The penetration and distribution of topical atropine in animal ocular tissues

Enhanced ophthalmic bioavailability and stability of atropine sulfate via sustained release particles using polystyrene sulfonate resin

Atropine sulfate (ATS) eye drops at low concentrations constitute a limited selection for myopia treatment, with challenges such as low ophthalmic bioavailability and inadequate stability. This study proposes a novel strategy by synthesizing ophthalmic sodium polystyrene sulfonate resin (SPSR) characterized by a spherical shape and uniform size for cationic exchange with ATS. The formulation of ATS@SPSR suspension eye drops incorporates xanthan gum and hydroxypropyl methylcellulose (HPMC) as suspending agents. In vitro studies demonstrated that ATS@SPSR suspension eye drops exhibited sustained release characteristics, and tropic acid, its degradation product, remained undetected for 30 days at 40 °C. The ATS levels in the tear fluids and aqueous humor of New Zealand rabbits indicated a significant increase in mean residence time (MRT) and area under the drug concentration-time curve (AUC0-12h) for ATS@SPSR suspension eye drops compared to conventional ATS eye drops. Moreover, safety assessment confirmed the non-irritating nature of ATS@SPSR suspension eye drops in rabbit eyes. In conclusion, the cation-responsive sustained-release ATS@SPSR suspension eye drops enhanced the bioavailability and stability of ATS, offering a promising avenue for myopia treatment.

Cholinergic signaling of muscarinic receptors directly involves in the neuroprotection of muscone by inducing Ca2+ antagonism and maintaining mitochondrial function

ETHNOPHARMACOLOGICAL RELEVANCE

Musk, a traditional Chinese medicine, is broadly used in inducing resuscitation and refreshing the mind, activating blood and alleviating pain. It is commonly used for the treatment of ischemic stroke, and muscone is its core medicinal component.

AIM OF THE STUDY

The aim of this study was to explore whether muscone ameliorates neuronal damage through cholinergic signaling of muscarinic receptors.

MATERIALS AND METHODS

The effects of muscone were tested in a rat model of middle cerebral artery occlusion (MCAO) as well as injured neurons induced by oxygen-glucose deprivation (OGD) in PC12 cells. Cell counting kit 8 (CCK8) assay was used to measure the cell viability, and the production of lactate dehydrogenase (LDH) and adenosine-triphosphate (ATP) were examined by kit. 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA), tetramethylrhodamine ethyl ester (TMRE) and Fluo-4 acetoxymethyl ester (Fluo-4 AM) staining were used to demonstrate effect of muscone on the reactive oxygen species (ROS) level, mitochondria membrane potential (MMP) and intracellular Ca2+ measurement in cells respectively, in which all of those staining was visualized by laser confocal microscope. For in vivo experiments, rats' cerebral blood flow was measured using laser Doppler blood flowmetry to evaluate the MCAO model, and a modified neurological severity score (mNSS) was used to assess the recovery of neurological function. Calculate infarct rate was measured by 2,3,5-Triphenyl Tetrazolium Chloride (TTC) staining. Except DCFH-DA and Fluo-4 AM staining, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl benzimidazolylcarbocyanine iodide (JC-1) staining was used to observe intracellular Ca2+ measurement in brain cells. Protein levels in cells and tissues were detected by Western blot.

RESULTS

Pretreatment with muscone significantly improved the cell viability, lactic acid production, mitochondrial membrane potential collapse and function, Ca2+ overload, ROS generation, and cell apoptosis in OGD PC12 cells. Muscone also regulated PI3K, ERK and AKT signal pathways by activating cholinergic signaling of muscarinic receptors in PC12 cells induced with OGD. More importantly, the blocking of cholinergic signaling of muscarinic receptors by atropine significantly reduces the neuroprotective effects of muscone, including the cell viability, Ca2+ efflux, and mitochondrial repair. Furthermore, muscone was found to effectively alleviate mitochondrial dysfunction and elevated levels of ROS induced by the MCAO in the brain tissue. Notably, this beneficial effect of muscone was attenuated by atropine but not by (+)-Sparteine.

CONCLUSIONS

Our study indicates that muscone exerts its neuroprotective effects by activating muscarinic receptors of cholinergic signaling, thus providing a promising therapeutic target for the treatment of OGD-induced nerve injury in stroke. The findings suggest that these treatments may hold potential benefits for stroke patients.

The effect of topical 1 % atropine on ocular dimensions and diurnal rhythms of the human eye

The effect of topical 1 % atropine on the diurnal rhythms of the human eye was investigated. Participants wore an activity monitor on Days 1-7. A set of measures (epochs) encompassing intraocular pressure (IOP), ocular biometry, and retinal imaging were obtained on Day 7 (baseline), followed by eight epochs on Day 8, and one on Day 9 from both eyes of healthy participants (n = 22, 19-25 years). The sleep time of participants (collected via actigraphy) was used as a reference in scheduling epochs. Topical 1 % atropine was instilled in the dominant eye on Day 8, 2 h after habitual wake time, using the fellow eye as control (paired-eye design). Sinusoids with a 24-h period were fitted to the data, and a non-linear mixed-effects model was used to estimate rhythmic statistics. There were no interocular differences in any of the measured parameters at baseline. Comparing pre- versus post-atropine in treated eyes revealed lower IOP, deeper anterior chamber (ACD), decreased crystalline lens thickness and shorter axial length (AL). The same trends were observed when comparing atropine-treated versus fellow control eyes, except for IOP and AL (no differences). Both atropine-treated and fellow control eyes showed significant diurnal variations in all ocular parameters, with atropine-treated eyes revealing larger AL and retinal thickness amplitudes, smaller vitreous chamber depth (VCD) amplitudes, and a significant phase advancement for ACD and VCD. There were no interocular differences in choroidal thickness rhythms. In conclusion, while ocular diurnal rhythms persisted after instillation of 1 % atropine, many rhythmic parameters were altered.

Identification of miR-671-5p and Its Related Pathways as General Mechanisms of Both Form-Deprivation and Lens-Induced Myopia in Mice

Animal models have been indispensable in shaping the understanding of myopia mechanisms, with form-deprivation myopia (FDM) and lens-induced myopia (LIM) being the most utilized. Similar pathological outcomes suggest that these two models are under the control of shared mechanisms. miRNAs play an important role in pathological development. Herein, based on two miRNA datasets (GSE131831 and GSE84220), we aimed to reveal the general miRNA changes involved in myopia development. After a comparison of the differentially expressed miRNAs, miR-671-5p was identified as the common downregulated miRNA in the retina. miR-671-5p is highly conserved and related to 40.78% of the target genes of all downregulated miRNAs. Moreover, 584 target genes of miR-671-5p are related to myopia, from which we further identified 8 hub genes. Pathway analysis showed that these hub genes are enriched in visual learning and extra-nuclear estrogen signaling. Furthermore, two of the hub genes are also targeted by atropine, which strongly supports a key role of miR-671-5p in myopic development. Finally, Tead1 was identified as a possible upstream regulator of miR-671-5p in myopia development. Overall, our study identified the general regulatory role of miR-671-5p in myopia as well as its upstream and downstream mechanisms and provided novel treatment targets, which might inspire future studies.

The Role of Atropine in Preventing Myopia Progression: An Update

Several approaches have been investigated for preventing myopia progression in children and teenagers. Among them, topical atropine has shown promising results and it is being adopted in clinical practice more and more frequently. However, the optimal formulation and treatment algorithm are still to be determined. We discuss the pharmacokinetic, pharmacodynamic, clinical, and tolerability profile revealed first by the multicenter, randomized ATOM 1 and 2 trials and, more recently, by the LAMP Study. Results from these trials confirmed the efficacy of low-concentration atropine with a concentration-dependent response. Although atropine at 0.025% and 0.05% concentrations has shown the most encouraging results in large-scale studies, these formulations are not yet commonplace in worldwide clinical practice. Moreover, their rebound effect and the possibility of reaching a stabilization effect have not been fully investigated with real-life studies. Thus, further larger-scale studies should better characterize the clinical efficacy of atropine over longer follow-up periods, in order to define the optimal dosage and treatment regimen.

Daily or Less Frequent Topical 1% Atropine Slows Defocus-Induced Myopia Progression in Contact Lens-Wearing Guinea Pigs

Purpose

This study compared the efficacy of topical 1% atropine applied daily versus every 3 days for controlling myopia progression in guinea pigs.

Methods

To induce myopia, pigmented guinea pigs (New Zealand strain, n = 38) wore monocular −10 D rigid gas-permeable (RGP) contact lenses, which were replaced after 3 weeks with −15 diopter (D) contact lenses. Animals were treated with 1% atropine either daily (Atr-QD; n = 12), or every 3 days (Atr-Q3D; n = 11), or with artificial tears (control group; n = 15). Spherical equivalent refractive error (SER) and axial length (AL) data, as well as retinal and choroidal thickness data were collected weekly.

Results

Whereas mean (±SEM) interocular differences (treated - fellow) in both SER and AL at week 0 (baseline) were similar for all groups, significant differences between the atropine-treated and control groups were evident by week 6 (SER and AL, P < 0.001). The treated eyes of the control group showed relatively more axial elongation and myopia progression than both the Atr-QD and Atr-Q3D groups. Choroidal blood vessel area also decreased over time in the treated eyes of the control group, coupled with choroidal thinning overall, with these changes being attenuated by atropine. Retinal thickness showed a developmental decrease over the treatment period but was unaffected by atropine.

Conclusions

For this defocus-induced guinea pig model of myopia, application of 1% topical atropine slows myopia progression, even when applied every 3 days.

Translational Relevance

The results from this study suggest that the frequency of dosing for topical atropine may be reduced from the widely used daily dosing regimen without loss of myopia control efficacy.

Orthokeratology Lenses Versus Administration of 0.01% Atropine Eye Drops for Axial Length Elongation in Children With Myopic Anisometropia

OBJECTIVE

To investigate the effect of orthokeratology (OK) lenses and that of 0.01% atropine eye drops on axial length (AL) elongation in children with myopic anisometropia.

METHODS

Ninety-five children with myopic anisometropia who used OK lenses (N=49) or 0.01% atropine eye drops (N=46) were enrolled in this retrospective 1-year study. For all children, the eyes with higher spherical equivalent refractive error (SER) were assigned to the H-eye subgroup, whereas the fellow eyes with lower SER were assigned to the L-eye subgroup.

RESULTS

After 1-year treatment, the mean change in the AL of H eyes and L eyes in the OK lenses group was 0.18±0.16 mm and 0.24±0.15 mm, respectively (P=0.15), and 0.28±0.20 mm and 0.25±0.18 mm, respectively (P=0.48), in the 0.01% atropine group. Multivariate regression analyses showed significant differences in AL change between H and L eyes after treatment with OK lens (P=0.03), whereas no significant difference in the 0.01% atropine (P=0.22). The change in the AL in the H-eye group was less with OK lenses than with 0.01% atropine (P=0.04), whereas there was no significant difference between the change in AL in the L-eye group between treatment with OK lens and 0.01% atropine (P=0.89).

CONCLUSIONS

In myopic anisometropic children, AL differences between 2 eyes decrease by wearing OK lenses but do not change after administration of 0.01% atropine eye drops. The increased effect of OK lenses, but not 0.01% atropine, in reducing axial elongation at 1 year in the eye with higher SER in anisometropic children warrants further investigation.

Prevention of Choroidal Thinning by 0.01% Atropine Administered 24 h Before Exposure to Hyperopic Blur in Young Myopes

Purpose: To evaluate the persistence of atropine's effect upon choroidal thickness and ocular biometrics and its interaction with hyperopic blur in a population of young adult myopes. Methods: Twenty young (aged 18-35 years) myopic participants with spherical equivalent refractive error of -0.75 to -6.00 D (mean ± SD -2.85 ± 1.64 D) had subfoveal choroidal thickness (SFCT) measurements derived from scans collected from the right eye only with a SD-OCT instrument (Copernicus SOCT-HR) before, as well as 60 min following the introduction of 3 testing conditions: (1) placebo/hyperopic (-3 D) blur, (2) placebo/hyperopic blur one day after administration of 0.01% atropine, and (3) placebo/no blur. Each combination of blur and pharmacological agent was tested on a separate day at approximately the same time of day between 9 am and 2 pm. Results: Repeated measures ANOVA revealed that hyperopic blur and placebo were associated with a decrease in choroidal thickness (mean change: -10.7 ± 2.7 μm, P < 0.001 after 60 min), whereas administration of 0.01% atropine one day before the introduction of hyperopic blur prevented the thinning of the choroid (mean change of +1.1 ± 3.7 μm after 60 min) compared to baseline (both, P > 0.05). There was also no significant difference between the baseline choroidal thickness measurements for any of the conditions tested. Conclusion: Low dose atropine can inhibit signals associated with hyperopic defocus that cause thinning of the choroid for at least 24 h after initial instillation.

The Effect of Low-Dose Atropine on Alpha Ganglion Cell Signaling in the Mouse Retina

Low-dose atropine helps to control myopia progression with few side effects. However, the impact of atropine, a non-selective muscarinic Acetylcholine (ACh) receptor antagonist, on retinal ganglion cells (RGCs) remains unclear. After immersing the cornea and adjacent conjunctiva of enucleated eyes in 0.05% (approximately 800 μM) atropine solution for 30 min, the atropine concentration reached in the retina was below 2 μM. After direct superfusion of the retina with 1 μM atropine (considering that the clinical application of 0.05% atropine eye drops will be diluted over time due to tear flow for 30 min), no noticeable changes in the morphology of ON and OFF alpha RGCs (αRGCs) were observed. Atropine affected the light-evoked responses of ON and OFF αRGCs in a dose- and time-dependent fashion. Direct application of less than 100 μM atropine on the retina did not affect light-evoked responses. The time latency of light-induced responses of ON or OFF αRGCs did not change after the application of 0.05–100 μM atropine for 5 min. However, 50 μM atropine extended the threshold of joint inter-spike interval (ISI) distribution of the RGCs. These results indicated that low-dose atropine (<0.5 μM; equal to 1% atropine topical application) did not interfere with spike frequency, the pattern of synchronized firing between OFF αRGCs, or the threshold of joint ISI distribution of αRGCs. The application of atropine unmasked inhibition to induce ON responses from certain OFF RGCs, possibly via the GABAergic pathway, potentially affecting visual information processing.

Partitioning and Spatial Distribution of Drugs in Ocular Surface Tissues

Ocular drug absorption after eye drop instillation has been widely studied, but partitioning phenomena and spatial drug distribution are poorly understood. We investigated partitioning of seven beta-blocking drugs in corneal epithelium, corneal stroma, including endothelium and conjunctiva, using isolated porcine tissues and cultured human corneal epithelial cells. The chosen beta-blocking drugs had a wide range (-1.76-0.79) of n-octanol/buffer solution distribution coefficients at pH 7.4 (Log D_7.4). In addition, the ocular surface distribution of three beta-blocking drugs was determined by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) after their simultaneous application in an eye drop to the rabbits in vivo. Studies with isolated porcine corneas revealed that the distribution coefficient (K_p) between the corneal epithelium and donor solution showed a positive relationship and good correlation with Log D_7.4 and about a 50-fold range of K_p values (0.1-5). On the contrary, K_p between corneal stroma and epithelium showed an inverse (negative) relationship and correlation with Log D_7.4 based on a seven-fold range of K_p values. In vitro corneal cell uptake showed a high correlation with the ex vivo corneal epithelium/donor K_p values. Partitioning of the drugs into the porcine conjunctiva also showed a positive relationship with lipophilicity, but the range of K_p values was less than with the corneal epithelium. MALDI-IMS allowed simultaneous detection of three compounds in the cornea, showed data in line with other experiments, and revealed uneven spatial drug distribution in the cornea. Our data indicate the importance of lipophilicity in defining the corneal pharmacokinetics and the K_p values are a useful building block in the kinetic simulation models for topical ocular drug administration.

IMI 2021 Yearly Digest

Purpose

The International Myopia Institute (IMI) Yearly Digest highlights new research considered to be of importance since the publication of the first series of IMI white papers.

Methods

A literature search was conducted for articles on myopia between 2019 and mid-2020 to inform definitions and classifications, experimental models, genetics, interventions, clinical trials, and clinical management. Conference abstracts from key meetings in the same period were also considered.

Results

One thousand articles on myopia have been published between 2019 and mid-2020. Key advances include the use of the definition of premyopia in studies currently under way to test interventions in myopia, new definitions in the field of pathologic myopia, the role of new pharmacologic treatments in experimental models such as intraocular pressure-lowering latanoprost, a large meta-analysis of refractive error identifying 336 new genetic loci, new clinical interventions such as the defocus incorporated multisegment spectacles and combination therapy with low-dose atropine and orthokeratology (OK), normative standards in refractive error, the ethical dilemma of a placebo control group when myopia control treatments are established, reporting the physical metric of myopia reduction versus a percentage reduction, comparison of the risk of pediatric OK wear with risk of vision impairment in myopia, the justification of preventing myopic and axial length increase versus quality of life, and future vision loss.

Conclusions

Large amounts of research in myopia have been published since the IMI 2019 white papers were released. The yearly digest serves to highlight the latest research and advances in myopia.

Atropine in topical formulations for the management of anterior and posterior segment ocular diseases

INTRODUCTION

Atropine is an old-known drug which is gaining increasing attention due to the myriad of therapeutic effects it may trigger on eye structures. Nevertheless, novel applications may require more adequate topical formulations.

AREAS COVERED

This review aims to gather the existing knowledge about atropine and its clinical applications in the ophthalmological field when administered topically. Atropine ocular pharmacokinetics is paid a special attention, including recent evidences of the capability of the drug to access to the posterior segment. Ocular bioavailability and systemic bioavailability are counterbalanced. Finally, limitations of traditional dosage forms and potential advantages of under investigation delivery systems are analyzed.

EXPERT OPINION

Mydriasis and cyclopegia have been widely exploited for eye examination, management of anterior segment diseases, and more recently as antidotes of chemical weapons. Improved knowledge on drug receptors and related pathways explains atropine repositioning as an outstanding tool to prevent myopia. The ease with which atropine penetrates ocular tissues is a double edged sword, that is, while it ensures therapeutic levels in the posterior segment, the unspecific distribution causes a wide variety of untoward effects. The design of formulations that can selectively deliver atropine to the target tissue for each specific application is an urgent unmet need.

Comparison of Administration of 0.02% Atropine and Orthokeratology for Myopia Control

OBJECTIVE

To compare the efficacies of 0.02% atropine eye drops and orthokeratology to control axial length (AL) elongation in children with myopia.

METHODS

In this historical control study, 247 children with myopia whose administration of 0.02% atropine (n=142) or underwent orthokeratology from an earlier study (n=105, control group) were enrolled. Data on AL and other baseline parameters were recorded at baseline and after 1 and 2 years of treatment.

RESULTS

The mean changes in AL in the first and second years of treatment were 0.30±0.21 and 0.28±0.20 mm, respectively, in the 0.02% atropine group and 0.16±0.20 and 0.20±0.16 mm, respectively, in the orthokeratology group. Axial length elongations after 2 years of treatment were 0.58±0.35 and 0.36±0.30 mm (P=0.007) in the 0.02% atropine and orthokeratology groups, respectively. Multivariate regression analyses showed that the AL elongation was significantly faster in the 0.02% atropine group than in the orthokeratology group (β=0.18, P=0.009). In multivariate regression analyses, younger age and shorter baseline AL were associated with a rapid AL elongation in the 0.02% atropine group (βage=-0.04, P=0.01; βAL=-0.17, P=0.03), while younger age, lower baseline spherical equivalent refractive error (SER), and shorter baseline AL were associated with a greater increase in AL in the orthokeratology group (βage=-0.03, P=0.04; βSER=0.06, P=0.03; βAL=-0.11, P=0.009). Faster AL elongation was found in the 0.02% atropine group compared with the orthokeratology group at higher baseline SER (P=0.04, interaction test).

CONCLUSION

Within the limits of this study design, orthokeratology seems to be a better method for controlling AL elongation compared with administration of 0.02% atropine in children with higher myopia over a treatment period of 2 years.

Evaluating the Effect of Topical Atropine Use for Myopia Control on Intraocular Pressure by Using Machine Learning

Atropine is a common treatment used in children with myopia. However, it probably affects intraocular pressure (IOP) under some conditions. Our research aims to analyze clinical data by using machine learning models to evaluate the effect of 19 important factors on intraocular pressure (IOP) in children with myopia treated with topical atropine. The data is collected on 1545 eyes with spherical equivalent (SE) less than -10.0 diopters (D) treated with atropine for myopia control. Four machine learning models, namely multivariate adaptive regression splines (MARS), classification and regression tree (CART), random forest (RF), and eXtreme gradient boosting (XGBoost), were used. Linear regression (LR) was used for benchmarking. The 10-fold cross-validation method was used to estimate the performance of the five methods. The main outcome measure is that the 19 important factors associated with atropine use that may affect IOP are evaluated using machine learning models. Endpoint IOP at the last visit was set as the target variable. The results show that the top five significant variables, including baseline IOP, recruitment duration, age, total duration and previous cumulative dosage, were identified as most significant for evaluating the effect of atropine use for treating myopia on IOP. We can conclude that the use of machine learning methods to evaluate factors that affect IOP in children with myopia treated with topical atropine is promising. XGBoost is the best predictive model, and baseline IOP is the most accurate predictive factor for endpoint IOP among all machine learning approaches.

Selected Aspects of Ocular Toxicity Studies With a Focus on High-Quality Pathology Reports: A Pathology/Toxicology Consultant's Perspective

Ocular toxicity studies are the bedrock of nonclinical ocular drug and drug-device development, and there has been an evolution in experience, technologies, and challenges to address that ensures safe clinical trials and marketing authorization. The expectations of a well-designed ocular toxicity study and the generation of a coherent, integrative ocular toxicology report and subreports are high, and this article provides a pathology/toxicology consultant's perspective on achieving that goal. The first objective is to cover selected aspects of study designs for ocular toxicity studies including considerations for contract research organization selection, minipig species selection, unilateral versus bilateral dosing, and in-life parameters based on fit-for-purpose study objectives. The main objective is a focus on a high-quality ocular pathology report that includes ocular histology procedures to meet regulatory expectations and a report narrative and tables that correlate microscopic findings with key ophthalmic findings and presents a clear interpretation of test article-, vehicle-, and procedure-related ocular and extraocular findings with identification of adversity and a pathology peer review. The last objective covers considerations for a high-quality ophthalmology report, which in concert with a high-quality pathology report, will pave the way for a best quality toxicology report for an ocular toxicity study.

Stability of Ophthalmic Atropine Solutions for Child Myopia Control

Myopia is an ophthalmic condition affecting more than 1/5th of the world population, especially children. Low-dose atropine eyedrops have been shown to limit myopia evolution during treatment. However, there are currently no commercial industrial forms available and there is little data published concerning the stability of medications prepared by compounding pharmacies. The objective of this study was to evaluate the stability of two 0.1 mg/mL atropine formulations (with and without antimicrobiobial preservatives) for 6 months in two different low-density polyethylene (LDPE) multidose eyedroppers. Analyses used were the following: visual inspection, turbidity, chromaticity measurements, osmolality and pH measurements, atropine quantification by a stability-indicating liquid chromatography method, breakdown product research, and sterility assay. In an in-use study, atropine quantification was also performed on the drops emitted from the multidose eyedroppers. All tested parameters remained stable during the 6 months period, with atropine concentrations above 94.7% of initial concentration. A breakdown product (tropic acid) did increase slowly over time but remained well below usually admitted concentrations. Atropine concentrations remained stable during the in-use study. Both formulations of 0.1 mg/mL of atropine (with and without antimicrobial preservative) were proved to be physicochemically stable for 6 months at 25 °C when stored in LDPE bottles, with an identical microbial shelf-life.

Sustained-release voriconazole-thermogel for subconjunctival injection in horses: ocular toxicity and in-vivo studies

Background

Keratomycosis is a relatively common, sight threatening condition in horses, where treatment is often prolonged and costly. Subconjunctival (SCo) injections offer less resistance to drug diffusion than the topical route, resulting in better penetration to the ocular anterior segment. Voriconazole, a second generation triazole antifungal, is effective against common fungal organisms causing keratomycosis. If combined with a thermogel biomaterial, voriconazole can be easily injected in the SCo space to provide sustained drug release. The purpose of this study was to evaluate the drug concentrations in the anterior segment and clinical effects after SCo injections of voriconazole-containing thermogel: poly (DL-lactide-co-glycolide-b-ethylene glycol-b-DL-lactide-co-glycolide) (PLGA-PEG-PLGA) in healthy equine eyes.

Results

Voriconazole aqueous humor (AH) and tear concentrations were compared between 6 horses, receiving 1% voriconazole applied topically (0.2 mL, q4h) (Vori-Top) or 1.7% voriconazole-thermogel (0.3 mL) injected SCo (Vori-Gel). For the Vori-Gel group, voriconazole concentrations were measured in AH and tears at day 2 and then weekly for 23 days, and at day 2 only for the Vori-Top group. Ocular inflammation was assessed weekly (Vori-Gel) using the modified Hackett-McDonald scoring system. Ocular tissue concentrations of voriconazole following SCo 1.7% voriconazole-thermogel (0.3 mL) injections were evaluated post euthanasia in 6 additional horses at 3 different time points. Three horses received bilateral injections at 2 h (n = 3, right eye (OD)) and 48 h (n = 3, left eye (OS)) prior to euthanasia, and 3 horses were injected unilaterally (OS), 7 days prior to euthanasia. Voriconazole-thermogel was easily injected and well tolerated in all cases, with no major adverse effects. On day 2, drug concentrations in tears were higher in the Vori-Top, but not statistically different from Vori-Gel groups. For the Vori-Gel group, voriconazole was non-quantifiable in the AH at any time point. Total voriconazole concentrations in the cornea were above 0.5 μg/g (the target minimum inhibitory concentration (MIC) for Aspergillus sp.) for up to 48 h; however, concentrations were below this MIC at 7 days post treatment.

Conclusions

Voriconazole-thermogel was easily and safely administered to horses, and provided 48 h of sustained release of voriconazole into the cornea. This drug delivery system warrants further clinical evaluation.

Effects of Monocular Atropinization on Refractive Error and Eye Growth in Infant New World Monkeys

Purpose

To explore the effect of topical atropine on axial eye growth and emmetropization in infant marmosets.

Methods

Atropine was applied to one eye from the age of 7 to 56 days in two dose regimens, High (0.1-1% twice daily, increasing with age) or moderate (Mod) (0.1% once daily). Both eyes of the marmosets were refracted, and axial dimensions were measured ultrasonically, at 14, 28, 42, 49, 56, 70, 105, 168, and 279 days of age. The time course of each measured variable was analyzed using multilevel mixed-effects modeling realized in R.

Results

The logistic growth curves fitted to anterior segment depth (ASD) did not differ significantly between the dose regimens, but xmid, the age at which growth was half-maximal, and scal, the time constant of the exponential term in the logistic growth curve equation, differed significantly between the ASD of atropinized and untreated eyes (P = 0.03 and P < 0.0001, respectively), with the ASD of atropinized eyes shorter than that of untreated eyes. The splines fitted to lens thickness did not vary significantly with dose, but differed significantly (P < 0.0001) between the atropinized and untreated eyes, with the atropinized lenses thicker. Vitreous chamber depth (VCD) was not significantly different, but the variance of VCD was significantly greater (P < 0.001) in the atropinized compared with the untreated eyes. Refractive error (RE) became relatively myopic in atropinized eyes. The variance of RE in atropinized eyes was significantly greater (P < 0.0001) than in untreated eyes.

Conclusions

Atropine caused the infant marmoset lens to move forward and thicken, a relative myopia, and increases in the between-animals variance in VCD, which could be considered a failure of emmetropization.

Distribution of Small Molecular Weight Drugs into the Porcine Lens: Studies on Imaging Mass Spectrometry, Partition Coefficients, and Implications in Ocular Pharmacokinetics

Lens is the avascular tissue in the eye between the aqueous humor and vitreous. Drug binding to the lens might affect ocular pharmacokinetics, and the binding may also have a pharmacological role in drug-induced cataract and cataract treatment. Drug distribution in the lens has been studied in vitro with many compounds; however, the experimental methods vary, no detailed information on distribution between the lens sublayers exist, and the partition coefficients are reported rarely. Therefore, our objectives were to clarify drug localization in the lens layers and establish partition coefficients for a wide range of molecules. Furthermore, we aimed to illustrate the effect of lenticular drug binding on overall ocular drug pharmacokinetics. We studied the distribution of 16 drugs and three fluorescent dyes in whole porcine lenses in vitro with imaging mass spectrometry and fluorescence microscopy techniques. Furthermore, we determined lens/buffer partition coefficients with the same experimental setup for 28 drugs with mass spectrometry. Finally, the effect of lenticular binding of drugs on aqueous humor drug exposure was explored with pharmacokinetic simulations. After 4 h, the drugs and the dyes distributed only to the outermost lens layers (capsule and cortex). The lens/buffer partition coefficients for the drugs were low, ranging from 0.05 to 0.8. On the basis of the pharmacokinetic simulations, a high lens-aqueous humor partition coefficient increases drug exposure in the lens but does not significantly alter the pharmacokinetics in the aqueous humor. To conclude, the lens seems to act mainly as a physical barrier for drug distribution in the eye, and drug binding to the lens affects mainly the drug pharmacokinetics in the lens.