Intravitreal delivery of ganciclovir in rabbits by transscleral iontophoresis

Application of iontophoresis in ophthalmic practice: an innovative strategy to deliver drugs into the eye

Delivery of drugs to special locations of ocular lesions, while minimizing systemic and local toxic effects, is recognized as a critical challenge in the ophthalmic practice. The special anatomy and physiology barriers within the eyeball entail effective drug delivery systems. Emerging attempts in drug delivery has led to developments in ocular iontophoresis, which acts as a noninvasive technology to enhance drug penetration using a small electric current. This technique offers greater flexibility to deliver desired drug dose in a controlled and tolerable manner. In previous studies, this technique has been testified to deliver antibiotics, corticoid, proteins and other gene drugs into the eye with the potency of treating or alleviating diverse ophthalmological diseases including uveitis, cataract, retinoblastoma, herpes simplex and cytomegalovirus retinitis (CMVR), etc. In this review, we will introduce the recent developments in iontophoresis device. We also summarize the latest progress in coulomb controlled iontophoresis (CCI), hydrogel ionic circuit (HIC) and EyeGate II delivery system (EGDS), as well as overview the potential toxicity of iontophoresis. We will discuss these factors that affect the efficacy of iontophoresis experiments, and focus on the latest progress in its clinical application in the treatment of eye diseases.

Therapeutic Systems and Technologies: State-of-the-Art Applications, Opportunities, and Challenges

In this review, we present current state-of-the-art developments and challenges in the areas of thermal therapy, ultrasound tomography, image-guided therapies, ocular drug delivery, and robotic devices in neurorehabilitation. Additionally, intellectual property and regulatory aspects pertaining to therapeutic systems and technologies are addressed.

Ultrasound-enhanced ocular delivery of dexamethasone sodium phosphate: an in vivo study

BACKGROUND

The eye's unique anatomy and its physiological and anatomical barriers can limit effective drug delivery into the eye.

METHODS

An in vivo study was designed to determine the effectiveness and safety of ultrasound application in enhancing drug delivery in a rabbit model. Permeability of a steroid ophthalmic drug, dexamethasone sodium phosphate, was investigated in ultrasound- and sham-treated cases. For this study, an eye cup filled with dexamethasone sodium phosphate was placed on the cornea. Ultrasound was applied at intensity of 0.8 W/cm(2) and frequency of 400 or 600 kHz for 5 min. The drug concentration in aqueous humor samples, collected 90 min after the treatment, was determined using chromatography methods. Light microscopy observations were done to determine the structural changes in the cornea as a result of ultrasound application.

RESULTS

An increase in drug concentration in aqueous humor samples of 2.8 times (p < 0.05) with ultrasound application at 400 kHz and 2.4 times (p < 0.01) with ultrasound application at 600 kHz was observed as compared to sham-treated samples. Histological analysis showed that the structural changes in the corneas exposed to ultrasound predominantly consisted of minor epithelial disorganization.

CONCLUSIONS

Ultrasound application enhanced the delivery of an anti-inflammatory ocular drug, dexamethasone sodium phosphate, through the cornea in vivo. Ultrasound-enhanced ocular drug delivery appears to be a promising area of research with a potential future application in a clinical setting.

New techniques for drug delivery to the posterior eye segment

Ocular drug delivery has become an increasingly important field of research especially when treating posterior segment diseases of the eye, such as age-related macular degeneration, diabetic retinopathy, posterior uveitis and retinitis. These diseases are the leading causes of vision loss in developed countries which require repeated long-term administration of therapeutic agents. New drugs for the medication of the posterior ocular segment have emerged, but most drugs are delivered by repeated intravitreal injections associated with ocular complications. Advances in ocular drug delivery system research are expected to provide new tools for the treatment of the posterior segment diseases, providing improved drug penetration, prolonged action, higher efficacy, improved safety and less invasive administration, resulting in higher patient compliance. This review provides an insight into the recent progress and trends in ocular drug delivery systems for treating posterior eye segment diseases, with an emphasis on transscleral iontophoresis.

Recent perspectives in ocular drug delivery

Anatomy and physiology of the eye makes it a highly protected organ. Designing an effective therapy for ocular diseases, especially for the posterior segment, has been considered as a formidable task. Limitations of topical and intravitreal route of administration have challenged scientists to find alternative mode of administration like periocular routes. Transporter targeted drug delivery has generated a great deal of interest in the field because of its potential to overcome many barriers associated with current therapy. Application of nanotechnology has been very promising in the treatment of a gamut of diseases. In this review, we have briefly discussed several ocular drug delivery systems such as microemulsions, nanosuspensions, nanoparticles, liposomes, niosomes, dendrimers, implants, and hydrogels. Potential for ocular gene therapy has also been described in this article. In near future, a great deal of attention will be paid to develop non-invasive sustained drug release for both anterior and posterior segment eye disorders. A better understanding of nature of ocular diseases, barriers and factors affecting in vivo performance, would greatly drive the development of new delivery systems. Current momentum in the invention of new drug delivery systems hold a promise towards much improved therapies for the treatment of vision threatening disorders.

In vitro and in vivo evaluation of carboplatin delivery to the eye using hydrogel-iontophoresis

PURPOSE

To investigate in vitro and in vivo hydrogel-iontophoresis delivery of carboplatin to the eye.

METHODS

Iontophoresis was applied on agar gels resembling the eye using different current intensities and durations. Transscleral iontophoresis was performed on healthy rabbits, applying 0, 1, and 3 mA current for 10 min.

RESULTS

Similar drug concentrations were obtained in all experimental groups, in in vitro and in vivo studies, regardless of the iontophoretic current applied. A 20-mm penetration depth was found for carboplatin at the agar model. High drug levels were found at the sclera and retina, while lower levels were found at ocular fluids.

CONCLUSION

Carboplatin-iontophoretic application at the above conditions does not have an obvious advantage over passive penetration due to high diffusion properties and insufficient molecular charge. Passive carboplatin diffusion from loaded hydrogels inserted in the lower cul-de-sac should be further investigated as a potential clinical treatment for intraocular retinoblastoma.

Methotrexate delivery to the eye using transscleral hydrogel iontophoresis

PURPOSE

To evaluate methotrexate penetration and distribution profile in ocular structures after short low current transscleral hydrogel iontophoresis.

METHODS

Methotrexate iontophoresis was studied in rabbits using drug-loaded hydrogels mounted on a portable iontophoretic device. Drug distribution profile was evaluated 2, 4, and 8 hours after iontophoretic treatment of 1.6 mA/cm2 for 4 min. Ocular drug levels were also determined two hours after iontophoretic treatment of 5 mA/cm2, compared to mock iontophoresis and intravitreal injection of methotrexate.

RESULTS

Therapeutic drug levels were maintained for at least 8 h at the sclera and retina and for 2 h at the aqueous humor following the iontophoretic treatment. After increasing the current density, a twice-higher concentration was achieved at the vitreous and 8 to 20 time higher concentrations at the retina and sclera.

CONCLUSIONS

A short low current non-invasive iontophoretic treatment using methotrexate-loaded hydrogels has a potential clinical value in treating ocular inflammatory diseases and intraocular lymphoma.

Electrically Assisted Ocular Gene Therapy

Electrotransfer and iontophoresis are being developed as innovative non-viral gene delivery systems for the treatment of eye diseases. These two techniques rely on the use of electric current to allow for higher transfection yield of various ocular cell types in vivo. Short pulses of relatively high-intensity electric fields are used for electrotransfer delivery, whereas the iontophoresis technique is based on the application of low voltage electric current. The basic principles of these techniques and their potential therapeutic application for diseases of the anterior and posterior segments of the eye are reviewed. Iontophoresis has been found most efficient for the delivery of small nucleic acid fragments such as antisense oligonucleotides, siRNA, or ribozymes. Electrotransfer, on the other hand, is being developed for the delivery of oligonucleotides or custom designed plasmids. The wide range of strategies already validated and the potential for targeting specific types of cells confirm the promising early observations made using electrotransfer and iontophoresis. These two nonviral delivery systems are safe and can be used efficiently for targeted gene delivery to ocular tissues in vivo. At the present, their application for the treatment of ocular human diseases is nearing its final stages of adaptation and practical implementation at the bedside.

Chemical modification and formulation approaches to elevated drug transport across cell membranes

Drug delivery across cellular barriers, such as intestinal, nasal, buccal, alveolar, vaginal, ocular and blood-brain, is a challenging task. Multiple physiological mechanisms, such as cellular organisation, efflux, and chemical and enzymatic degradation, as well as physicochemical properties of the drug molecule itself, determine the penetration of xenobiotics across epithelial cell layers. Limited intestinal absorption of many novel and highly potent lead compounds has stimulated an intense search for strategies that can effectively enhance permeation across these biological barriers. This review discusses some of the approaches that have been, and are currently being, investigated for transepithelial drug delivery. Transdermal drug delivery requires a separate discussion on its own and is thus outside the scope of this review article.

Iontophoresis: a non-invasive ocular drug delivery

Iontophoresis as a non-invasive technique for ocular drug delivery has been investigated for many years. This paper provides an overview of the approaches currently used in the development of the ocular iontophoretic device, the essential features of this procedure and the reported toxicity. This review focuses on the experimental results after transcorneal and transscleral iontophoresis of different drugs, emphasizing the current density applied and the treatment duration used by the investigators.

Iontophoretic drug delivery using the IOMED Phoresor®system

Iontophoresis, or electromotive drug administration, is a process that enhances the delivery of drugs through a biological membrane via the application of low-intensity electrical current. This technology offers several advantages over oral and injection drug delivery. Key advantages of iontophoretic drug delivery include the avoidance of pain and potential for infection associated with needle injection, the ability to control the rate of drug delivery, the ability to programme the drug-delivery profile and the minimisation of local tissue trauma. Research using iontophoresis has shown delivery of a number of drug classes. By controlling the applied electric current one can tailor a dosage regimen with a drug delivery profile specific for an indication and the needs of the patient. Advances in iontophoretic electrode design, microelectronics and methods to optimise iontophoretic drug delivery have improved the ability to safely deliver both older, off-patent drugs, as well as new chemical entities being developed to treat a variety of diseases. In addition to transdermal applications, current research indicates that iontophoresis may prove to be a viable noninvasive drug delivery method for treating conditions that affect the back of the eye.

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.

In vitro and in vivo characterization of scleral implant of indomethacin: role of plasticizer and cross-linking time

Film-type scleral implants of indomethacin using sodium alginate and PEG 400 and 600 (3, 5, 8, and 10% w/w w.r.t. sodium alginate) as plasticizers were fabricated by solvent casting. The prepared implants were cross-linked by treatment with calcium chloride 10, 20, and 30% w/v solution, for periods between 1 to 24 hr. Uniformity of thickness, weight, and drug content and surface pH of the implants were evaluated. The influence of plasticizer type/concentration and crosslinking time/concentration of calcium chloride on indomethacin release was studied on a static dissolution setup developed by us. Selected batches of the implants were subjected to pharmacodynamic studies, after scleral placement, in uveitis-induced (intravitreal injection of bovine serum albumin 50 microg/ml) rabbit eyes. The release of indomethacin from the implants was influenced by the concentration and nature of plasticizers used. Chemical cross-linking with calcium chloride was successful in retarding the drug release. The pharmacodynamic studies showed a marked improvement in the various clinical parameters (congestion, keratitis, flare, clot, aqueous cells, and synechias) in the implanted eye when compared with the control eye in the rabbits. The implants survived for 2 weeks in vivo.

Transscleral drug delivery to the retina and choroid

Rapid advances in the molecular pathogenesis of retinal and choroidal disorders have highlighted the urgent need for innovative drug delivery modalities to the loci of pathology. In vitro and in vivo studies suggest that the transscleral route may offer a means to achieve the goal of sustained, targeted drug delivery to the posterior segment. Potentially therapeutic concentrations of macromolecules with retention of bioactivity can be attained in the choroid and retina via minimally invasive transscleral delivery.