Protocol for evaluation of topical ophthalmic drug products in different compartments of fresh eye tissues in a rabbit model

Quantitative systems pharmacology of the eye: Tools and data for ocular QSP

Good eyesight belongs to the most-valued attributes of health, and diseases of the eye are a significant healthcare burden. Case numbers are expected to further increase in the next decades due to an aging society. The development of drugs in ophthalmology, however, is difficult due to limited accessibility of the eye, in terms of drug administration and in terms of sampling of tissues for drug pharmacokinetics (PKs) and pharmacodynamics (PDs). Ocular quantitative systems pharmacology models provide the opportunity to describe the distribution of drugs in the eye as well as the resulting drug-response in specific segments of the eye. In particular, ocular physiologically-based PK (PBPK) models are necessary to describe drug concentration levels in different regions of the eye. Further, ocular effect models using molecular data from specific cellular systems are needed to develop dose-response correlations. We here describe the current status of PK/PBPK as well as PD models for the eyes and discuss cellular systems, data repositories, as well as animal models in ophthalmology. The application of the various concepts is highlighted for the development of new treatments for postoperative fibrosis after glaucoma surgery.

Application of vibrational spectroscopy and nuclear magnetic resonance methods for drugs pharmacokinetics research

OBJECTIVES

The development of new methods for determining the concentration of drugs is an actual topic today. The article contains a detailed review on vibrational spectroscopy and nuclear magnetic resonance methods using for pharmacokinetic research. This study is devoted to the possibility of using vibrational spectroscopy and 1H nuclear magnetic resonance spectroscopy to determine the concentration of drugs and the use of these groups of techniques for therapeutic drug monitoring.

CONTENT

The study was conducted by using scientific libraries (Scopus, Web of Science Core Collection, Medline, GoogleScholar, eLIBRARY, PubMed) and reference literature. A search was conducted for the period from 2011 to 2021 in Russian and English, by combinations of words: 1H nuclear magnetic resonance (¹H NMR), vibrational spectroscopy, Surface-Enhanced Raman spectroscopy, drug concentration, therapeutic drug monitoring. These methods have a number of advantages and are devoid of some of the disadvantages of classical therapeutic drug monitoring (TDM) methods - high performance liquid chromatography and mass spectrometry. This review considers the possibility of using the methods of surface-enhanced Raman scattering (SERS) and ¹H NMR-spectroscopy to assess the concentration of drugs in various biological media (blood, urine), as well as to study intracellular metabolism and the metabolism of ophthalmic drugs. ¹Н NMR-spectroscopy can be chosen as a TDM method, since it allows analyzing the structure and identifying metabolites of various drugs. ¹Н NMR-based metabolomics can provide information on the side effects of drugs, predict response to treatment, and provide key information on the mechanisms of action of known and new drug compounds.

SUMMARY AND OUTLOOK

SERS and ¹Н NMR-spectroscopy have great potential for further study and the possibility of introducing them into clinical practice, including for evaluating the efficacy and safety of drugs.

Mechanistic modeling of ophthalmic, nasal, injectable, and implant generic drug products: A workshop summary report

For approval, a proposed generic drug product must demonstrate it is bioequivalent (BE) to the reference listed drug product. For locally acting drug products, conventional BE approaches may not be feasible because measurements in local tissues at the sites of action are often impractical, unethical, or cost-prohibitive. Mechanistic modeling approaches, such as physiologically-based pharmacokinetic (PBPK) modeling, may integrate information from drug product properties and human physiology to predict drug concentrations in these local tissues. This may allow clinical relevance determination of critical drug product attributes for BE assessment during the development of generic drug products. In this regard, the Office of Generic Drugs of the US Food and Drug Administration has recently established scientific research programs to accelerate the development and assessment of generic products by utilizing model-integrated alternative BE approaches. This report summarizes the presentations and panel discussion from a public workshop that provided research updates and information on the current state of the use of PBPK modeling approaches to support generic product development for ophthalmic, injectable, nasal, and implant drug products.

Clinical Ocular Exposure Extrapolation for Ophthalmic Solutions Using PBPK Modeling and Simulation

BACKGROUND

The development of generic ophthalmic drug products is challenging due to the complexity of the ocular system, and a lack of sensitive testing to evaluate the interplay of physiology with ophthalmic formulations. While measurements of drug concentration at the site of action in humans are typically sparse, these measurements are more easily obtained in rabbits. The purpose of this study is to demonstrate the utility of an ocular physiologically based pharmacokinetic (PBPK) model for translation of ocular exposure from rabbit to human.

METHOD

The Ocular Compartmental Absorption and Transit (OCAT™) model within GastroPlus® v9.8.2 was used to build PBPK models for levofloxacin (Lev), moxifloxacin (Mox), and gatifloxacin (Gat) ophthalmic solutions. in the rabbit eye. The models were subsequently used to predict Lev, Mox, and Gat exposure after ocular solution administrations in humans. Drug-specific parameters were used as fitted and validated in the rabbit OCAT model. The physiological parameters were scaled to match human ocular physiology.

RESULTS

OCAT model simulations for rabbit well described the observed concentrations in the eye compartments following Lev, Mox, and Gat solution administrations of different doses and various administration schedules. The clinical ocular exposure following ocular administration of Lev, Mox, and Gat solutions at different doses and various administration schedules was well predicted.

CONCLUSION

Even though additional case studies for different types of active pharmaceutical ingredients (APIs) and formulations will be needed, the current study represents an important step in the validation of the extrapolation method to predict human ocular exposure for ophthalmic drug products using PBPK models.

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.

Bibliometric analysis of articles on nanoemulsion and/or in-situ gel for ocular drug delivery system published during the 2011–2021 period

The bibliometric data were extracted from the Scopus database to investigate the conceptual framework of ocular nanoemulsion and/or in-situ gel drug delivery system using “ocular” AND “nanoemulsion” OR “in-situ gel” keywords. The data were evaluated with RStudio and VOSviewer program.

The results reveal that the publication trends tend to increase continually. India is the most impactful country, and the most constructive institution is Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Cairo University. International Journal of Pharmaceutics is the top influential source. Ali A is the most prolific author. The title of the most impactful article was In-situ gelling systems based on Pluronic F127/Pluronic F68 formulations for ocular drug delivery”. “Controlled release” is the most popular keyword.

These results provide insights for stimulating research collaborations and revealing open issues of controlled-release ocular preparation to overcome an ocular barrier and enhance patient compliance.

Quantification of Drugs in Distinctly Separated Ocular Substructures of Albino and Pigmented Rats

The rat is a commonly used species in ocular drug research. Detailed methods of separating rat ocular tissues have not been described in literature. To understand the intraocular drug distribution, we developed a robust method for the separation of individual anterior and posterior substructures of pigmented Brown Norway (BN) and albino Wistar Han (WH) rat eyes, followed by quantification of drug concentration in these substructures. A short formalin incubation, which did not interfere with drug quantification, enabled the preservation of individual tissue sections while minimizing cross-tissue contamination, as demonstrated by histological analysis. Following oral administration, we applied the tissue separation method, in order to determine the ocular concentrations of dexamethasone and levofloxacin, as well as two in-house molecules BI 113823 and BI 1026706, compounds differing in their melanin binding. The inter-individual variability in tissue partitioning coefficients (Kp) was low, demonstrating the reproducibility of the separation method. Kp values of individual tissues varied up to 100-fold in WH and up to 46,000-fold in BN rats highlighting the importance of measuring concentration directly from the ocular tissue of interest. Additionally, clear differences were observed in the BN rat tissue partitioning compared to the WH rat. Overall, the developed method enables a reliable determination of small molecule drug concentrations in ocular tissues to support ocular drug research and development.

In vitro physicochemical characterization and dissolution of brinzolamide ophthalmic suspensions with similar composition

The quality of an ophthalmic suspension is crucial for its in vivo performance, and often impact product's effectiveness. An in-depth understanding of critical quality attributes (CQAs) of ophthalmic suspensions such as particle size distribution (PSD) and rheology, as well as the impact of these CQAs on product performance are important for successful product development, quality control, and regulatory approval. This study employed brinzolamide ophthalmic suspension, 1%, as a model ophthalmic product, and six batches were manufactured using an innovative planetary centrifugal milling (PCM) process. Three batches were manufactured to have distinctly different PSD. These three batches had qualitatively (Q1) and quantitatively (Q2) the same composition as the model drug product (i.e., Azopt), while the differences in PSD were introduced by changing only the manufacturing process parameters. On the other hand, changes in rheology were introduced by altering the input level of the viscosity enhancing polymer in the formulation. A systematic approach was employed to understand the relation between manufacturing process parameters, CQAs, and in vitro product performance. Among the evaluated CQAs, PSD, rheology, surface tension, and drug dissolution were found more sensitive to the changes in the manufacturing processes. Most notably, we developed a rapid dissolution method (completed within minutes) employing in-situ fiber optic UV dissolution system. This novel dissolution method mimics the environmental conditions of the eye such as dissolution under "non-sink" condition and under high shear (from blinking). The method was highly discriminatory to differences in the PSD in the suspension. This study also revealed an important relation between the PSD of the suspension and its rheology which originated as a result of an interaction at the molecular level between the solid drug particles and the viscosity enhancing polymers. These findings underscore the need to evaluate CQAs of the ophthalmic suspensions in concert rather than separately when comparing ophthalmic drug products and product performance.

Investigating the ocular toxicity potential and therapeutic efficiency of in situ gel nanoemulsion formulations of brinzolamide

Glaucoma is an ocular disease i.e. more common in older adults with elevated intraocular pressure and a serious threat to vision if it is not controlled. Due to the limitations regarding the conventional form of brinzolamide (Azopt®), two optimum formulations of in situ gel nanoemulsion were developed. To ensure the safety and efficacy of developed formulations for ocular drug delivery, the current study was designed. MTT assay was carried out on the human retinal pigmentation epithelial cells. To investigate the irritation potential of the chosen formulations, hen's egg test-chorioallantoic membrane as a borderline test between in vivo and in vitro methods has been done. The modified Draize method was utilized to evaluate eye tolerance against the selected formulations. Intraocular pressure was measured by applying the prepared formulations to the eyes of normotensive albino rabbits in order to assess the therapeutic efficacy. Based on MTT test, cell viability for NE-2 at 0.1% and NE-1 at 0.1 and 0.5% concentrations was acceptable. The results of the hen's egg test-chorioallantoic membrane test indicated no sign of vessel injury on the chorioallantoic membrane surface for both formulations. Also, during 24 h, both formulations were well-tolerated by rabbit eyes. The pharmacodynamics effects of formulations had no difference or were even higher than that of suspension in case of adding lower concentration (0.5%) of brinzolamide to the formulations. With regard to the results of the mentioned methods, our advanced formulations were effective, safe, and well-tolerated, thus can be introduced as an appropriate vehicle for ocular delivery of brinzolamide.

A Novel Eyes Topical Drug Delivery System: CsA-LNC for the Treatment of DED

PURPOSE

The objective of the present work was to prepare safe and effective Ciclosporin A Lipid nanocapsule (CsA-LNC) eye-drops for the treatment of DED.

METHODS

The phase-inversion method was used to prepared different sizes CsA-LNC. CsA biodistribution in ocular after topical administration in rabbits was analyzed by a validated UPLC-MS/MS method. The efficacy of CsA-LNCs (25 nm, 50 nm, 85 nm) was evaluated using the tear breakup time, fluorescein staining, tear production, inflammatory cytokines and histopathology tests. The safety of CsA-LNCs was study by the score of ocular irritation and histological examination study.

RESULTS

CsA-LNCs(20-100 nm) were successfully prepared, An in vivo PK study showed significant improvement of the bioavailability (4.20-fold (25 nm), 2.15-fold (50 nm) and 2.33-fold (85 nm)) in bulbar conjunctiva, and great permeability was observed in the cornea for CsA-LNCs compared with CsA emulsion. An in vivo PD study showed that CsA-LNCs have great efficacy for DED, and the effect was improved over CsA emulsion. CsA-LNCs were safe and not cause significant irritation to the eyes surface of rabbits.

CONCLUSION

This work has demonstrated CsA-LNCs, in particular small sizes CsA-LNC, are safe and effective with promising potential to treat DED. Grapical abstract.

Physiologically Based Pharmacokinetic Model to Support Ophthalmic Suspension Product Development

FDA's Orange Book lists 17 currently marketed active pharmaceutical ingredients (API) formulated within ophthalmic suspensions in which a majority has 90% or more of the API undissolved. We used an ocular physiologically based pharmacokinetic (O-PBPK) model to compare a suspension with a solution for ophthalmic products with dexamethasone (Dex) as the model drug. Simulations with a Dex suspension O-PBPK model previously verified in rabbit were used to characterize the consequences of drug clearance mechanism in the precorneal compartment on pharmacokinetic (PK) exposure and to assess the ocular and systemic PK characteristics of ophthalmic suspensions with different strengths or magnitudes of viscosity. O-PBPK-based simulations show that (1) Dex suspension 0.05% has a 2.5- and 5-fold higher AUC in aqueous humor and plasma, respectively, than the Dex saturated solution; (2) strength increase by 5- and 10-fold induces a respective 2.2- and 3.3-fold increase in aqueous humor and 4.4- and 8.6-fold increase in plasma C_max and AUC; and (3) increasing formulation viscosity (from 1.6 to 75 cP) causes an overall increase in API available for absorption in the cornea resulting in a higher ocular C_max and AUC with no significant impact on systemic exposure. This research demonstrates that solid particles present in a suspension can not only help to achieve a higher ocular exposure but also unfavorably raise systemic exposure. A model able to correlate formulation changes to both ocular and plasma exposure is a necessary tool to support ocular product development taking into consideration both local efficacy and systemic safety aspects.

Application of Mechanistic Ocular Absorption Modeling and Simulation to Understand the Impact of Formulation Properties on Ophthalmic Bioavailability in Rabbits: a Case Study Using Dexamethasone Suspension

Developing mathematical models to predict changes in ocular bioavailability and pharmacokinetics due to differences in the physicochemical properties of complex topical ophthalmic suspension formulations is important in drug product development and regulatory assessment. Herein, we used published FDA clinical pharmacology review data, in-house, and literature rabbit pharmacokinetic data generated for dexamethasone ophthalmic suspensions to demonstrate how the mechanistic Ocular Compartmental Absorption and Transit model by GastroPlus™ can be used to characterize ocular drug pharmacokinetic performance in rabbits for suspension formulations. This model was used to describe the dose-dependent (0.01 to 0.1%) non-linear pharmacokinetic in ocular tissues and characterize the impact of viscosity (1.67 to 72.9 cP) and particle size (5.5 to 22 μm) on in vivo ocular drug absorption and disposition. Parameter sensitivity analysis (hypothetical suspension particle size: 1 to 10 μm, viscosity: 1 to 100 cP) demonstrated that the interplay between formulation properties and physiological clearance through drainage and tear turnover rates in the pre-corneal compartment drives the ocular drug bioavailability. The quick removal of drug suspended particles from the pre-corneal compartment renders the impact of particle size inconsequential relative to viscosity modification. The in vivo ocular absorption is (1) viscosity non-sensitive when the viscosity is high and the impact of viscosity on the pre-corneal residence time reaches the maximum physiological system capacity or (2) viscosity sensitive when the viscosity is below a certain limit. This study reinforces our understanding of the interplay between physiological factors and ophthalmic formulation physicochemical properties and their impact on in vivo ocular drug PK performance in rabbits.