Topical pharmacokinetics of brinzolamide suspensions in rabbits and variability analysis for sample size and design considerations.

Identifying critical attributes for complex locally acting ophthalmic formulations and establishing in vitro-in vivo correlations can facilitate selection of appropriate thresholds for formulation changes that reflect lack of impact on in vivo performance. In this study the marketed antiglaucoma product Azopt® (1% brinzolamide suspension) and five other brinzolamide formulations varying in particle size distributions and apparent viscosities were topically administered in rabbits, and their ocular pharmacokinetics was determined in multiple ocular tissues. Statistical evaluation with ANOVA showed no significant differences between the formulations in the peak drug concentration (Cmax) in the aqueous humor and iris-ciliary body. As a post-hoc analysis, the within animal and total variability was determined for Cmax in the aqueous humor and iris-ciliary body. Based on the observed variability, we investigated the sample size needed for two types of study designs to observe statistically significant differences in Cmax. For the sample size calculations, assuming both 25% and 50% true differences in Cmax between two formulations, two study designs were compared: paired-eye dosing design (one formulation in one eye and another formulation in the other eye of the same animal at the same time) versus parallel-group design. The number of rabbits needed in the paired-eye dosing design are much lower than in the parallel-group design. For example, when the true difference in aqueous humor Cmax is 25%, nine rabbits are required in the paired-eye design versus seventy rabbits (35 per treatment) in the parallel-group design to observe a statistically significant difference with a power of 80%. Therefore, the proposed paired-eye dosing design is a viable option for the design of pharmacokinetic studies comparing ophthalmic products to determine the impact of formulation differences.

Pharmacokinetics of Sirolimus in a Novel Liposome Delivery System in Selected Ocular Tissues and Plasma Following a Single Subconjunctival Injection in Dutch Belted Rabbits.

Purpose: To determine the pharmacokinetics of a proprietary liposomal sirolimus (LS) formulation in ocular tissues and plasma following a single subconjunctival (SCJ) injection in Dutch belted rabbits (DBR). Analytical methods for detection of LS in plasma, aqueous humor (AH), vitreous humor (VH), retina, combined retina/choroid/retinal pigment epithelium, sclera, and iris/ciliary body were developed to examine samples. Methods: Thirty male DBR were subconjunctivally injected in both eyes with 0.1 mL of LS of 1,000 µg/mL. At selected times post-injection, ocular tissues and whole blood samples were obtained. Sirolimus concentrations were measured using liquid chromatography/tandem mass spectrometry. Results: No LS was detected in serum or AH at any time. All other examined ocular tissues had quantifiable amounts of LS at all times. LS levels were highest in sclera and lowest in VH, suggesting LS followed the supraciliary and suprachoroidal spaces to reach the posterior segment. Vitreous peak of sirolimus levels occurred at 2 h, and the sclera adjacent to the injection peaked at both 2 and 96 h. LS levels in remaining ocular tissues peaked at 6 h and decreased with time, persisting at presumed therapeutic levels on day 22. Conclusions: LS can quickly diffuse into posterior intraocular tissues after SCJ injection without reaching quantifiable levels in AH or serum in DBR. Peak levels occurred in posterior intraocular tissues at 6 h and persisted in all tissues after 3 weeks. SCJ LS in DBR is safe, has a stable pharmacokinetic profile, and should be considered for further study in human trials for autoimmune ophthalmopathies.

Characterization and validation of a chronic retinal neovascularization rabbit model by evaluating the efficacy of anti-angiogenic and anti-inflammatory drugs.

AIM: To establish a rabbit model with chronic condition of retinal neovascularization (RNV) induced by intravitreal (IVT) injection of DL-2-aminoadipic acid (DL-AAA), a retinal glial (Müller) cell toxin, extensive characterization of DL-AAA induced angiographic features and the suitability of the model to evaluate anti-angiogenic and anti-inflammatory therapies for ocular vascular diseases. METHODS: DL-AAA (80 mmol/L) was administered IVT into both eyes of Dutch Belted rabbit. Post DL-AAA delivery, clinical ophthalmic examinations were performed weekly following modified McDonald-Shadduck Scoring System. Color fundus photography, fluorescein angiography (FA), and optical coherence tomography (OCT) procedures were performed every 2 or 4wk until stable retinal vascular leakage was observed. Once stable retinal leakage (12wk post DL-AAA administration) was established, anti-vascular endothelial growth factor (VEGF) (bevacizumab, ranibizumab and aflibercept) and anti-inflammatory (triamcinolone, TAA) drugs were tested for their efficacy after IVT administration. Fluorescein angiograms were scored before and after treatment following a novel grading system, developed for the DL-AAA rabbit model. RESULTS: Post DL-AAA administration, eyes were presented with moderate to severe retinal/choroidal inflammation which was accompanied by intense vitreous flare and presence of inflammatory cells in the vitreous humor. Retinal hemorrhage was restricted to the tips of neo-retinal vessels. FA revealed maximum retinal vascular leakage at 2wk after DL-AAA injection and then persisted as evidenced by stable mean FA scores in weeks 8 and 12. Retinal vascular angiographic and tomographic features were stable and consistent up to 36mo among two different staggers induced for RNV at two different occasions. Day 7, mean FA scores showed that 1 µg/eye of bevacizumab, ranibizumab, aflibercept and 2 µg/eye of TAA suppress 65%, 90%, 100% and 50% retinal vascular leakage, respectively. Day 30, bevacizumab and TAA continued to show 66% and 44% suppression while ranibizumab effect was becoming less effective (68%). In contrast, aflibercept was still able to fully (100%) suppress vascular leakage on day 30. On day 60, bevacizumab, ranibizumab and TAA showed suppression of 7%, 12%, and 9% retinal vascular leakage, respectively, however, aflibercept continued to be more effective showing 50% suppression of vascular leakage. CONCLUSION: The DL-AAA rabbit model mimics RNV angiographic features like RNV and chronic retinal leakage. Based on these features the DL-AAA rabbit model provides an invaluable tool that could be used to test the therapeutic efficacy and duration of action of novel anti-angiogenic formulations, alone or in combination with anti-inflammatory compounds.

Topical pharmacokinetics of dexamethasone suspensions in the rabbit eye: Bioavailability comparison.

Topical corticosteroids are used to treat inflammation of the anterior segment. Due to their low water-solubility, they are often formulated as suspensions, but ocular bioavailability of the suspensions is not known. Herein, ocular pharmacokinetics of dexamethasone in albino rabbits was investigated following intracameral administration of dexamethasone solution and topical administration of three commercial suspensions: Maxidex®, TobraDex®, and TobraDexST®. Dexamethasone concentrations in tear fluid, cornea, aqueous humor, conjunctiva and iris-ciliary body were determined. Non-compartmental analysis was performed to estimate the pharmacokinetic parameters of dexamethasone. Following intracameral administration, the clearance and the apparent volume of distribution were estimated to be 13.6 µL/min and 990 µL, respectively. After topical administration, the absolute aqueous humor bioavailability for dexamethasone (<2%) is being reported for the first time. The highest value was obtained for TobraDexST® followed by Maxidex® and TobraDex®. This study provides for the first-time comprehensive and quantitative ocular pharmacokinetic parameters (including absolute bioavailability) for topically instilled dexamethasone suspensions. Furthermore, the new intracameral pharmacokinetic parameters allow a rational and quantitative basis for the design of improved ocular dexamethasone delivery systems.

The Effect of Sodium Iodide on Stromal Loading, Distribution and Degradation of Riboflavin in a Rabbit Model of Transepithelial Corneal Crosslinking.

PURPOSE: To evaluate effects of sodium iodide (NaI) on riboflavin concentration in corneal stroma before and during ultraviolet A (UVA) light exposure using a novel transepithelial corneal collagen crosslinking (CXL) procedure (EpiSmart CXL system, CXL Ophthalmics, Encinitas CA). METHODS: Riboflavin solutions with NaI (Ribostat, CXL Ophthalmics, Encinitas CA) and without NaI were used for CXL in rabbits using EpiSmart. A pilot study determined sufficient riboflavin loading time. Four rabbits were dosed and monitored. Riboflavin fluorescence intensity was assessed from masked slit-lamp photos. A 12 min loading time was selected. Sixteen additional rabbits received the two formulae in contralateral eyes for CXL. Riboflavin uptake was assessed at 0, 10, 15, 20, 25, and 30 min of UVA exposure using a scale for riboflavin fluorescence previously validated against stromal concentration. Post sacrifice, corneal stromal samples were analyzed for concentrations of riboflavin and riboflavin 5'-phosphate. RESULTS: Eyes dosed with NaI riboflavin had higher riboflavin grades compared to eyes dosed with the NaI-free riboflavin formulation immediately after riboflavin loading and persisting throughout UVA exposure, with significantly higher (P < 0.01 to < 0.05) riboflavin grades from 15 through 25 min of UVA exposure. Riboflavin grades decreased more slowly in eyes dosed with NaI riboflavin through 25 minutes of UVA exposure. Minor conjunctival irritation was noted with or without NaI. CONCLUSION: The addition of NaI to riboflavin solution is associated with increased riboflavin concentration in corneal stroma throughout a clinically relevant time course of UVA exposure. This effect may be a combination of enhanced epithelial penetration and reduced riboflavin photodegradation and should enhance intrastromal crosslinking.

Comprehensive Ocular and Systemic Pharmacokinetics of Brinzolamide in Rabbits After Intracameral, Topical, and Intravenous Administration.

Brinzolamide is a topical carbonic anhydrase inhibitor which reduces the production of aqueous humor in the ciliary body, thereby reducing intra-ocular pressure. It is formulated as an ophthalmic suspension. The pharmacokinetics of ocular suspensions is not well understood. The objective of this study was to characterize the pharmacokinetics of brinzolamide in rabbit aqueous humor, iris-ciliary body, plasma, and whole blood. New Zealand White rabbits were dosed via intracameral, topical and intravenous administration. After intracameral administration (4.5 µg) of solubilized brinzolamide, aqueous humor concentrations were described with a two-compartment model, the estimated clearance was 4.12 µL/min, apparent volume of distribution at steady-state 673 µL, and terminal half-life 3.4 h. After topical administration of 1% brinzolamide suspension (500 µg), absolute bioavailability based on aqueous humor AUC0-∞ was 0.10%. After intravenous administration of brinzolamide solution (0.75 mg/kg) elimination half-life in plasma and whole blood appeared to be over two weeks. The ratios of the measured concentrations of irisciliary body to whole blood, to plasma, and to aqueous humor concentrations enabled direct comparisons, and helped identify the significant contribution of the conjunctival-scleral pathways of absorption to the ciliary body. This study shows for the first-time the absolute bioavailability in aqueous humor and provides comprehensive pharmacokinetic parameters following administration of a topical suspension.

Correction to: Sustained and targeted episcleral delivery of celecoxib in a rabbit model of retinal and choroidal neovascularization.

[This corrects the article DOI: 10.1186/s40942-018-0131-1.].

Sustained and targeted episcleral delivery of celecoxib in a rabbit model of retinal and choroidal neovascularization.

Background: To evaluate the efficacy of selective episcleral delivery of celecoxib formulated in a sustained-release episcleral exoplant on a model of retinal and choroidal neovascularization induced in rabbits by subretinal injection of matrigel combined with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Methods: Nine New Zealand white rabbits were randomly assigned to three groups (episcleral celecoxib exoplant, intravitreal bevacizumab injection and control group). The bFGF was mixed with matrigel at a concentration of 10 ug/0.1 mL, and VEGF was mixed with matrigel at a concentration of 2 ug/0.1 mL. Animals assigned to celecoxib or intravitreal bevacizumab groups were treated within 03 days from matrigel injection. Fluorescein angiography (FA) and electroretinography (ERG) were performed 5 days, 2, 4 and 8 weeks after matrigel injection. Persistence or regression of three clinical features (subretinal hyperfluorescence, retinal vascular tortuosity and retinal fibrotic spots) was independently evaluated in each study group at all follow-up periods. Statistical analysis using Fisher's exact test was performed to compare the frequency of findings at each time point between treated groups and control. Results: In all study eyes, matrigel induced the appearance of subretinal blebs and the development of retinal and subretinal neovascularization characterized by progressive and late hyperfluorescence on FA. Persistence of subretinal hyperfluorescence was higher in non-treated (control) animals compared to celecoxib (p = 0.0238) treated animals. The mean b-wave amplitude ratios of ERG recordings did not reveal statistically significant differences between the study groups. Control animals retained in average 40% (± 7%) of the pre-treatment recorded b-wave amplitude, compared to 53% (± 29%) after bevacizumab and 53% (± 17%) after celecoxib treatment. Conclusion: In this rabbit model of retinal and subretinal neovascularization, episcleral celecoxib delivery was demonstrated to significantly inhibit neovascularization. It was also noticed, although not statistically significant, an apparent effect of episcleral celecoxib on preventing tractional retinal detachment secondary to epiretinal fibrovascular proliferation. The transscleral delivery of celecoxib combined with sustained-release strategy may have impact in the treatment of retinal and choroidal proliferative diseases.

Quantitative analysis of corneal stromal riboflavin concentration without epithelial removal.

PURPOSE: To compare the corneal stromal riboflavin concentration and distribution using 2 transepithelial corneal crosslinking (CXL) systems. SETTING: Absorption Systems, San Diego, California, USA. DESIGN: Experimental study. METHODS: The stromal riboflavin concentration of 2 transepithelial CXL systems was compared in rabbit eyes in vivo. The systems were the Paracel/Vibex Xtra, comprising riboflavin 0.25% solution containing TRIS and ethylenediaminetetraacetic acid and an isotonic solution of riboflavin 0.25%, (Group 1) and the CXLO system (Group 2). Manufacturers' Instructions For Use were followed. The intensity of riboflavin fluorescence by slitlamp observation 10, 15, and 20 minutes after instillation was graded on a scale of 0 to 5. The animals were humanely killed and the corneal stromal samples analyzed with liquid chromatography and mass spectrometry. RESULTS: The mean riboflavin fluorescence intensity grades in Group 1 (4 eyes) were 3.8, 4.8, and 4.8 at 10, 15, and 20 minutes, respectively. The mean grades in Group 2 (3 eyes) were 2.0, 2.3, and 2.0, respectively. The riboflavin distribution was uniform in Group 1 but not in Group 2. The mean riboflavin concentration by liquid chromatography and mass spectrometry was 27.0 µg/g stromal tissue in Group 1 and 6.7 µg/g in Group 2. A stromal riboflavin concentration theoretically adequate for CXL, 15 µg/g, was achieved in all eyes in Group 1 and no eyes in Group 2. Slitlamp grading correlated well with liquid chromatography and mass spectrometry concentration (R2 = 0.940). CONCLUSIONS: The system used in Group 1 produced corneal riboflavin concentrations that were theoretically adequate for effective transepithelial CXL (≥15 µg/g), while the system in Group 2 did not. Slitlamp grading successfully estimated the corneal riboflavin concentration and can be used to ensure an adequate concentration of riboflavin in the cornea for transepithelial CXL.

Topical Cross-Linked HA-Based Hydrogel Accelerates Closure of Corneal Epithelial Defects and Repair of Stromal Ulceration in Companion Animals.

Purpose: The purpose of this study was to determine the safety of topical ocular administration of a cross-linked, modified hyaluronic acid (xCMHA-S) hydrogel, and its effectiveness in accelerating repair and closure of acute and nonhealing corneal ulcers in companion animals as a veterinary treatment and its utility as a model for therapy in human corneal ulceration. Methods: Two concentrations of xCMHA-S (0.33% and 0.75%) were topically administered to the eyes of rabbits six times daily for 28 days to assess safety. Then, 30 dogs and 30 cats with spontaneous acute corneal ulcers were treated with either xCMHA-S (0.75%) or a non-cross-linked hyaluronic acid (HA) solution (n = 15 per group for each species), three times daily until the ulcer had healed. Finally, 25 dogs with persistent nonhealing corneal ulcers were treated with xCMHA-S (0.75%) twice daily until the ulcer had healed. Results: Both concentrations of the xCMHA-S hydrogel were well tolerated, safe, and nontoxic in the 28-day exaggerated dosing study in healthy rabbits. Topically applied xCMHA-S significantly accelerated closure of acute corneal stromal ulcers in dogs and cats compared with a non-cross-linked HA solution. Further, topical administration of the xCMHA-S aided in closure of nonhealing corneal stromal ulcers in dogs. Conclusions: Hyaluronic acid has previously been shown to aid in corneal wound repair. This study demonstrates that a cross-linked, modified HA hydrogel provides further benefit by accelerating time to corneal wound closure compared to a non-cross-linked HA solution in companion animals, and therefore may be beneficial in fulfilling an unmet need in humans.

Effect of sedation with xylazine and ketamine on intraocular pressure in New Zealand white rabbits.

To determine the effects of intravenous and intramuscular xylazine-ketamine on intraocular pressure (IOP) in laboratory rabbits, 10 New Zealand white rabbits received xylazine (0.46 mg/kg) and ketamine (1.5 mg/kg) intravenously whereas another 10 rabbits received intramuscular xylazine (10 mg/kg) and ketamine (50 mg/kg). IOP was measured at baseline and 5, 10, 20, and 25 min after administration in rabbits that were injected intravenously and at baseline and 10, 20, 30, and 45 min in rabbits injected intramuscularly. Baseline IOP (mean ± 1 SD; intravenous group, 20.15 ± 2.24 mm Hg; intramuscular group, 19.03 ± 1.77 mm Hg) did not differ between groups. Compared with baseline values, IOP decreased significantly after intravenous administration at 10, 20, and 25 min (decreases of 2.73, 4.10, and 4.55 mm Hg, respectively) but not at 5 min (decrease of 1.40 mm Hg). IOP in intramuscularly dosed rabbits showed significant differences from baseline at 10, 20, 30, and 45 min (decreases of 2.88, 3.30, 3.95, and 4.60 mm Hg, respectively). In the intravenous group, IOP differed at 10 min compared with 25 min (1.83 mm Hg, P = 0.0143) but not at 20 min compared with 25 min (0.450 mm Hg). In the intramuscular group, differences in IOP at 10 min compared with 20 min, 20 min compared with 30 min, and 30 min compared with 45 min were nonsignificant. Intravenous and intramuscular xylazine-ketamine decreased IOP in laboratory rabbits and may be used safely during ocular procedures for which increased IOP is a concern.