In situ measurement of fluorescein release by collagen shields in human eyes

Corneal epithelial permeability to fluorescein in humans by a multi-drop method

Purpose

The permeability of the corneal epithelium to fluorescein P_dc is an indicator of the health of the ocular surface. It can be measured in a clinical setting by determining the accumulation of fluorescein in the stroma following administration of the dye on the ocular surface. Here we demonstrate a new multi-drop method for the measurement of P_dc by a spot fluorometer.

Methods

Twenty-nine healthy participants were recruited for this study. First, a probe-drop of fluorescein (0.35%, 2 μL) was instilled on the conjunctiva. The clearance of the dye from the tears was immediately measured using the fluorometer. Following this, two loading drops (2%; 6 μL each) were administered 10 min apart. Fifteen minutes later, the ocular surface was washed and fluorescence from the stroma F_s was measured. Permeability was calculated using P_dc = (Q x F_s)/ (2 x AUC), where Q is the stromal thickness and AUC is the area under the fluorescence vs. time curve for the loading drops.

Results

After the probe drop, the tear fluorescence followed an exponential decay (elimination rate constant; k_d = 0.41 ± 0.28 per min; 49 eyes of 29 subjects), but the increase in F_s was negligible. However, after the loading drops, the measured F_s was ~ 20-fold higher than the autofluorescence and could be recorded at a high signal to noise ratio (SNR > 40). The intra-subject variability of k_d was insignificant. Since fluorescein undergoes concentration quenching at > 0.5%, the value of AUC for the loading drops was estimated by scaling the AUC of the probe drop. The calculated P_dc was 0.54 ± 0.54 nm/sec (n = 49). A Monte Carlo simulation of the model for the multi-drop protocol confirmed the robustness of the estimated P_dc.

Conclusions

The new multi-drop method can be used in place of the single-drop approach. It can overcome a lack of sensitivity in fluorometers of high axial resolution. The P_dc estimated by the multi-drop method is ~ 11-fold higher than previously reported but closer to the value reported for other drugs with equivalent octanol/water partition coefficient.

Ocular translational science: A review of development steps and paths

Developing successful drug delivery methods is challenging for any tissue, and the eye is no exception. Translating initial concepts into advanced technologies treating diseases in preclinical models and finally into functional and marketable products for humans can be particularly daunting. While referring to specific ophthalmic companies and products, this review considers key exchanges that lead to successful translation. By building on basic science discoveries in the academic setting, applied science can perform proof-of-concept work with simple, benchtop experiments. Eventually, simple models need to be translated to more robust ones where cells, tissues, and entire organisms are incorporated. Successful translation also includes performing due diligence of the intellectual property, understanding the market needs, undertaking clinical development, meeting regulatory requirements, and eventually scale up manufacturing. Different stages of the translation can occur in different environments, including moving from academia to industry, from one company to another, or between veterinary and human applications. The translation process may also rely on contract organizations to move through the complex landscape. While the path to a commercial, marketable product may not look the same each time, it is important to design a development plan with clear goals and milestones to keep on track.

In vitro controlled release of an anti-inflammatory from daily disposable therapeutic contact lenses under physiological ocular tear flow

Novel molecularly imprinted, therapeutic contact lenses capable of controlled release of the non-steroidal anti-inflammatory (NSAID) diclofenac sodium were synthesized, exploiting ionic non-covalent interactions. Poly(HEMA-co-DEAEM-co-PEG200DMA) soft contact lenses were prepared (105±5 μm thickness, diameter 15.0±0.2mm, base curve of 8.6±0.2mm) with different monomer to template ratios and dynamic release studies were conducted in artificial lacrimal solution using two different in vitro methods. Under infinite sink conditions, imprinted contact lenses demonstrated concentration dependent release kinetics. Under physiological flow rates, by increasing the M/T ratio from 1 to 10.5, the release rate decreased from 11.72 μg/h to 6.75 μg/h during the first 48 h. The release rate was more constant, moving toward zero-order release. To use these lenses as daily disposable lenses, the first 24h of release was studied and found to be linear with a rate of 17.27, 11.99, and 8.74 μg/h for M/T ratios of 1, 3.5, and 10.5, respectively. Furthermore, the lenses prepared with a M/T ratio of 10.5 released diclofenac at a rate close to the maximum dose delivered by commercial eye drops, making them ideal for use as daily disposable lenses, and potentially leading to better patient benefit with substantially increased efficacy.

Zero-order therapeutic release from imprinted hydrogel contact lenses within in vitro physiological ocular tear flow

Zero-order or concentration independent release kinetics are highly desirable from drug delivery devices. In this paper we demonstrate experimentally, for the first time, zero-order release of a small molecular weight therapeutic, ketotifen fumarate (MW=425), from molecularly imprinted hydrogels used as therapeutic contact lenses. We performed dynamic, in vitro drug release studies from imprinted hydrogel contact lenses within a novel microfluidic device that simulates the volumetric flow rates, tear volume and tear composition of the eye. Imprinted gels with multiple functional monomers and complexation points to the drug demonstrated a significantly delayed release of drug compared to less functionalized systems. There were no statistical differences in experimentally determined equilibrium swollen polymer volume fractions, which correlate with molecular weight between crosslinks and mesh size of the gel. Under infinite sink conditions, imprinted contact lenses demonstrated Fickian (concentration dependent) release kinetics with diffusion coefficients ranging from 4.04 x 10(-9) to 5.57 x 10(-10) cm(2)/s. The highest functionalized gel exhibited a diffusion coefficient averaging ten times smaller than less functionalized gels and released drug for over 5 days with 3 distinct rates of release. Under physiological volumetric flow rates, the release rate was constant for a duration of 3.5 days delivering a therapeutically relevant dosage and was fit to a power law model indicating zero-order release characteristics with n=0.981+/-0.006 (r(2)=0.997). This work demonstrates the potential of micro/nanofluidic devices to determine physiological release rates and stresses the importance of matching local conditions to adequately characterize drug delivery devices. It also demonstrates the enormous potential for molecular imprinting to further tailor therapeutic release kinetics via the imprinting process.

Collagen Shields as a Drug Delivery System for the Fourth-Generation Fluoroquinolones

PURPOSE

To evaluate the penetration of commercially available gatifloxacin and moxifloxacin into the anterior chamber of a rabbit eye using collagen shields presoaked in the antibiotics as a drug delivery system.

METHODS

Collagen shields, presoaked for 10 min in commercially available solutions of gatifloxacin (diluted intravenous Tequin) or moxifloxacin (Vigamox) with the same concentration, were placed on the surface of each of the corneas of 12 rabbits for a total of 24 eyes (12 in each group). Aqueous humor samples were taken 3 and 6 h later.

RESULTS

The concentrations of both antibiotics were high after 3 h (3.1 +/- 1.3 microg/ml for moxifloxacin and 2.3 +/- 0.8 microg/ml for gatifloxacin, p = 0.22). The concentration of gatifloxacin after 6 h was statistically significantly higher than for moxifloxacin (0.76 +/- 0.33 microg/ml vs. 0.29 + 0.14 microg/ml, respectively, p = 0.03).

CONCLUSION

Our results suggest that collagen shields can be effective as a drug delivery system for the fourth-generation fluoroquinolones with a longer effect for gatifloxacin.