A review of topically administered mini-tablets for drug delivery to the anterior segment of the eye

Overview of processed excipients in ocular drug delivery: Opportunities so far and bottlenecks

Ocular drug delivery presents a unique set of challenges owing to the complex anatomy and physiology of the eye. Processed excipients have emerged as crucial components in overcoming these challenges and improving the efficacy and safety of ocular drug delivery systems. This comprehensive overview examines the opportunities that processed excipients offer in enhancing drug delivery to the eye. By analyzing the current landscape, this review highlights the successful applications of processed excipients, such as micro- and nano-formulations, sustained-release systems, and targeted delivery strategies. Furthermore, this article delves into the bottlenecks that have impeded the widespread adoption of these excipients, including formulation stability, biocompatibility, regulatory constraints, and cost-effectiveness. Through a critical evaluation of existing research and industry practices, this review aims to provide insights into the potential avenues for innovation and development in ocular drug delivery, with a focus on addressing the existing challenges associated with processed excipients. This synthesis contributes to a deeper understanding of the promising role of processed excipients in improving ocular drug delivery systems and encourages further research and development in this rapidly evolving field.

Study of Diminutive Granules as Feed Powders for Manufacturability of High Drug Load Minitablets

The maximal amount of drug contained in a minitablet is limited. To reduce the total number of minitablets in a single dose, high drug load minitablets can be prepared from high drug load feed powders by various pharmaceutical processing techniques. Few researchers have however examined the influence of pharmaceutical processing techniques on the properties of high drug load feed powders, and consequently the manufacturability of high drug load minitablets. In this study, silicification of the high drug load physical mix feed powders alone did not yield satisfactory quality attributes and compaction parameters to produce good quality minitablets. The abrasive nature of fumed silica increased ejection force and damage to the compaction tools. Granulation of fine paracetamol powder was crucial for the preparation of good quality high drug load minitablets. The diminutive granules had superior powder packing and flow properties for homogenous and consistent filling of the small die cavities when preparing minitablets. Compared to the physical mix feed powders for direct compression, the granules which possessed higher plasticity, lower rearrangement and elastic energies, yielded better quality minitablets with high tensile strength and rapid disintegration time. High shear granulation demonstrated greater process robustness than fluid bed granulation, with less discernment on the quality attributes of feed powder. It could proceed without fumed silica, with the high shear forces reducing interparticulate cohesivity. An in-depth understanding on the properties of high drug load feed powders with inherently poor compactability and poor flowability is important for the manufacturability of high drug load minitablets.

Aqueous Prostaglandin Eye Drop Formulations

Glaucoma is one of the leading causes of irreversible blindness worldwide. It is characterized by progressive optic neuropathy in association with damage to the optic nerve head and, subsequently, visual loss if it is left untreated. Among the drug classes used for the long-term treatment of open-angle glaucoma, prostaglandin analogues (PGAs) are the first-line treatment and are available as marketed eye drop formulations for intraocular pressure (IOP) reduction by increasing the trabecular and uveoscleral outflow. PGAs have low aqueous solubility and are very unstable (i.e., hydrolysis) in aqueous solutions, which may hamper their ocular bioavailability and decrease their chemical stability. Additionally, treatment with PGA in conventional eye drops is associated with adverse effects, such as conjunctival hyperemia and trichiasis. It has been a very challenging for formulation scientists to develop stable aqueous eye drop formulations that increase the PGAs' solubility and enhance their therapeutic efficacy while simultaneously lowering their ocular side effects. Here the physiochemical properties and chemical stabilities of the commercially available PGAs are reviewed, and the compositions of their eye drop formulations are discussed. Furthermore, the novel PGA formulations for glaucoma treatment are reviewed.

3D printing in Ophthalmology: From medical implants to personalised medicine

3D printing was invented thirty years ago. However, its application in healthcare became prominent only in recent years to provide solutions for drug delivery and clinical challenges, and is constantly evolving. This cost-efficient technique utilises biocompatible materials and is used to develop model implants to provide a greater understanding of human anatomy and diseases, and can be used for organ transplants, surgical planning and for the manufacturing of advanced drug delivery systems. In addition, 3D printed medical devices and implants can be customised for each patient to provide a more tailored treatment approach. The advantages and applications of 3D printing can be used to treat patients with different eye conditions, with advances in 3D bioprinting offering novel therapy applications in ophthalmology. The purpose of this review paper is to provide an in-depth understanding of the applications and advantages of 3D printing in treating different ocular conditions in the cornea, glaucoma, retina, lids and orbits.

Lyophilized ophthalmologic patches as novel corneal drug formulations using a semi-solid extrusion 3D printer

3D printing technology is a novel and practical approach for producing unique and complex industrial and medical objects. In the pharmaceutical field, the approval of 3D printed tablets by the US Food and Drug Administration has led to other 3D printed drug formulations and dosage forms being proposed and investigated. Here, we report novel ophthalmologic patches for controlled drug release fabricated using a semi-solid material extrusion-type 3D printer. The patch-shaped objects were 3D printed using hydrogel-based printer inks composed of hypromellose (HPMC), sugar alcohols (mannitol, xylitol), and drugs, then freeze-dried. The viscous properties of the printer inks and patches were dependent on the HPMC and sugar alcohol concentrations. Then, the physical properties, surface structure, water uptake, antimicrobial activity, and drug release profile of lyophilized patches were characterized. Lyophilized ophthalmologic patches with different dosages and patterns were fabricated as models of personalized treatments prepared in hospitals. Then, ophthalmologic patches containing multiple drugs were fabricated using commercially available eye drop formulations. The current study indicates that 3D printing is applicable to producing novel dosage forms because its high flexibility allows the preparation of patient-tailored dosages in a clinical setting.

Comparative Analysis of Morphological and Release Profiles in Ocular Implants of Acetazolamide Prepared by Electrospinning

The visual impairment that often leads to blindness causes a higher morbidity rate. The goal of this work is to create a novel biodegradable polymeric implant obtained from coaxial fibers containing the dispersed drug-acetazolamide-in order to achieve sustained drug release and increase patient compliance, which is of the highest importance. Firstly, during this work, uncoated implants were produced by electrospinning, and rolled in the shape of small cylinders that were composed of uniaxial and coaxial fibers with immobilized drug inside. The fibers were composed by PCL (poly ε-caprolactone) and Lutrol F127 (poly (oxyethylene-b-oxypropylene-b-oxyethylene)). The prepared implants exhibited a fast rate of drug release, which led to the preparation of new implants incorporating the same formulation but with an additional coating film prepared by solvent casting and comprising PCL and Lutrol F127 or PCL and Luwax EVA 3 ((poly (ethylene-co-vinyl acetate)). Implants were characterized and in vitro release profiles of acetazolamide were obtained in phosphate buffered saline (PBS) at 37 °C. The release profile of the acetazolamide from coated implant containing Luwax EVA 3 is considerably slower than what was observed in case of coated implants containing Lutrol F127, allowing a sustained release and an innovation relatively to other ocular drug delivery systems.

Public Knowledge, Attitude, and Perception Toward Conventional and Novel Ocular Treatment in Malaysia

One of the major concerns in any pharmacological treatment is the patients’ adherence to medication. However, different types of ocular dosage forms might result in different response and compliance from the patients. This study investigated and compared public willingness on different types of dosage forms available for ocular treatment. The study also evaluated their willingness on new approach for the treatment based on their knowledge, attitude, and perception. This study was conducted between October and December 2017 through a set of questionnaires applied to 90 respondents between the age of 18 and 60 years who lived in Muar and Kuantan, Malaysia. The results were analyzed using SPSS software version 22.0 including inferential and descriptive statistics. There was no significant difference in the knowledge level between all age groups towards different types of dosage forms available; eye drops (P = 0.09), eye ointment (P = 0.252), medicated contact lens (P = 0.05), ocular mini-tablets (P = 0.06), and ocular inserts (P = 0.075). There is a variation of results among the public towards different types of dosage forms with their willingness to try conventional and novel approach. Eye drops show the highest willingness followed by eye ointment (less willingness). However, most of them showed no willingness towards medicated contact lens, ocular mini-tablets, and ocular insert. This research hopes to provide an overview on the development process of new formulation and dosage forms based on the patients’ willingness level in an attempt to increase patient compliance.

Comparative Assessment of Distribution Characteristics and Ocular Pharmacokinetics of Norvancomycin Between Continuous Topical Ocular Instillation and Hourly Administration of Eye Drop

Background

The aim of this study was to compare the distribution characteristics and ocular pharmacokinetics of norvancomycin (NVCM) in ocular tissues of the anterior segment between continuous topical ocular instillation and hourly administration of eye drop in rabbits.

Methods

Sixty rabbits were randomly divided into two groups: continuous topical ocular instillation drug delivery (CTOIDD) group and eye drop (control) group. In the CTOIDD group, NVCM solution (50 mg/mL) was perfused to the ocular surface using the CTOIDD system at 2 mL/h up to 10 h and the same solution was administered at one drop (50 μL) per hour for 10 h in the control group. Animals (N=6 per time-point per group) were humanely killed at 2, 4, 6, 10, and 24 h to analyze their ocular tissues and plasma. The concentrations of NVCM in the conjunctiva, cornea, aqueous humour, iris, ciliary body and plasma were measured by HPLC with photodiode array detector. The pharmacokinetic parameters were calculated by Kinetica 5.1.

Results

The highest concentrations of NVCM for the CTOIDD group and control group were 2105.45±919.89 μg/g and 97.18±43.14 μg/g in cornea, 3033.92±1061.95 μg/g and 806.99±563.02 μg/g in conjunctiva, 1570.19±402.87 μg/g and 46.93±23.46 μg/g in iris, 181.94±47.11 μg/g and 15.38±4.00 μg/g in ciliary body, 29.78±4.90 μg/mL and 3.20±1.48 μg/mL in aqueous humour, and 26.89±5.57 μg/mL and 1.90±1.87 μg/mL in plasma, respectively. The mean NVCM levels significantly increased at all time-points in cornea, iris, and ciliary body (p<0.05) in the CTOIDD group. The AUC_0–24 values in the CTOIDD group were 27,543.70 μg·h/g in cornea, 32,514.48 μg·h/g in conjunctiva, 8631.05 μg·h/g in iris, 2194.36 μg·h/g in ciliary body and 343.9 μg·h/mL in aqueous humour, which were higher than for the eye drop group in all tissues.

Conclusion

Since continuous instillation of NVCM with CTOIDD could reach significantly higher concentrations and was sustained for a longer period compared with hourly administration of eye drop, CTOIDD administered NVCM could be a possible method to treat bacterial keratitis.

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Formulation of sustained release bioadhesive minitablets containing solid dispersion of levofloxacin for once daily ocular use

This study aimed to increase ocular residence time of levofloxacin by formulation into zero-order sustained release mucoadhesive minitablets for once daily administration using a hydrophobic-hydrophilic polymeric matrix. Levofloxacin was first formulated into solid dispersion with different ratios of Eudragit^® RS then the resulting solid dispersion was mixed with different concentrations of Carbopol^® and other excipients to be finally compressed into minitablets. A 2⁴ full factorial design was employed to estimate the effects and interactions of two formulation factors, and to establish their relationships with selected responses in the developed minitablets. The studied factors were: drug to Eudragit^® RS ratio, and percent of Carbopol^® in the minitablets. Sixteen ocular minitablets formulations were prepared and evaluated for the cumulative percentages drug release at 6, 12, and 24 h, as well as mucoadhesion time, mucoadhesive strength, and swelling index as response variables. After optimizing the responses, the optimized formulation was found to be stable on sterilization using gamma-irradiation and storage at 40 °C/75% RH for six months. In vivo testing of the optimized formulation showed that the minitablets extended levofloxacin release up to 24 h without causing any ocular irritation. The optimized formulation exhibited superior microbiological activity compared to the commercial product.

Ocular Drug Delivery

Although the eye is an accessible organ for direct drug application, ocular drug delivery remains a major challenge due to multiple barriers within the eye. Key barriers include static barriers imposed by the cornea, conjunctiva, and retinal pigment epithelium and dynamic barriers including tear turnover and blood and lymphatic clearance mechanisms. Systemic administration by oral and parenteral routes is limited by static blood-tissue barriers that include epithelial and endothelial layers, in addition to rapid vascular clearance mechanisms. Together, the static and dynamic barriers limit the rate and extent of drug delivery to the eye. Thus, there is an ongoing need to identify novel delivery systems and approaches to enhance and sustain ocular drug delivery. This chapter summarizes current and recent experimental approaches for drug delivery to the anterior and posterior segments of the eye.

Strategies for Improving Ocular Drug Bioavailability and Corneal Wound Healing with Chitosan-Based Delivery Systems

The main inconvenience of conventional eye drops is the rapid washout of the drugs due to nasolacrimal drainage or ophthalmic barriers. The ocular drug bioavailability can be improved by either prolonging retention time in the cul-de-sac or by increasing the ocular permeability. The focus of this review is to highlight some chitosan-based drug delivery approaches that proved to have good clinical efficacy and high potential for use in ophthalmology. They are exemplified by recent studies exploring in-depth the techniques and mechanisms in order to improve ocular bioavailability of the active substances. Used alone or in combination with other compounds with synergistic action, chitosan enables ocular retention time and corneal permeability. Associated with other stimuli-responsive polymers, it enhances the mechanical strength of the gels. Chitosan and its derivatives increase drug permeability through the cornea by temporarily opening tight junctions between epithelial cells. Different types of chitosan-based colloidal systems have the potential to overcome the ocular barriers without disturbing the vision process. Chitosan also plays a key role in improving corneal wound healing by stimulating the migration of keratinocytes when it is used alone or in combination with other compounds with synergistic action.

Enhanced drug loading efficiency of contact lenses via salt-induced modulation

Low drug loading efficiency is one of the main obstacles hindering the application of contact lenses (CLs) as the carrier for extended ocular drug delivery. Here in this study, a simple and effective drug loading method based on salt induced modulation was proposed and demonstrated with mechanism elucidation. First of all, using poly (2-hydroxyethyl methacrylate) (p-HEMA) as the contact lens material, betaxolol hydrochloride, Diclofenac Sodium and Betaxolol Base as the model drugs with different solubility, influence of salt concentration, salt type (sodium salts of sulfate, chloride, and sulfocyanate) and drug properties in the loading solution on drug loading efficiency was investigated. Mechanism of enhanced drug loading in contact lens was further explored via studying the influence of salt on the absorption isotherm, drug solubility and water content of CLs. Applicability of this method to other CLs materials was also investigated. It was demonstrated that adjusting the ionic strength of loading solutions resulted in significant increase of drug loading in CLs. Type and concentration of the salts and solubility of the drug were the main factors influencing enhancement ratio of drug loading. The mechanism for improved drug loading was related to the reduced drug solubility in loading solutions and the reduced bound water content in contact lenses. Modulation of drug loading by adjusting ionic strength was also applicable to other CLs and the light transmittance was not affected. This method was more suitable for salt-form drugs with high solubility. In summary, adjusting ionic strength of loading solution is an economical and effective way to improve drug loading in CLs, and this simple method may also find application in other hydrogel based drug delivery systems.

Ophthalmic drug dosage forms: characterisation and research methods

This paper describes hitherto developed drug forms for topical ocular administration, that is, eye drops, ointments, in situ gels, inserts, multicompartment drug delivery systems, and ophthalmic drug forms with bioadhesive properties. Heretofore, many studies have demonstrated that new and more complex ophthalmic drug forms exhibit advantage over traditional ones and are able to increase the bioavailability of the active substance by, among others, reducing the susceptibility of drug forms to defense mechanisms of the human eye, extending contact time of drug with the cornea, increasing the penetration through the complex anatomical structure of the eye, and providing controlled release of drugs into the eye tissues, which allows reducing the drug application frequency. The rest of the paper describes recommended in vitro and in vivo studies to be performed for various ophthalmic drugs forms in order to assess whether the form is acceptable from the perspective of desired properties and patient's compliance.