Dexamethasone concentration in the subretinal fluid after a subconjunctival injection, a peribulbar injection, or an oral dose

Periocular routes for retinal drug delivery

Despite numerous scientific efforts, delivery of therapeutic amounts of a drug to the retina remains a challenge. This challenge is compounded if chronic therapy is desired. The inability or inefficiency of topical and systemic routes for retinal delivery of existing drugs is now widely accepted. Although the intravitreal route offers high local concentrations in the vitreous and, hence, retina, these advantages are offset by side effects, such as cataracts, endophthalmitis and retinal detachment, following repeated intravitreal injections, or intravitreal placement of sustained-release implants. As discussed in this review, periocular routes, including subconjunctival, sub-tenon, retrobulbar, peribulbar and posterior juxtascleral routes, potentially offer a more promising alternative for enhanced drug delivery to the retina compared with topical and systemic routes. Periocular routes exploit the permeability of sclera for retinal drug delivery, and they are particularly useful for administering sustained-release systems of potent drugs. This review discusses the various periocular routes with respect to their anatomical location, pharmacokinetics, safety and mechanisms of drug delivery. In the coming years, several innovations in absorption enhancement, drug delivery systems and drug administration devices are anticipated for improving retinal drug delivery via periocular routes.

LIDOCAINE GEL ANESTHESIA FOR INTRAVITREAL DRUG ADMINISTRATION

PURPOSE

To describe the use of topical gel anesthesia for intravitreal injection drug delivery.

METHODS

The first group (n=12) of patients is a crossover group of patients who on separate occasions received intravitreal injections after both 2% lidocaine subconjunctival injection (SC) and 2% lidocaine topical gel anesthesia using 30-gauge needle. The second group (n=16) is a consecutive group of patients who received either SC (n=8) or gel (n=8) anesthesia before intravitreal injection of triamcinolone using 27.5-gauge needle. Descriptive and numerical pain analog scale was used to assess pain sensation.

RESULTS

: There was no difference in pain score between gel and SC within the first group (P=0.67, paired, nonparametric test) and no difference in pain score comparing patients who had either SC or gel anesthesia before 27.5-gauge intravitreal injections (P=0.82, unpaired t-test) in the second group. However, there were significant differences in incidence of chemosis (P<0.001) and subconjunctival hemorrhage (P<0.001) after injection versus gel anesthesia in both groups.

CONCLUSION

Anesthesia with lidocaine 2% gel provides satisfactory patient comfort for administration of intravitreal injection and causes less chemosis and hemorrhage than SC anesthesia.

EFFECTIVE TRANSSCLERAL DELIVERY OF TWO RETINAL ANTI-ANGIOGENIC MOLECULES

PURPOSE

To evaluate the human transscleral diffusion and intravitreal delivery of carboxyamido-triazole (CAI) and 2-Methoxyestradiol (2ME2).

METHODS

The transscleral diffusion of two retinal antiangiogenic molecules, CAI and 2ME2, was measured in vitro to assess their potential transscleral delivery. Varying concentrations and different solvents of CAI and 2ME2 were placed in the upper compartment of a two-chamber acrylic perfusion apparatus, on the episcleral side of the sclera obtained from human donor eyes. Samples were taken from the lower compartment (uveal side) for up to 24 hours and measured by high performance liquid chromatography.

RESULTS

All three solutions that contained CAI efficiently diffused through the sclera with permeability constants that ranged from 2.8 to 5.5 x 10 cm/s. The scleral permeability constant derived for 2ME2 was 9.96 x 10 cm/s. The permeability constants obtained for both CAI and 2ME2 are similar to each other as well as to permeability constants measured for other small molecules such as fluorescein and dexamethasone fluorescein.

CONCLUSION

Both CAI and 2ME2 traverse the sclera efficiently. These data combined with the reported inhibition of posterior segment neovascularization observed with these two molecules demonstrates that CAI and 2ME2 are good candidate molecules to treat posterior segment neovascularization by local delivery.

Transcorneal and transscleral iontophoresis of dexamethasone phosphate using drug loaded hydrogel

PURPOSE

To evaluate dexamethasone penetration to the eye after a short transcorneal and transscleral iontophoresis using a drug loaded hydrogel assembled on a portable iontophoretic device.

METHODS

Iontophoresis of dexamethasone phosphate was studied in healthy rabbits using drug loaded disposable HEMA hydrogel sponges and portable iontophoretic device. Corneal iontophoretic administration was performed with a current intensity of 1 mA for 1 and 4 min. Transconjunctival and transscleral iontophoresis were performed twice for 2 min at two near places in the pars-plana area, on the conjunctival membrane or directly on the sclera. Dexamethasone concentrations were assayed using HPLC.

RESULTS

Dexamethasone levels in the rabbit cornea after a single transcorneal iontophoresis for 1 min were up to 30 fold higher compared to those obtained after frequent eye drop instillation. Also, high drug concentrations were obtained in the retina and sclera 4 h after transscleral iontophoresis.

CONCLUSIONS

A short low current non-invasive iontophoretic treatment using dexamethasone-loaded hydrogels has potential clinical value in increasing drug penetration to the anterior and posterior segments of the eye.

SUPPRESSION OF LASER-INDUCED CHOROIDAL NEOVASCULARIZATION BY POSTERIOR SUB-TENON ADMINISTRATION OF TRIAMCINOLONE ACETONIDE

PURPOSE

To evaluate the inhibitory effect of triamcinolone acetonide (TA) on choroidal neovascularization (CNV) by posterior sub-Tenon administration using a laser-induced CNV model in the rat.

METHODS

Experimental CNV was induced by laser photocoagulation in Brown-Norway male rats. Experimental eyes received posterior sub-Tenon administration of either 2 mg (n = 10) or 0.5 mg (n = 8) of TA. Control eyes (n = 10) received posterior sub-Tenon administration of isotonic sodium chloride solution. Two weeks after treatment, CNV was evaluated by fluorescein angiography and histopathological examination. Concentrations of TA in the vitreous, retina, and choroid were determined by high-performance liquid chromatography at 3 and 7 days after posterior sub-Tenon administration.

RESULTS

The eyes treated with 2 mg of TA showed statistically significant inhibition of fluorescein leakage by fluorescein angiography, as compared with control eyes and eyes treated with 0.5 mg of TA (P < 0.01). The thickness of CNV membranes in eyes treated with 2 mg of TA also decreased statistically significantly, as compared with control eyes (P < 0.01). TA was detected in the vitreous, retina, and choroid 3 days after administration and in the choroid 7 days after administration.

CONCLUSIONS

Posterior sub-Tenon administration of TA may be useful to treat CNV.

Periocular corticosteroids in diabetic papillopathy

PURPOSE

To ascertain the therapeutic effect of periocular corticosteroids in diabetic papillopathy.

METHODS

Prospectively, five consecutive adult-onset diabetic patients with symptomatic diabetic papillopathy underwent visual fields and fluorescein angiography before and after superonasal subtenon injection of corticosteroids.

RESULTS

The median duration of papillopathy was 2.5 weeks by ophthalmoscopy and 3 weeks by fluorescein angiography. The median recovery time of best-spectacle-corrected visual acuity was 2 weeks. Two patients developed sequential diabetic papillopathy, and both reported faster visual recovery and better subjective vision in treated eyes. In these two patients, the final best-spectacle-corrected visual acuity and visual evoked responses were comparable between the two eyes, while automated visual fields were less constricted in treated eyes. Complications included ocular hypertension, mild progression of cataract, and mild ptosis in one patient each.

CONCLUSIONS

Periocular corticosteroids shortened the duration of diabetic papillopathy from a reported median of 5 months to 3 weeks in the present uncontrolled observational study, partly by their angiostatic and antioedema effects at the level of the anterior optic nerve. Intraocular pressure needs to be monitored in eyes receiving periocular corticosteroids.

Retinal delivery of celecoxib is several-fold higher following subconjunctival administration compared to systemic administration

PURPOSE

We have previously demonstrated that celecoxib, a selective COX-2 inhibitor, reaches the retina following repeated oral administrations and inhibits diabetes-induced vascular endothelial growth factor (VEGF) mRNA expression and vascular leakage in a rat model. The aim of this study was to quantify the relative retinal bioavailability of celecoxib from the subconjunctival route compared to a systemic route.

METHODS

The plasma and ocular tissue distribution of celecoxib was determined in male Sprague-Dawley rats following subconjunctival and intraperitoneal administrations of drug suspension at a dose of 3 mg/rat. The animals were sacrificed at 0.5, 1, 2, 3, 4, 8, and 12 h post-dosing, the blood was collected, and the eyes were enucleated and frozen. The plasma, sclera, retina, vitreous, lens, and the cornea were isolated and celecoxib levels were determined using an HPLC method. The tissue exposure of the drug was measured as the area under the curve (AUC(0-infinity)) of the concentration vs. time profiles. The relative bioavailability was estimated as the AUC(0-infinity) ratio between subconjunctival and intraperitoneal groups.

RESULTS

For the subconjunctivally dosed (ipsilateral) eye, the AUC(0-infinity) ratios between subconjunctival and intraperitoneal groups were 0.8 +/- 0.1, 53 +/- 4, 54 +/- 8, 145 +/- 21, 61 +/- 16, and 52 +/- 6 for plasma, sclera, retina, vitreous, lens, and cornea, respectively. For the contralateral ocular tissues, the AUC0-infinity ratios were 1.2 +/- 03, 11 +/- 0.3, 1.1 +/- 0.4, 1.0 +/- 0.3, and 1.2 +/- 0.3 in the sclera, retina, vitreous, lens, and the cornea, respectively, between the subconjunctival and the intraperitoneal groups. Assuming that the drug AUCs in contralateral eye were equal to the systemic pathway contribution to AUCs in the ipsilateral eye, the percent contribution of local pathways as opposed to systemic circulation for celecoxib delivery to the ipsilateral eye tissues was estimated to be 98% or greater.

CONCLUSIONS

The retinal delivery of celecoxib was substantially higher following subconjunctival administration compared to the intraperitoneal route. The transscleral pathway almost completely accounts for the retinal celecoxib delivery following subconjunctival administration.

In vitro human scleral permeability of fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein and rhodamine 6G and the use of a coated coil as a new drug delivery system

PURPOSE

To determine the in vitro human scleral permeability of several dyes and drugdye combinations with varying molecular weights (MW) and lipid solubilities (fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein, and rhodamine). Coils coated with rhodamine were also evaluated for scleral permeability and sustained release.

METHODS

Scleral sections excised from moist chamber stored human globes were mounted in a 2-compartment perfusion chamber. A small depot of drug/dye (100 microl of 10(-4) M fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein or rhodamine) or a coated coil in 100 microl of BSS was added to the episcleral surface while perfusing BSS to the choroidal side. The perfusate was collected and measured for fluorescence. Permeability was calculated as Ktrans from the flux measurements.

RESULTS

Ktrans values (cm/sec, mean +/- SE) for the studied dyes and drug-dye combinations were 5.21 +/- 0.71 x 10(-6) for fluorescein, 1.64 +/- 0.17 x 10(-6) for dexamethasone-fluorescein, 3.36 +/- 0.62 x 10(-6) for methotrexate-fluorescein, 1.86 +/- 0.39 x 10(-6) for rhodamine and 2.18 +/- 0.23 x 10(-6) for the rhodamine from the coils. We found a significant difference between the permeability of the sclera to fluorescein and dexamethasone-fluorescein (P < 0.001), methotrexate-fluorescein (P < 0.05) and rhodamine (P < 0.001). Steady state flux was observed from the rhodamine coil.

CONCLUSION

The rank order of scleral permeability to the studied dyes is as follows: fluorescein > methotrexate-fluorescein > rhodamine coil > rhodamine 6G > dexamethasone-fluorescein. Differences in scleral permeability are related to MW and lipid solubility. Prolonged transscleral diffusion of rhodamine delivered by solution and by coil are similar.

Locally administered ocular corticosteroids: benefits and risks

Corticosteroids, used prudently, are one of the most potent and effective modalities available in the treatment of ocular inflammation. However, they can produce a plethora of adverse ocular and systemic events. In order to optimise and target drug delivery, whilst minimising systemic adverse effects, a diverse range of local ophthalmic preparations and delivery techniques have been developed. Topical drops and ointments remain the primary methods for administration of ocular corticosteroids. However, ocular penetration of topical corticosteroid drops depends upon drug concentration, chemical formulation of corticosteroid, and composition of the vehicle, therefore, apparently small modifications in preparations can produce a more than 20-fold difference in intraocular drug concentration. Periocular injections of corticosteroids continue to have a useful, but limited, therapeutic role and longer acting, intraocular delayed-release devices are in early clinical studies. Although newer corticosteroids with lesser pressure elevating characteristics have been developed, corticosteroid-induced ocular hypertension and glaucoma continue to be significant risks of local and systemic administration. Posterior subcapsular cataract, observed following as little as 4 months topical corticosteroids use, is thought to be due to covalent binding of corticosteroid to lens protein with subsequent oxidation. Inappropriate use of topical corticosteroid in the presence of corneal infections also continues to be a cause of ocular morbidity. Other risks of locally administered ophthalmic corticosteroids include: tear-film instability, epithelial toxicity, crystalline keratopathy, decreased wound strength, orbital fat atrophy, ptosis, limitation of ocular movement, inadvertent intraocular injection, and reduction in endogenous cortisol. This extensive review assesses the therapeutic benefits of locally administered ocular corticosteroids in the context of the risks of adverse effects.