Modelling ocular pharmacokinetics of fluorescein administered as lyophilisate or conventional eye drops

Effect of aging on heat transfer, fluid flow and drug transport in anterior human eye: A computational study

There are a lot of geometrical and morphological changes that happen in the human eye with age. Primary open-angle glaucoma, which is caused by the increase in intraocular pressure inside the anterior chamber of the eye is also associated with the physiological aging of the eye. Therefore, it is crucial to understand the effects of aging on drug delivery in the human eye when applied topically. Consequently, a numerical model of topical drug delivery for an aging human eye has been developed using commercial software COMSOL Multiphysics in the current study. Three different age groups (young, middle and old) have been considered and the changes in geometrical and tissue properties of different domains of the eye with age have been included in the numerical model. The effect of aging on heat transfer, aqueous humor flow, intraocular pressure and drug concentration in different domains and orientations of the eye have been investigated. Additionally, an attempt has been made to predict the best class of anti-glaucomatic treatment in silico that should be preferred to treat primary open-angle glaucoma effectively. Results illustrate that there is a decrease in the average corneal temperature and an increase in the temperature deviation across the cornea with age. Further, there is a decrease in the aqueous humor flow magnitude in the anterior chamber of the eye and an increase in intraocular pressure in the anterior chamber of older age groups, which leads to primary open-angle glaucoma. The reduced aqueous humor flow leads to increased drug concentration in the anterior chamber as well as iris and reduced drug concentration in the trabecular mesh of the older age groups, thereby affecting the treatment efficacy. Additionally, our simulated results demonstrate that anti-glaucomatic treatments should be more focused on treating the trabecular mesh rather than the ciliary body of the eye.

Electrospun nanofibers - A promising solid in-situ gelling alternative for ocular drug delivery

A serious problem of the treatment of eye diseases is the very short residence time of the drug. The majority of the drug is cleared within few seconds due to the poor capability of the eye to accommodate additional liquids. We developed a new ocular drug delivery system, which is applied in dry form and forms immediately a gel after administration. The system is based on gellan gum/pullulan electrospun nanofibers. The rheological behavior of the spinning solution was investigated followed by further characterization of the in situ formed gel. Three-dimensional X-ray imaging with nanometric resolution (nano-CT) and electron scanning microscopy were used for a detailed characterization of the diameter and alignment of the fibers. A high porosity (87.5 ± 0.5%) and pore interconnectivity (99%) was found. To ensure a good fit to the eye anatomy, the prepared fibers were shaped into curved geometries. Additionally, a new innovative moistening chamber for the in vitro determination of the ocular residence time in porcine eyes was developed which mimics the tear turnover. A clear prolongation of the fluorescein residence time compared to conventional eye drops was achieved with the application of the curved nanofiber in situ gelling mat. In summary, the developed in situ gelling system with adapted geometry is a promising alternative system for ocular drug delivery.

Population Pharmacokinetic Modeling of Azithromycin Eyedrops in Tears Following Single-Dose Topical Administration in Healthy Volunteers

BACKGROUND AND OBJECTIVES

The disposition of azithromycin in the human eye following topical administration has not been fully explored. Population pharmacokinetic (PopPK) modeling can allow useful conclusions to be drawn based on limited tear sampling data. The aim of this study was therefore to develop and evaluate a PopPK model of azithromycin eyedrops in tears, investigate typical model parameters, and identify potential covariates following single-dose ocular instillation.

METHODS

A total of 84 tear samples were obtained from 42 healthy volunteers at seven time points over 24 h following topical administration of azithromycin eyedrops (2.5 mL/25 mg). Azithromycin concentrations in the tears were determined using a validated LC-MS/MS assay. PopPK analysis was performed using nonlinear mixed-effects modeling. Intraocular pressure, tear secretion measurement, age, and gender were evaluated as possible covariates. Bootstrap and visual predictive checks were used simultaneously to evaluate the PopPK model. The dosage regimen was further estimated based on Monte Carlo simulation and the area under the curve/minimal inhibitory concentration.

RESULTS

A linear two-compartment first-order elimination model was found to best describe the pharmacokinetic profile of azithromycin in tears. None of the covariates had a significant influence on the typical model parameters. The final PopPK model was demonstrated to be suitable and effective according to bootstrap and visual predictive checks. Twice-daily instillation of azithromycin eyedrops would appear to provide the required antibacterial activity.

CONCLUSION

A proposed linear two-compartment PopPK model of azithromycin eyedrops was found to be effective at describing the disposition of azithromycin in tears after ocular instillation.

Ocular Drug Distribution After Topical Administration: Population Pharmacokinetic Model in Rabbits

BACKGROUND AND OBJECTIVE

When eye diseases are treated by topical administration, the success of treatment lies in the effective drug concentration in the target tissue. This is why the drug's pharmacokinetic, in the different substructures of the eye, needs to be explored more accurately during drug development. The aim of the present analysis was to describe by rabbit model, the distribution of a drug after ocular instillation in the selected eye tissues and fluids.

METHODS

By a top-down population approach, we developed and validated a population pharmacokinetics (PopPK) model, using tissue concentrations (tear, naso-lacrymal duct, cornea and aqueous humor) of a new src tyrosine kinase inhibitor (FV-60165) in each anterior segment's tissue and fluid of the rabbit eye. Inter-individual variability was estimated and the impact of the formulation (solution or nanosuspension) was evaluated.

RESULTS

The model structure selected for the eye is a 4-compartment model with the formulation as a significant covariate on the first-order rate constant between tears and the naso-lacrymal duct. The model showed a good predictive performance and may be used to estimate the concentration-time profiles after single or repeated administration, in each substructure of the eye for each animal included in the analysis.

CONCLUSIONS

This analysis allowed describing the distribution of a drug in the different selected tissues and fluids in the rabbit's eyes after instillation of the prodrug as a solution or nanosuspension.

A New Spray Device to Deliver Topical Ocular Medication: Penetration of Fluorescein to the Anterior Segment

PURPOSE

To measure the penetration of fluorescein into the anterior ocular compartments after exposure of the cornea to a mist of aerosol droplets.

METHODS

This was an open-label proof-of-principle trial. Eighteen healthy volunteers were asked to participate. A conventional (50 μL) drop of fluorescein solution (20 mg/mL) was administered to the right eye; an ocular mist (10 μL) of the same solution was applied to the left eye. Autofluorescence (photons/s) was measured in the cornea, the anterior chamber (AC), and the lens before administration and at 1, 2, 5, 10, 20, 50, and 100 min thereafter. The area under the curve (AUC) was calculated. For the vitreous cavity, measurements were performed at baseline and after 100 min.

RESULTS

All participants completed the study. AUC (mean±SD) for the cornea was (363±431)×10(4) photons after drop application and (154±265)×10(4) photons after the mist (P=0.005). For the AC, these values were (6.9±10.3)×10(4) and (2.9±5.4)×10(4) photons, respectively (P=0.14). Autofluorescence data obtained in the lens did not allow reliable AUC calculations. Autofluorescence in the vitreous at 100 min did not significantly exceed the level at baseline.

CONCLUSION

It was demonstrated that fluorescein applied to the ocular surface with the spray device enters the AC. The total amount of fluorescein molecules reaching the ocular surface by the 2 methods of administration, however, is not equivalent. Therefore, no definitive conclusions on relative bioavailability can be drawn from this experiment.