Drug-device combination approaches for delivery to the eye

Progress in Ocular Drug Delivery: Challenges and Constraints

The eye has several dynamic and static barriers in place to limit the entry of foreign substances including therapeutics. As such, efficient drug delivery, especially to posterior segment tissues, has been challenging. This chapter describes the anatomical and physiological challenges associated with ocular drug delivery before discussing constraints with regard to formulation parameters. Finally, it gives an overview of advanced drug delivery technologies with a specific focus on recently marketed and late-stage clinical trial products.

Wettability and contact angle affect precorneal retention and pharmacodynamic behavior of microspheres

In the present study, we describe the development of betaxolol hydrochloride and montmorillonite with ion exchange in a single formulation to create a novel micro-interactive dual-functioning sustained-release delivery system (MIDFDS) for the treatment of glaucoma. Betaxolol hydrochloride molecule was loaded onto the montmorillonite by ion exchange and MIDFDS formation was confirmed by XPS data. MIDFDS showed similar physicochemical properties to those of Betoptic, such as particle size, pH, osmotic pressure, and rheological properties. Nevertheless, the microdialysis and intraocular pressure test revealed better in vivo performance of MIDFDS, such as pharmacokinetics and pharmacodynamics. With regards to wettability, MIDFDS had a larger contact angle (54.66 ± 5.35°) than Betoptic (36.68 ± 1.77°), enabling the MIDFDS (2.93 s) to spread slower on the cornea than Betoptic (2.50 s). Moderate spreading behavior and oppositely charged electrostatic micro-interactions had a comprehensive influence on micro-interactions with the tear film residue, resulting in a longer precorneal retention time. Furthermore, MIDFDS had a significant sustained-release effect, with complete release near the cornea. The dual-functioning sustained-release carrier together with prolonged pre-corneal retention time (80 min) provided sufficiently high drug concentrations in the aqueous humor to achieve a more stable and long-term IOP reduction for 10 h. In addition, cytotoxicity and hemolysis tests showed that MIDFDS had better biocompatibility than Betoptic. The dual-functioning microspheres presented in this study provide the possibility for improved compliance due to low cytotoxicity and hemolysis, which suggests promising clinical implications.

Observation and Mitigation of Leachables from Non-Product Contact Materials in Electromechanical Delivery Devices for Biotechnology Products

Battery-powered drug delivery devices are widely used as primary containers for storing and delivering therapeutic protein products to improve patient compliance and quality of life. Compared to conventional delivery approaches such as pre-filled syringes, battery-powered devices are more complex in design requiring new materials/components for proper functionality, which could cause potential product safety and quality concerns from the extractable and leachables (E&L) of the new materials/components. In this study, E&L assessments were performed on a battery-powered delivery device during the development and qualification of the device, where novel compound 2‑hydroxy-2-methylpropiophenone (HMPP) and related compounds were observed in both E&L. The source of the HMPP and related compounds was identified to be the nonproduct contact device batteries, in which HMPP photo-initiator was used as a curing agent in the battery sealant to prevent leakage of the battery electrolytes. Toxicology assessment was performed, which showed the levels of HMPP observed in the device lots were acceptable relative to the permitted daily exposure. A drug product HMPP spike study was also performed, where no product impact was observed. Based on these assessments, an action threshold and specification limits could be established as a control strategy, if needed, to mitigate the potential risks associate with the observed leachables. As a full resolution, seven battery candidates from different suppliers were screened and one new battery was successfully qualified for the delivery devices. Overall, the holistic E&L approach was fully successful in the development and qualification of the battery-powered devices for biotherapeutic products delivery ensuring product quality and patient safety. Non-product contact materials are commonly rated as low or no risk and typically considered as out of scope of E&L activities for delivery systems following industry benchmark and regulatory agency guidance. This case study is novel as it brings into attention the materials that might not normally be in consideration during the development process. It is highly recommended to understand materials in the context of intended use on a case-by-case basis and not to generalize to ensure successful development and qualification.

Polymeric Implants for the Treatment of Intraocular Eye Diseases: Trends in Biodegradable and Non-Biodegradable Materials

Intraocular/Intravitreal implants constitute a relatively new method to treat eye diseases successfully due to the possibility of releasing drugs in a controlled and prolonged way. This particularity has made this kind of method preferred over other methods such as intravitreal injections or eye drops. However, there are some risks and complications associated with the use of eye implants, the body response being the most important. Therefore, material selection is a crucial factor to be considered for patient care since implant acceptance is closely related to the physical and chemical properties of the material from which the device is made. In this regard, there are two major categories of materials used in the development of eye implants: non-biodegradables and biodegradables. Although non-biodegradable implants are able to work as drug reservoirs, their surgical requirements make them uncomfortable and invasive for the patient and may put the eyeball at risk. Therefore, it would be expected that the human body responds better when treated with biodegradable implants due to their inherent nature and fewer surgical concerns. Thus, this review provides a summary and discussion of the most common non-biodegradable and biodegradable materials employed for the development of experimental and commercially available ocular delivery implants.

Thiolated cyclodextrins: Mucoadhesive and permeation enhancing excipients for ocular drug delivery

Thiolated β-cyclodextrin (β-CD) has the potential to enhance mucoadhesive and permeation enhancing properties on ocular mucosa. Thiolated β-CD was synthesized via replacement of all primary hydroxyl groups on β-CD backbone by halogen followed by substitution with thiol groups. The structure was confirmed by FT-IR and ¹H NMR spectroscopy. Thiolated CD was characterized for hemolytic effect, ocular irritation, solubility enhancement, viscoelastic behavior and mucoadhesive properties. Moreover, the permeation enhancing effect of thiolated oligomer on different ocular tissues including conjunctiva, sclera and cornea was evaluated with sodium fluorescein (Na-Flu) as a marker. Thiolated β-CD displayed 5360 ± 412 µmol/g thiol groups. The newly synthesized oligomer did not show any hemolytic effect on red blood cells at a concentration of 0.5% (m/v) for an incubation period of 3 h and minimal corneal irritation effects without any inflammation within 72 h. Thiolated β-CD exhibited a 5.3-fold improved aqueous solubility as compared to the unmodified β-CD. Thiolated oligomer (0.5% m/v) enhanced the viscosity of mucus up to 6.2-fold within 4 h and provided a 26-fold prolonged ocular residence time due to mucoadhesion. Moreover, 0.5% (m/v) thiolated β-CD enhanced the permeation of Na-Flu 9.6-, 7.1- and 5.3-fold on conjunctiva, sclera and cornea, respectively. Based on these findings, thiolated β-CD might be a promising auxiliary agent for ocular drug delivery.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part II: Cell and Tissue Engineering Therapies

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 y.o. 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 on 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, Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, different treatment options have to be considered. Cell therapy is a very promising alternative to drug-based approaches for AMD treatment. Cells delivered to the affected tissue as a suspension have shown poor retention and low survival rate. A solution to these inconveniences has been the encapsulation of these cells on biomaterials, which contrive to their protection, gives them support, and favor their retention of the desired area. We offer a two-papers 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 this second part we review the preclinical and clinical cell-replacement approaches aiming at the development of efficient AMD-therapies, the employed cell types, as well as the cell-encapsulation and cell-implant systems. We discuss their advantages and disadvantages and how they could improve the survival and integration of the implanted cells.

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.

The prominence of the dosage form design to treat ocular diseases

The eye is susceptible to various diseases commonly difficult to treat. To overcome the barriers imposed by this organ for required drugs penetration, technological strategies have been implemented to ocular formulations. Among them are the use of temperature or electric stimuli and the development of nanoparticles. The objective of this review is to present the main barriers to ocular drug delivery and to discuss strategies used in the development of ocular dosage forms, primarily for topical delivery, to increase the local bioavailability of drugs, target their delivery and increase patient compliance. Results obtained in the last years related to the topical administration of liposomes, dendrimers, iontophoresis, among other nanoparticulate systems focused on ophthalmic delivery, will be addressed. Finally, some clinical trials and marketed formulations that use nanotechnology to topically treat eye diseases will be presented.

In Vitro Topical Delivery of Chlorhexidine to the Cornea: Enhancement Using Drug-Loaded Contact Lenses and β-Cyclodextrin Complexation, and the Importance of Simulating Tear Irrigation

Microbial keratitis is a severe, sight-threatening condition caused by various pathogens. Eyedrops are the standard delivery modality for treating these disorders; however, blinking reflex, elevated tear production, and nasolacrimal drainage eliminate much of the instilled dose within a few seconds. Therefore, eyedrops must be applied repeatedly for prolonged periods. The present study aimed to probe more effective ocular delivery of chlorhexidine based upon drug-loaded hydrogel contact lenses and β-cyclodextrin (β-CD), while also determining the effect of constant irrigation with simulated tear fluid (STF) in in vitro experiments. Chlorhexidine digluconate (as 0.2 and 2% solutions, β-CD inclusion complexes, and loaded hydrogel contact lenses) were applied to enucleated porcine eyes as single or multiple 10 μL doses, or as drug-loaded contact lenses, with and without β-CD. The corneas were then excised and drug-extracted quantified by high-performance liquid chromatography (HPLC). The effect of constant irrigation by STF was evaluated to test the effect of increased tear production on corneal delivery. Potential antimicrobial activity of the delivered drug was also assessed. Results showed that drug-loaded contact lenses delivered the greatest amount of chlorhexidine into the cornea over a 24 h period, while the eyedrop solution comparator delivered the least. The β-CD significantly enhanced chlorhexidine delivery to the cornea from eyedrop solution, although contact lenses loaded with chlorhexidine-β-CD failed to enhance delivery. β-CD within the hydrogel matrix impeded drug release. Constant irrigation with STF significantly reduced the amount of drug delivered to the cornea in all cases. Chlorhexidine retained antimicrobial activity in all delivery methods. Hydrogel contact lenses loaded with chlorhexidine delivered significantly higher levels to the cornea compared to eyedrops, either multiple hourly doses or a single dose. They also offer reduced application, in particular, to a nonulcerated corneal infection. Finally, the importance of fully accounting for tear production in in vitro ocular delivery experiments was highlighted.

Comparison of thermosensitive in situ gels and drug-resin complex for ocular drug delivery: In vitro drug release and in vivo tissue distribution

Conventional ophthalmic eye drops are limited by their rapid elimination rate and short time of action. Ion exchange resin has been used to achieve sustained ocular drug delivery but the high selectivity of drug molecules restricts its broad application. In situ gel system seems to be a good strategy to address these problems but the influence of in situ gel type on the sustained release behavior and tissue distribution after ocular application is unclear. Therefore, in this study, using betaxolol hydrochloride as a model drug, poloxamer 407 and methylcellulose as the carriers, two thermosensitive in situ gel systems were prepared and characterized. Influence of formulation composition type and concentration on in vitro drug release was studied. Tissue distribution after ocular delivery of two different thermosensitive in situ gels was studied and compared with commercial BH eye drop (Betoptic S®). In vitro studies demonstrated that addition of 4% HPMC 606W in 15% P407 solution and 5% PEG4000 in 2% MC solution obtained gels with appropriate gelation temperature and similar sustained drug release rate. In vivo tissue distribution study indicated that they presented similar drug concentration in cornea, iris-ciliary and aqueous humor irrespective of gel type, with higher drug concentration achieved after 4 h compared to the commercial resin suspension eye drops. The AUC and MRT of the two in situ gel eye drops were 2 times higher than that of the commercial resin suspension eye drops in cornea. In conclusion, the two thermosensitive in situ gels have prolonged drug release after ocular drug delivery compared with ion exchange resin eye drops, implying their potential applications in clinic with broad drug adoptability.

Contact lenses as drug-delivery systems: a promising therapeutic tool

The ocular administration of drugs using traditional pharmaceutical forms, including eye drops or ointments, results in low bioavailability, as well as requiring multiple administrations per day, with the consequent danger of therapeutic non-compliance. Although, through the use of pharmaceutical technology, attempts have been made to use various solutions in order to increase bioavailability in the most common pharmaceutical forms, it has not been entirely satisfactory. In this context, contact lenses are presented as drug delivery systems that largely remedy these two major problems and offer other additional advantages. Therefore, the use of contact lenses as drug carrying systems has been increasingly investigated in recent years, as they can increase the bioavailability of these drugs, leading to an increase in therapeutic efficacy and compliance. The main techniques used to achieve this goal are included in this review, including immersion in drug solutions, use of vitamin E barriers, molecular printing, colloidal systems, etc. The most interesting results, depending on the different eye pathologies, are presented. Although the use of contact lenses as a vehicle for the release of active ingredients is a relatively novel strategy, there are already many studies and trials that support it. In any case, further research needs to be carried out to finally reach an effective, safe, and stable product that can be marketed.

Pharmacokinetics and Tissue Distribution of Pilocarpine After Application to Eyelid Skin of Rats

Extending the delivery of drugs into the eyes while reducing systemic bioavailability is of utmost importance in the management of chronic ocular diseases. Topical application onto the lower eyelid skin, as an alternative to eye drops, is seen to be a valuable strategy in the treatment of chronic eye diseases. To elucidate the critical value of delivering drugs in solution onto the eyeball through the eyelid skin, pharmacokinetic studies of pilocarpine were conducted, and the results were verified using a direct pharmacodynamic study in rats. The mean residence time of pilocarpine after topical eyelid application to the eyelid skin, conjunctiva, eyeball, and plasma were 14.9, 8.50, 6.29, and 8.11 h, respectively. Conjunctiva and eyeball concentrations of pilocarpine at 8 h were 80-fold and 8-fold higher after topical eyelid application, respectively, than those for eye drops. Pupillary constriction was sustained over 8 h after topical eyelid application. Topical eyelid skin application exhibited a localized drug absorption and specific drug accumulation in the ocular tissues. Hence, it is rational to prepare topical formulations directed onto the eyelid skin, which is suitable for drugs required for long-term treatment.

Drug delivery to the lens for the management of cataracts

Cataracts are one of the most prevalent diseases of the lens, affecting its transparency and are the leading cause of reversible blindness in the world. The clarity of the lens is essential for its normal physiological function of refracting light onto the retina. Currently there is no pharmaceutical treatment for prevention or cure of cataracts and surgery to replace the affected lens remains the gold standard in the management of cataracts. Pharmacological treatment for prevention of cataracts is hindered by many physiological barriers that must be overcome by a therapeutic agent to reach the avascular lens. Various therapeutic agents and formulation strategies are currently being investigated to prevent cataract formation as access to surgery is limited. This review provides a summary of recent research in the field of drug delivery to the lens for the management of cataracts including models used to study cataract treatments and discusses the future perspectives in the field.