Ocular pharmacokinetic/ pharmacodynamic modeling for bunazosin after instillation into rabbits

Computational modeling of drug transport across the in vitro cornea

A novel quasi-3D (Q3D) modeling approach was developed to model networks of one dimensional structures like tubes and vessels common in human anatomy such as vascular and lymphatic systems, neural networks, and respiratory airways. Instead of a branching network of the same tissue type, this approach was extended to model an interconnected stack of different corneal tissue layers with membrane junction conditions assigned between the tissues. The multi-laminate structure of the cornea presents a unique barrier design and opportunity for investigation using Q3D modeling. A Q3D model of an in vitro rabbit cornea was created to simulate the drug transport across the cornea, accounting for transcellular and paracellular pathways of passive and convective drug transport as well as physicochemistry of lipophilic partitioning and protein binding. Lipophilic Rhodamine B and hydrophilic fluorescein were used as drug analogs. The model predictions for both hydrophilic and lipophilic tracers were able to match the experimental measurements along with the sharp discontinuities at the epithelium-stroma and stroma-endothelium interfaces. This new modeling approach was successfully applied towards pharmacokinetic modeling for use in topical ophthalmic drug design.

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.

Ocular pharmacokinetic/pharmacodynamic modeling for multiple anti-glaucoma drugs

We have constructed a new ocular pharmacokinetic pharmacodynamic (PK/PD) model for anti-glaucoma drugs to describe ocular hypotensive effects on intraocular pressure (IOP) after instillation of a combination of an alpha(1)-adrenergic antagonist, bunazosin, and a beta-adrenergic antagonist, timolol, into rabbits. This model was constructed by the combination of two ocular PK/PD models for bunazosin and timolol by including aqueous humor dynamics based on both action mechanisms. We also verified the reliability of this model by confirming the drug concentrations in aqueous humor and ocular hypotensive effects after instillation of the drug combination. The aqueous humor concentrations of timolol and bunazosin were determined by an HPLC, and ocular hypotensive effect-time profiles were measured using a telemetry system, which was able to record automatically detailed effects. The combined model could simulate the aqueous humor concentrations of both drugs and the additive IOP-lowering effect after instillation of the combination using the MULTI (RUNGE) program and PK/PD parameters which were obtained from ocular hypotensive effects after instillation of bunazosin alone or timolol alone. The theoretical concentration curves of both drugs in the aqueous humor and the theoretical ocular hypotensive effect curves almost agreed with both the observed concentrations and ocular hypotensive effects after instillation of the drug combination. These results indicate the reliability and usefulness of PK/PD modeling considering aqueous humor dynamics to predict IOP in multidrug therapy. This is the first study to develop a PK/PD model for multidrug therapy for the eye.

Recent advances in pharmacokinetic modeling

A major part of the science of pharmacokinetics is the modeling of the underlying processes that contribute to drug disposition. The purpose of pharmacokinetic models is to summarize the knowledge gained in preclinical and clinical studies at various stages in drug development and to rationally guide future studies with the use of adequately predictive models. This review highlights a variety of recent advances in mechanistic pharmacokinetic modeling. It is aimed at a broad audience, and hence, an attempt was made to maintain a balance between technical information and practical applications of pharmacokinetic modeling. It is hoped that drug researchers from all disciplines would be able to get a flavor of the function and capacity of pharmacokinetic modelers and their contribution to drug development. While this review is not intended to be a technical reference on modeling approaches, the roles of statistical applications and population methodologies are discussed where appropriate.

Ability of Poly-L-arginine to Enhance Drug Absorption into Aqueous Humor and Vitreous Body after Instillation in Rabbits

The effect of poly-L-arginine with a molecular weight of 35.5 kDa (PLA) on the ocular absorption of hydrophilic molecules after instillation was examined in rabbits in vivo. FITC-labeled dextran (3.8 kDa, FD-4) and pyridoxamine were used as model hyprophilic molecules for absorption. The potential toxicity of PLA was evaluated by microscopic observation of the cornea, production of TNF-alpha, and the thickness of the corneal epithelia and stroma. The concentration of pyridoxamine and FD-4 in aqueous humor 30 min after a single instillation of a solution of PLA was 29- and 16-fold higher than that without PLA, respectively, but the drug concentrations were not determined in the vitreous body. Repetitive instillation of PLA every 30 min for 150 min achieved 31.1- and 13.3-fold increases in pyridoxamine and FD-4 in aqueous humor, respectively. Furthermore, significant amounts of pyridoxamine and FD-4 were detected in the vitreous body after the repetitive instillation of PLA, even although very little of these drugs was detected in the vitreous body in the control eye without PLA. On the other hand, repetitive instillation of PLA did not induce any alteration of corneal epithelial and stromal thickness, production of TNF-alpha, and disruption of the epithelial and stromal morphologies and neutrophil infiltration. Our findings suggest that PLA may be useful in promoting drug delivery of hydrophilic drugs to the ocular tissues without producing any significant corneal damage and inflammation.