concentration versus time curve (AUC) was 418 and 3,779 ng · h/mL for the low dose (4% DSP-Visulex for 5 min) and the high dose (15% DSP-Visulex for 20 min), respectively. Ocular findings over 12 weeks were mostly conjunctival injection and eye discharge. These were transient and mild. Histopathological examinations indicated the eyes to be normal.

CONCLUSIONS

DSP can be administered safely and effectively into the rabbit eye with the Visulex system. Treatment duration and DSP concentration are important factors in achieving therapeutic levels. Repeat applications of DSP-Visulex are safe and well tolerated for weekly administrations over 4-12 weeks. DSP-Visulex has clinical potential for the noninvasive treatment of ocular diseases.

Intravitreal Triamcinolone Acetonide in Refractory Pseudophakic Cystoid Macular Edema: Functional and Anatomic Results

PURPOSE

To evaluate safety and efficacy of intravitreal triamcinolone acetonide (TAAC) injections in the treatment of refractory pseudophakic cystoid macular edema (CME).

METHODS

Seven eyes of six patients (age range: 50-74) with pseudophakic CME resistant to standard treatment received intravitreal injections of 4 mg of TAAC with all vehicle. Mean preinjection duration of CME was 18.3 months. A mean of 2.1+/-1.2 (range 1 to 4) treatments were performed in four eyes (57.1 %) when visual acuity deteriorated towards baseline levels. Visual acuity assessment, optical coherence tomography (OCT), and fluorescein angiography (FFA) were performed pre- and postoperatively to evaluate results of TAAC injections. Intraocular pressure (IOP) and complications related to treatment were assessed.

RESULTS

After 11.1+/-3.9 months, mean best-corrected visual acuity (BCVA) increased (p =0.019) from 20/132 to a best value of 20/38. Mean macular thickness decreased from 517.29+/-146.98 mm to a best value of 263.71+/-83.13 mm (p=0.0018). Area of fluorescein leakage decreased (p<0.0001) from 11.84+/-0.93 mm2 at baseline to a minimal value of 3.86+/-0.98 mm2. The anatomic and functional improvement appeared after 1 month from the intravitreal injection and persisted through at least 3 months of follow-up. At the end of follow-up BCVA, macular thickness, and area of fluorescein leakage did not differ from baseline. Four eyes (57.1 %) developed IOP values higher than 21 mmHg, controlled by topical treatment. Two patients developed an endophthalmitis-like reaction.

CONCLUSIONS

Intravitreal TAAC was relatively safe and effective in resistant cases of pseudophakic CME with a temporary beneficial effect on visual acuity and macular edema.

Clinical Outcomes of Adjunctive Sustained-Release Intravitreal Dexamethasone Implants in Tuberculosis-Associated Multifocal Serpigenoid Choroiditis

PURPOSE

To analyze the safety and efficacy of sustained-release intravitreal dexamethasone implant (Ozurdex) in management of TB-associated multifocal serpiginoid choroiditis (MSC).

METHODS

Retrospective review of TB-associated MSC patients, treated with anti-TB therapy (ATT) and adjunctive intravitreal Ozurdex.

RESULTS

Nine eyes of six patients were included. Four patients required Ozurdex implant for progressive or new lesions following ATT and two for additional systemic contraindications to corticosteroids - hyperglycemia and uncontrolled hypertension, respectively. The mean time to resolution was 9.17 ± 7.71 weeks. The mean follow-up post-injection was 13.11 ± 6.05 months (median 12 months [range 6-24.5 months]). Only one of nine eyes developed recurrent MSC lesions and this was attributed to possible autoimmune etiology. Two eyes (22.2%) developed steroid-induced glaucoma - one required implant removal.

CONCLUSIONS

Sustained-release intravitreal dexamethasone is a safe and efficacious adjunctive anti-inflammatory therapy for TB-associated MSC patients with contraindication for systemic corticosteroids or requiring supplemental anti-inflammatory 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.

Ocular Pharmacokinetics

Although the fundamental concepts of pharmacokinetics remain the same, ocular pharmacokinetics has its own challenges due to the uniqueness of barrier properties posed by various ocular tissues and its growing complexity with different routes of ocular administration. A thorough understanding of the barrier nature will aid in tailoring a drug or its carrier's physicochemical properties to its advantage. In order to deliver the right payload of a drug at the target site, various approaches can be taken to leverage the pharmacokinetics that includes molecular design based on desirable physicochemical properties, formulation approaches, and alternative routes of administration. In this chapter, a brief overview of the barrier properties with respect to various routes of administration is presented along with the physicochemical properties that influence the pharmacokinetics of ocular drugs. Recent advances in ocular pharmacokinetics are discussed in addition to new perspectives in interpreting existing data.

Vitreous and subretinal fluid concentrations of orally administered dabigatran in patients with rhegmatogenous retinal detachment

PURPOSE

One of the factors that was shown to contribute to the development of proliferative vitreoretinopathy (PVR) is the coagulation factor thrombin. Therefore, a specific oral thrombin inhibitor such as dabigatran might be a possible therapeutic option. An oral drug has the advantage of patient-friendly prolonged administration in contrast to drugs that can only be applied during vitrectomy, on condition that the drug reaches the target site. We tested whether dabigatran reaches the vitreous and subretinal fluid (SRF) after a single oral dose of dabigatran.

METHODS

Twenty-eight patients with a retinal detachment received a single dose of 220 mg dabigatran etexilate 2-8 hr prior to surgery. During surgery, we took a blood sample and a vitreous or subretinal fluid sample. The concentration of dabigatran was measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

The dabigatran concentration between 2 and 9 hr after administration was higher in SRF than in vitreous (max 8.5 and 3.8 ng/ml). Corresponding plasma concentrations ranged from 15 to 225 ng/ml. There was a significant relationship between SRF levels and plasma levels (r_s  = 0.68, p = 0.014); the levels in vitreous fluid showed no such relationship (r_s  = 0.20, p = 0.48). In addition, we measured the vitreous concentration of a non-study patient using 150 mg dabigatran twice daily. The concentration was approximately 10 times higher than after a single dosage (25.8 ng/ml).

CONCLUSION

We demonstrate that oral intake of dabigatran, a candidate drug to modulate PVR, results in potentially relevant intraocular concentrations. We suggest that repeated dosing may lead to higher concentrations, but this should be further explored.

Effect of addition of magnesium to local anesthetics for peribulbar block: A prospective randomized double-blind study

Background:

Magnesium sulphate has been used along with local anesthetics in different regional blocks and found to be effective in decreasing the time of onset of the block and increasing the duration of the block.

Objective:

To evaluate the effect of addition of magnesium sulfate to standard local anesthetics mixture on the time for onset of the globe and lid akinesia for peribulbar block in ophthalmic surgeries.

Materials and Methods:

Sixty patients with American Society of Anesthesiologists status I to III undergoing ophthalmic surgery under peribulbar block were included in this study. Patients were randomized into two groups. Both the groups received 4.5 ml of 2% lidocaine, 4.5 ml of 0.5% bupivacaine with150 IU hyaluronidase. Group NS received normal saline 1 ml in the peribulbar block and Group MS, magnesium sulfate 50 mg in 1 ml normal saline. The onset of akinesia, satisfactory block and complications were observed by an independent observer.

Results:

Demographic data was statistically similar. In the Group NS at 3, 5, 10 and 15 min after the block, complete akinesia was seen in 0, 2, 11 and 28 patients respectively. In the Group MS, at 3, 5, 10 and 15 min after the block, complete akinesia was seen in 13, 23, 27 and 28 patients respectively. Patients received magnesium sulfate showed the statistically significant rapid onset of lid and globe akinesia than the control group till 10 min (P < 0.000). None of the patients needed a supplementary block and had complications during the surgery.

Conclusion:

Addition of 50 mg of magnesium sulfate to the lidocaine-bupivacaine mixture for peribulbar block decreases the onset of akinesia without any obvious side effect.

The Effects of Ozurdex® (Dexamethasone Intravitreal Implant) on Experimental Proliferative Vitreoretinopathy

Purpose: To investigate a new sustained-release formulation of dexamethasone (Ozurdex®) for inhibiting proliferative vitreoretinopathy (PVR) and its effect on the expression of retinal glial reaction and inflammation in experimental PVR eyes. Methods: We used 30 pigmented rabbits for this study. One week after gas compression, the eyes were injected with 5 × 104 retinal pigment epithelial cells into the vitreous cavity to induce PVR. Concurrently, one eye also received an intravitreal injection of Ozurdex; the other eye was used as a control. PVR was graded by indirect ophthalmoscopy on days 1, 3, 7, 14, 21, and 28. The expression of the retinal glial reaction and inflammation in experimental PVR eyes were evaluated by Western blot analysis. Results: PVR severity increased gradually and peaked after 14 days, and no differences in PVR severity between the study and control groups were observed at any time point. The expression of glial fibrillary acid protein (GFAP) increased on days 7 and 14 in both the PVR control and study groups. While the use of Ozurdex in the study group showed less GFAP expression, this difference was not significant. The expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 significantly increased on days 7 and 14 in PVR control eyes. There was a significant difference in TNF-α between PVR control eyes and Ozurdex-treated eyes on days 7 (p < 0.001) and 14 (p = 0.019). Ozurdex in the study group showed lower IL-6 expression; however, this difference was not significant on days 7 (p = 0.063) and 14 (p = 0.052). Conclusions: The intravitreal injection of Ozurdex suppressed the expression of inflammatory markers; however, it did not mitigate the severity of experimental PVR in this animal model.

Optimization of dexamethasone mixed nanomicellar formulation

The purpose of this study was to develop a clear aqueous mixed nanomicellar formulation (MNF) of dexamethasone utilizing both D-α-tocopherol polyethylene glycol-1000 succinate (Vit E TPGS) and octoxynol-40 (Oc-40). In this study, Vit E TPGS and Oc-40 are independent variables. Formulations were prepared following solvent evaporation method. A three level full-factorial design was applied to optimize the formulation based on entrapment efficiency, size, and polydispersity index (PDI). A specific blend of Vit E TPGS and Oc-40 at a particular wt% ratio (4.5:2.0) produced excellent drug entrapment, loading, small mixed nanomicellar size and narrow PDI. Solubility of DEX in MNF is improved by ~6.3-fold relative to normal aqueous solubility. Critical micellar concentration (CMC) for blend of polymers (4.5:2.0) was found to be lower (0.012 wt%) than the individual polymers (Vit E TPGS (0.025 wt%) and Oc-40 (0.107 wt%)). No significant effect on mixed nanomicellar size and PDI with one-factor or multi-factor interactions was observed. Qualitative (1)H NMR studies confirmed absence of free drug in the outer aqueous MNF medium. MNF appeared to be highly stable. Cytotoxicity studies on rabbit primary corneal epithelial cells did not indicate any toxicity suggesting MNF of dexamethasone is safe and suitable for human topical ocular drops after further in vivo evaluations.

[Safety and efficacy of subconjunctival triamcinolone injections in the management of uveitic macular edema: retrospective study of thirty-one cases]

Triamcinolone acetonide (Kenacort) is a corticosteroid that can be administrated by subconjunctival injection, with an extended release for up to three months. Our retrospective study aims to analyze safety and efficacy of subconjunctival triamcinolone injections in the treatment of uveitic macular edema. We included 31 eyes of 30 patients, who had one or several injections. We studied the progression of visual acuity, central macular thickness by optical coherence tomography (OCT), intraocular pressure, and presence or absence of cataract, on the day of injection (T0), and at 1, 3, 6 and 12 months after injection. Twenty-one patients had only one injection; 10 patients had 2. The 12-month follow-up showed an improvement in visual acuity with an initial mean of 0.36 ± 0.27 logMAR to 0.23 ± 0.33 logMAR at 3 months of follow-up (P<0.0004), and to 0.24 ± 0.21 logMAR at 12 months (P=0.0371), for a two-line improvement. A decrease in mean central macular thickness was measured by OCT, from a mean of 444 ± 112 μm (0.24 ± 0.11 logSD-OCT) at T0 to 355 ± 103 μm (0.14 $ ± 0.10 logSD-OCT) at 3 months (P=0.0002). We did not find a significant increase in intraocular pressure, and we diagnosed one cataract during follow-up but this occurred in the uninjected eye as well. Subconjunctival injection of triamcinolone acetonide is a safe and effective treatment of macular edema related to uveitis. Initial clinical monitoring is necessary to detect iatrogenic events.

Pharmacokinetics and efficacy of Bioerodible Dexamethasone implant in Concanavalin A-induced uveitic cataract rabbit model

PURPOSE

To advance therapy for the treatment of concurrent uveitis and post-cataract surgical inflammation; we evaluated pharmacokinetics and pharmacodynamics of Bioerodible Dexamethasone Implant (BDI) containing 0.3 mg of dexamethasone (DXM) in Concanavalin A (Con A) induced uveitis followed by phacoemulsification in New Zealand White (NZW) rabbits.

METHODS

The BDI was implanted in the inferior fornix of the capsular bag after intravitreal injection of Con A and ensuing phacoemulsification in NZW rabbits; standard-of-care topical 0.1% dexamethasone drops served as control. DXM was quantified by liquid chromatography-tandem mass spectrometry and pharmacokinetics of DXM in disease vs. healthy eyes was compared. All eyes were assessed clinically using slit lamp biomicroscopy and Draize scoring scale. Retinal thickness and histological analyses were performed to evaluate retinal edema, inflammation and implant biocompatibility respectively.

RESULTS

In Con A-induced inflammatory uveitic cataract model the BDI controlled anterior and posterior segment inflammation as well as retinal thickening more effectively than topical drops. The exposure (AUC0-t) of DXM with BDI is superior in all ocular tissues, while topical drops did not achieve therapeutic posterior segment levels and did not control inflammation nor prevent retinal edema and architectural disruption.

CONCLUSIONS

Our results demonstrate the superiority of the BDI in suppressing Con A-induced inflammation and retinal edema in NZW rabbits and highlight the need for sustained bidirectional delivery of potent anti-inflammatory agents for 5 to 6 weeks to optimize clinical outcomes.

Pharmacokinetics and efficacy of the spleen tyrosine kinase inhibitor r406 after ocular delivery for retinoblastoma

PURPOSE

Retinoblastoma is a childhood cancer of the retina. Clinical trials have shown that local delivery of broad spectrum chemotherapeutic agents is efficacious. Recent studies characterizing the genomic and epigenomic landscape of retinoblastoma identified spleen tyrosine kinase (SYK) as a promising candidate for targeted therapy. The purpose of this study was to conduct preclinical testing of the SYK antagonist R406 to evaluate it as a candidate for retinoblastoma treatment.

METHODS

The efficacy of the SYK antagonist R406 delivered locally in a human orthotopic xenograft mouse model of retinoblastoma was tested. Intraocular exposure of R406 was determined for various routes and formulations.

RESULTS

There was no evidence of efficacy for subconjunctival. R406. Maximal vitreal concentration was 10-fold lower than the minimal concentration required to kill retinoblastoma cells in vitro. Dosage of R406 subconjunctivally from emulsion or suspension formulations, direct intravitreal injection of the soluble prodrug of R406 (R788), and repeated topical administration of R406 all increased vitreal exposure, but failed to reach the exposure required for retinoblastoma cell death in culture.

CONCLUSION

Taken together, these data suggest that R406 is not a viable clinical candidate for the treatment of retinoblastoma. This study highlights the importance of pharmacokinetic testing of molecular targeted retinoblastoma therapeutics.

Pharmacologic and clinical profile of dexamethasone intravitreal implant

The challenge in the treatment of chronic retinal diseases is to deliver effective therapy to the target tissues in the back of the eye while limiting drug exposure in nontarget tissues. Intravitreal placement provides the most targeted drug delivery, but repeated penetration of the globe to deliver intravitreal therapy can pose safety risks. A more effective strategy for the treatment of chronic retinal diseases would be to combine intravitreal placement with sustained drug delivery. The dexamethasone intravitreal (DEX) implant is a biodegradable sustained-release intravitreal drug delivery system that is approved for the treatment of macular edema following branch or central retinal vein occlusion and for noninfectious uveitis affecting the posterior segment of the eye. A single DEX implant has been shown to provide clinical benefits for up to 6 months in eyes with retinal vein occlusion or intermediate or posterior uveitis.

Nanomedicines for back of the eye drug delivery, gene delivery, and imaging

Treatment and management of diseases of the posterior segment of the eye such as diabetic retinopathy, retinoblastoma, retinitis pigmentosa, and choroidal neovascularization is a challenging task due to the anatomy and physiology of ocular barriers. For instance, traditional routes of drug delivery for therapeutic treatment are hindered by poor intraocular penetration and/or rapid ocular elimination. One possible approach to improve ocular therapy is to employ nanotechnology. Nanomedicines, products of nanotechnology, having at least one dimension in the nanoscale include nanoparticles, micelles, nanotubes, and dendrimers, with and without targeting ligands. Nanomedicines are making a significant impact in the fields of ocular drug delivery, gene delivery, and imaging, the focus of this review. Key applications of nanotechnology discussed in this review include a) bioadhesive nanomedicines; b) functionalized nanomedicines that enhance target recognition and/or cell entry; c) nanomedicines capable of controlled release of the payload; d) nanomedicines capable of enhancing gene transfection and duration of transfection; f) nanomedicines responsive to stimuli including light, heat, ultrasound, electrical signals, pH, and oxidative stress; g) diversely sized and colored nanoparticles for imaging, and h) nanowires for retinal prostheses. Additionally, nanofabricated delivery systems including implants, films, microparticles, and nanoparticles are described. Although the above nanomedicines may be administered by various routes including topical, intravitreal, intravenous, transscleral, suprachoroidal, and subretinal routes, each nanomedicine should be tailored for the disease, drug, and site of administration. In addition to the nature of materials used in nanomedicine design, depending on the site of nanomedicine administration, clearance and toxicity are expected to differ.

The dexamethasone drug delivery system: indications and evidence

INTRODUCTION

The Ozurdex(®) (Allergan Inc., Irvine, CA, USA) dexamethasone drug delivery system (DDS) was recently developed as a biodegradable intravitreal implant to provide sustained delivery of 700 μg of preservativefree dexamethasone to the retina and vitreous, and is approved by the United States Food and Drug Administration (FDA) for the treatment of macular edema associated with retinal vein occlusion, as well as for noninfectious posterior uveitis. This review summarizes the rationale behind the development of the dexamethasone DDS, evidence for its use in various clinical scenarios, and compares its efficacy to other available treatment options.

METHODS

Published data regarding the dexamethasone DDS as well as unpublished data that has been presented at national meetings were reviewed.

RESULTS

The dexamethasone DDS has evidence for efficacy in multiple clinical situations, including macular edema associated with retinal vein occlusion (RVO), macular edema associated with uveitis or Irvine-Gass syndrome, diabetic macular edema in vitrectomized eyes, persistent macular edema, noninfectious vitritis, and as adjunctive therapy for age-related macular degeneration. Safety concerns include cataract formation and intraocular pressure elevation that is most often temporary and amenable to medical management.

CONCLUSIONS

The dexamethasone DDS is one of the most recent additions to the armamentarium against macular edema, and is intriguing for its potency, dose consistency, potential for extended duration of action, and favorable safety profile. Early evidence shows clinical utility for several conditions, the most well established being for macular edema associated with RVO. Future studies and, in particular, head-to-head comparisons with other treatment modalities will elucidate the precise role for the dexamethasone DDS in clinical practice.

Penetration of topically applied diclofenac and ketorolac into the aqueous humour and subretinal fluid: randomized clinical trial

OBJECTIVE

To determine the level of intraocular penetration of diclofenac sodium and ketorolac tromethamine into the aqueous humour and subretinal fluid.

DESIGN

Prospective randomized clinical trial.

PARTICIPANTS

Twenty eyes scheduled for retinal detachment surgery and 17 eyes scheduled for cataract surgery.

METHODS

Patients with retinal detachment were randomly assigned to receive either topical ketorolac (n = 11) or topical diclofenac (n = 9). Subretinal fluid samples were collected 30-60 minutes after the administration of the last dose. In addition, 17 patients with cataract were randomly assigned to receive topical ketorolac (n = 9) or topical diclofenac (n = 8). The aqueous humour samples were collected 30 minutes after the administration of the last dose. Drug concentrations were determined by high-performance liquid chromatography fluorescence.

RESULTS

The mean diclofenac concentration in the subretinal fluid was 42.31 (SD 24.89) ng/µL. Ketorolac was undetectable in the subretinal fluid in all patients who received it because ketorolac tromethamine levels were under the limit of detection. In the aqueous humour, mean diclofenac concentration was 4.98 (SD 4.56) ng/µL, and mean ketorolac concentration was 20.17 (SD 12.21) ng/µL. Topical administration of diclofenac sodium yielded 8.4 times greater drug concentration in the subretinal fluid than in the aqueous humour. Aqueous humour concentrations of ketorolac were higher than those of diclofenac (p = 0.019).

CONCLUSIONS

The concentration in the subretinal fluid of topically applied diclofenac was higher than that of ketorolac; and topical ketorolac penetrated into the aqueous humour better than diclofenac did. This suggests that diclofenac can be used more effectively in events related to posterior segment and ketorolac in anterior segment events.

Novel nanoparticulate gel formulations of steroids for the treatment of macular edema

PURPOSE

This article describes the development and characterization of PLGA nanoparticles of dexamethasone (DEX), hydrocortisone acetate (HA), and prednisolone acetate (PA) suspended in thermosensitive gels indicated for the treatment of macular edema (ME).

METHODS

Nanoparticles were prepared by oil-in-water (O/W) emulsion and dialysis methods using PLGA 50:50 and PLGA 65:35. These particles were characterized for entrapment efficiency, size distribution, surface morphology, crystallinity, and in vitro release. Further, ex vivo permeation studies of DEX in suspension and nanoparticulate formulations were carried out across the rabbit sclera.

RESULTS

Entrapment efficiencies of DEX, HA, and PA were found to be lower with the dialysis method. O/W emulsion/solvent evaporation technique resulted in higher entrapment efficiencies, that is, 77.3%, 91.3%, 92.3% for DEX, HA, and PA, respectively. Release from nanoparticles suspended in thermosensitive gels followed zero-order kinetics with no apparent burst effect. Ex vivo permeability studies further confirmed sustained release of DEX from nanoparticles suspended in thermosensitive gels.

CONCLUSIONS

These novel nanoparticulate systems containing particles suspended in thermosensitive gels may provide sustained retina/choroid delivery of steroids following episcleral administration.

The effect of a preoperative subconjuntival injection of dexamethasone on blood-retinal barrier breakdown following scleral buckling retinal detachment surgery: a prospective randomized placebo-controlled double blind clinical trial

Background

Blood–retinal barrier breakdown secondary to retinal detachment and retinal detachment repair is a factor in the pathogenesis of proliferative vitreoretinopathy (PVR). We wished to investigate whether an estimated 700 to 1000 ng/ml subretinal dexamethasone concentration at the time of surgery would decrease the blood–retinal barrier breakdown postoperatively.

Methods

Prospective, placebo-controlled, double blind clinical trial. In 34 patients with rhegmatogenous retinal detachment scheduled for conventional scleral buckling retinal detachment surgery, a subconjunctival injection of 0.5 ml dexamethasone diphosphate (10 mg) or 0.5 ml placebo was given 5–6 hours before surgery. Differences in laser flare photometry (KOWA) measurements taken 1, 3 and 6 weeks after randomisation between dexamethasone and placebo were analysed using mixed model ANOVA, while correcting for the preoperative flare measurement.

Results

Six patients did not complete the study, one because of recurrent detachment within 1 week, and five because they missed their postoperative laser flare visits. The use of dexamethasone resulted in a statistically significant decrease in laser flare measurements at the 1-week postoperative visit.

Conclusion

The use of a preoperative subconjunctival injection of dexamethasone decreased 1-week postoperative blood–retina barrier breakdown in patients undergoing conventional scleral buckling retinal detachment surgery. This steroid priming could be useful as a part of a peri-operative regime that would aim at decreasing the incidence of PVR.

Systemic absorption of triamcinolone acetonide after posterior sub-Tenon injection

PURPOSE

To study systemic absorption of triamcinolone acetonide (TA) after posterior sub-Tenon injection.

DESIGN

Prospective, interventional case series.

METHODS

The study was conducted in a tertiary care teaching hospital on 35 eyes in which posterior sub-Tenon injection of 40 mg TA was administered after conventional extracapsular cataract extraction. Patients who had received any systemic steroid over 6 weeks preceding the period of study or had inflammatory ocular conditions were excluded. Serum TA levels were estimated by high-performance liquid chromatography at 1, 2, 3, 24, and 48 hours and 1, 2, and 6 weeks after injection.

RESULTS

Significant levels of the drug were detected in 45.71% of samples (mean serum levels, 6.94 +/- 8.98 ng/ml; P < .001) at 1 hour after sub-Tenon injection, in 85.71% of samples (mean serum levels, 21.83 +/- 12.92 ng/ml; P < .001) at 2 hours after injection, in 100% of samples (mean serum levels, 47.14 +/- 12.20 ng/ml; P < .001) at 3 hours after injection, in 100% of samples (mean serum levels, 35.49 +/- 13.79 ng/ml; P < .001) at 24 hours after injection, in 62.86% of samples (mean serum levels, 10.46 +/- 10.69 ng/ml; P < .001) at 48 hours after injection, and in 28.57% of samples (mean serum levels, 3.74 +/- 6.45 ng/ml; P = .002) at 1 week after injection. The drug was not detected in any of the samples obtained 2 weeks and 6 weeks later.

CONCLUSIONS

Posterior sub-Tenon injection of 40 mg TA adds statistically significant quantities to physiologic concentration of corticosteroids in peripheral blood. This may be detrimental for patients having certain metabolic diseases like diabetes and preferably should be avoided or administered with caution.

Pharmacokinetic study of dexamethasone disodium phosphate using intravitreal, subconjunctival, and intravenous delivery routes in rabbits

Dexamethasone is a corticosteroid with proven efficacy for treating both anterior- and posterior-segment ocular diseases. Delivery of drugs to the back of the eye has always been a challenge, with dexamethasone being no exception. There are multiple delivery routes to the retina, with each exhibiting different pharmacokinetics, depending on the drug molecule and specific route of administration. In this study, we used intravenous (IV), subconjunctival (SC), and intravitreal (IVT) injections in rabbits to determine the pharmacokinetics of dexamethasone phosphate and its metabolic product, dexamethasone, at low (25 microg/kg) and high (250 microg/kg) doses. Plasma samples were collected from each group of animals at different time points up to 24 h after the injection. Using a liquid chromatographic mass spectrometric method with a limit of detection of 0.5 ng/mL, the plasma concentration for dexamethasone and its prodrug compound were quantified. IV delivery showed the fastest plasma elimination, followed by SC delivery. IVT delivery exhibited a depot effect, with very low plasma levels throughout the 24-h time course. At 24 h postinjection, only the high-dose IVT and low- and high-dose SC dexamethasone injections were still detectable in the plasma.

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.

The effect of recombinant human hyaluronidase on dexamethasone penetration into the posterior segment of the eye after sub-Tenon's injection

PURPOSE

The aim of this study was to investigate the extent if recombinant human hyaluronidase (rhuPH20) can enhance trans-scleral penetration of sub-Tenon's dexamethasone (DM) into the posterior segment of the eye.

METHODS

rhuPH20 was purified from conditioned media through a series of ion exchange, hydrophobic interaction, aminophenylboronate, and hydroxyapatite chromatography to greater than 90% purity based upon specific activity. Only the right eye of each rabbit was injected. The first group (n = 16) received an injection of DM and rhuPH20, whereas the second group (n = 16) received DM only. The eyes were enucleated 1, 2, 3, and 6 h after the injection, and the choroid, retina, vitreous, aqueous, and serum were harvested. DM concentration was assessed by mass spectrometry. Histology (n = 2) and immunohistochemistry (n = 2) was performed to detect toxicity and the presence of the rHuPH20, respectively.

RESULTS

We observed no histopathologic damage to ocular tissues after sub-Tenon's injection. This enzyme significantly increased DM level in the choroid and the retina 3 h after administration. The rise in levels was transient returning to normal levels by 6 h.

CONCLUSIONS

Sub-Tenon's coinjection of rHuPH20 with DM resulted in a general increase in DM levels in ocular tissues and the serum, with significant increase in the choroid and the retina, 3 h after administration.

Hyperglycemia after repeated periocular dexamethasone injections in patients with diabetes

PURPOSE

To assess the hyperglycemic effect of 3 consecutive daily periocular steroid injections in patients with diabetes.

DESIGN

Retrospective observational study in a national eye center.

PARTICIPANTS

Twenty-five hospitalized patients with type 2 diabetes who received a subconjunctival (n = 11) or a peribulbar injection (n = 14) with 4 mg dexamethasone disodium phosphate once a day for 3 consecutive days for ocular conditions.

METHODS

Baseline patient characteristics were recorded as well as serial blood glucose measurements and hypoglycemic interventions, both performed according to a written protocol.

MAIN OUTCOME MEASURES

Serial blood glucose measurements and hypoglycemic interventions.

RESULTS

Each ocular injection with dexamethasone was followed around 6 hours later by an increase of blood glucose up to a median doubling from baseline (+100% increase) followed by falls until the next injection, toward a median 13% increase from baseline before the next ocular injection. Older age (P<0.05), duration of diabetes (P = 0.01), and microangiopathy or macroangiopathy (P = 0.01) were associated with higher blood glucose rises. Using a 14-mmol/l threshold for intervention, the probability of requiring additional hypoglycemic treatment during ocular steroid therapy in patients with HbA1c >7.5% and up to 7.5% was 100% and 60%, respectively.

CONCLUSIONS

Periocular injections with dexamethasone in patients with type 2 diabetes induce a marked hyperglycemic effect, similar to that observed during intravenous pulse methylprednisolone.

Ocular drug delivery

Drug delivery to the eye is hampered by anatomical factors, including the corneal epithelium, the blood-aqueous barrier and the blood-retinal barrier. This review aims to outline the major routes of ocular drug delivery, including systemic, topical, periocular and intravitreal. The pharmacokinetics, the disadvantages and the clinical relevance of these drug delivery routes have been emphasised. Recent advances in surgical techniques, therapeutic approaches and material sciences have produced exciting new therapies for ocular diseases. The role of ophthalmic drug formulation in targeting the desired ocular tissue and enhancing drug delivery by the chosen route whilst minimising side effects is also discussed.