Intraocular penetration and systemic absorption after topical application of dexamethasone disodium phosphate

PURPOSE: To study the dexamethasone concentration in aqueous humor, vitreous, and serum of patients after repeated topical application of dexamethasone disodium phosphate. DESIGN: Prospective nonrandomized comparative trial. PARTICIPANTS: Twenty phakic patients scheduled for a first vitrectomy. METHODS: All participants received dexamethasone disodium phosphate drops according to an application schedule intended to result in steady-state drug concentrations. Starting on the preoperative day, they received 1 drop of dexamethasone disodium phosphate (0.1%) every 1 hours until the time of vitrectomy (total, 10 or 11 drops). At night, ointment containing dexamethasone (0.3 mg/g) and gentamicin (5 mg/g) was administered once. From 7 AM on, the drop application schedule was resumed. At the start of the vitrectomy, samples were taken from the aqueous humor, vitreous, and blood. MAIN OUTCOME MEASURES: The dexamethasone concentrations in the aqueous humor, vitreous, and serum measured by radioimmunoassay. RESULTS: The mean dexamethasone concentrations in the aqueous humor, vitreous, and serum were 30.5 ng/ml (range, 7.1-57.7; standard deviation [SD] 15.0), 1.1 ng/ml (range, 0.0-1.6; SD 0.4), and 0.7 ng/ml (range, 0.0-1.2; SD 0.4), respectively. CONCLUSIONS: Compared with previously tested administration routes (peribulbar or subconjunctival injection or oral administration), the penetration of dexamethasone into the vitreous after repeated drop application is negligible. Despite the frequent dosing schedule, the dexamethasone concentration in the aqueous humor is far lower than after a subconjunctival injection with dexamethasone disodium phosphate. Systemic uptake is low.     

地塞米松-PLGA纳米粒兔眼玻璃体内注射的药物代谢动力学

目的地塞米松(dexamethasone,DM)是眼科临床常用药物,但目前缺乏高效、低毒的给药途径。借助生物降解性多聚体材料聚乳酸-羟乙酸(PLGA)构建DM-PLGA纳米粒,兔眼玻璃体内注射可望在眼后节较长时间维持稳定的有效药物浓度。方法乳化/溶剂蒸发法制备载药量分别为20%和50%的DM-PLGA纳米粒,兔眼玻璃体内注射给药后于第1、7、14和21d分别进行临床观察和组织药物浓度的高效液相色谱分析。结果给药后21d内,角膜和房水中药物浓度均低于检测水平下限(10μg·L-1);血浆药物浓度最高为024mg·L-1;载药量20%和50%的2组中视网膜脉络膜药物浓度分别为011-0.42mg·L-1和0.38-0.88mg·L-1,玻璃体药物浓度分别为0.82-26.52mg·L-1和1.78-85.72mg·L-1。临床观察眼底未见异常。结论载药量50%组的DM-PLGA纳米粒在兔眼玻璃体内可维持药物浓度达3周,提示具有眼内注射应用的潜力。     

Comparison of topical and subconjunctival anesthesia in intravitreal injection administrations

PURPOSE: To compare the effectiveness of topical and subconjunctival anesthesia in intravitreal injection administrations. METHODS: Twenty-eight patients from a university clinic with bilateral diabetic macular edema were prospectively randomized to receive intravitreal injection of 4 mg triamcinolone under topical anesthesia for one eye and subconjunctival anesthesia for the other eye by using lidocaine 4%. Patients were asked to grade the pain they experienced during administration of both anesthesia and intravitreal injection by using a 4-point pain scale: from 0=no pain to 3=severe pain. Complications that developed during both procedures were recorded. RESULTS: The mean pain score experienced during subconjunctival injections was 0.78+/-0.62, whereas no anesthesia-related pain was reported in the topical group. The mean pain score experienced during intravitreal injection was 1.64+/-0.67 in the topical and 0.85+/-0.52 in the subconjunctival group (p<0.001). The mean total pain scores of both procedures were 0.82+/-0.34 in the topical and 0.82+/-0.51 in the subconjunctival group (p>0.05). Nine eyes (32%) developed subconjunctival haemorrhage after subconjunctival injection, whereas no anesthesia-related complication developed in the topical group. Subconjunctival haemorrhage was also observed in 5 eyes (18%) in the topical group and in 11 eyes (40%) in the subconjunctival group (p>0.05) after intravitreal injection. CONCLUSIONS: Although subconjunctival anesthesia provides better pain control during intravitreal injections, its application is more painful and leads to subconjunctival haemorrhage. Moreover, the mean total pain scores are similar in both methods. Therefore, topical anesthesia may be more suitable for daily practice.     

High concentration of dexamethasone in aqueous and vitreous after subconjunctival injection.

PURPOSE: To determine the dexamethasone concentration in aqueous, vitreous, and serum of patients after a subconjunctival injection with dexamethasone disodium phosphate and to compare the effectiveness of a subconjunctival injection as a method of delivering dexamethasone into the vitreous with that of two previously tested routes: peribulbar injection and oral administration. METHODS: In a prospective study, 50 phakic patients who underwent a pars plana vitrectomy received a single subconjunctival injection with 2.5 mg of dexamethasone disodium phosphate, aqueous solution (after topical anesthesia and a subconjunctival injection with lidocaine) at varied intervals before surgery. An aqueous and a vitreous sample were taken from each patient, and serum samples were collected at multiple time points from nine of 50 patients. Dexamethasone concentrations were measured by radioimmunoassay. RESULTS: The estimated maximum dexamethasone concentration in the aqueous was 858 ng per ml at 2.5 hours after injection, and in the vitreous, 72.5 ng per ml at 3 hours. In serum, a mean maximum concentration of 32.4 ng per ml was measured at approximately 30 minutes after injection. CONCLUSIONS: Subconjunctival injection of 2.5 mg of dexamethasone disodium phosphate resulted in an estimated vitreous dexamethasone peak concentration three and 12 times higher, respectively, than after a peribulbar injection of 5 mg of dexamethasone disodium phosphate and an oral dose of 7.5 mg of dexamethasone. Thus, a subconjunctival injection is the most effective method of delivering dexamethasone into both the anterior and posterior segments of the eye. Systemic drug absorption is considerable and is of the same order of magnitude as after peribulbar injection.     

磁共振成像对活体兔结膜下药物注射后渗透性的评价作用

目的使用磁共振成像（magnetic resonance imag-ing,MRI）评价兔结膜下药物注射后的渗透性和清除率,探讨一种能够在活体内动态观察的眼部药代动力学检测方法。方法健康新西兰白兔24只,按随机数字表法分为3组,每组8只,取右眼作为实验眼,对侧眼作为对照眼。以MRI的造影剂钆喷酸葡胺（Gadolinium-diethylene triamine pentaaceticacids,Gd-DTPA）作为示踪剂,分别于结膜下注射0.5mol/L、0.05mol/L、0.005mol/L造影剂0.1ml,对照眼注射0.9%生理盐水0.1ml。采用MRI扫描仪,于注药后1h内每间隔15min左右扫描1次,2～3h内间隔30min左右扫描1次,通过MRI观察药物的渗透性、眼内分布及结膜下的清除速度。0.5mol/L组于术前和术后24h进行角膜内皮镜检查,观察角膜内皮细胞密度、内皮细胞面积变异系数、六边形细胞百分数和中央角膜厚度。使用Excel绘制信号增强率对时间曲线,采用配对t检验分析角膜内皮细胞密度变化。结果MRI扫描可见：0.5mol/L组前房及睫状体信号明显增强,而眼后段则未探测到高信号;0.05mol/L组前房信号无明显增强,接近注射位置的睫状体信号增强;0.005mol/L组眼前、后段的药物渗透浓度均低于MRI探测阈值。睫状体部位对药物经巩膜的被动转运阻力最低,结膜下药物的体积和浓度随时间逐渐下降。结膜下Gd-DTPA用药前后,0.5mol/L组的角膜内皮细胞密度、内皮细胞面积变异系数、六边形细胞百分数和中央角膜厚度差异均无统计学意义（P〉0.05）。结论MRI作为非侵袭、动态、实时的检查方法可于活体内定量分析结膜下药物注射后的渗透效率,是对传统药代动力学研究方法的有力补充。     

Experimental intravitreal application of trovafloxacin in rabbits.

This study was performed to examine the retinal toxicity of trovafloxacin, a broad-spectrum fourth-generation fluoroquinolone, in rabbit eyes after intravitreal injection. The left eyes of 20 albino rabbits were divided into four groups, and each was injected intravitreally with 0.1 ml of trovafloxacin in a 50-microg, 100-microg, 250-microg or 500-microg concentration. The right eyes of these rabbits served as control and received normal saline solution. Retinal function was assessed from the electroretinogram (ERG), and retinal structure was also examined by ophthalmoscopy and histologic study (light microscopy). The intravitreal injections of 50 microg, 100 microg, and 250 microg trovafloxacin did not significantly change the ERG a-wave, b-wave or the oscillatory potential throughout the follow-up period of 4 weeks. While no ERG changes were observed at 4 weeks after injection, in the 3 eyes that received trovaloxacin 500 microg/0.1 ml, the a-wave amplitudes showed a diminution of 56-49% and those of b-waves one of 53-44% of the preinjection amplitudes at 4 weeks after injection, but oscillatory potentials remained unchanged in the other 2 rabbits intravitreally injected with 500 microg trovafloxacin. However, in none of the injected eyes and the control eyes in all groups were ophthalmoscopically visible fundus changes and histologic abnormality observed. The results suggest that intravitreally injected trovafloxacin at a dose of up to 500 microg is nontoxic to the rabbit retina. If future studies in other species confirm our findings, intravitreal trovafloxacin may be a good alternative in the treatment and prevention of clinical bacterial endophthalmitis.     

Evaluation of a single intravitreal injection of dexamethasone phosphate in vitrectomy surgery for diabetic retinopathy complications

For evaluation of the efficacy and toxicity of dexamethasone phosphate after pars plana vitrectomy, 27 randomly selected eyes received 0.8 mg intravitreal dexamethasone phosphate and 30 control eyes did not receive this injection. No signs of dexamethasone phosphate toxicity were observed during 6 months of followup evaluations. Visual acuities of 20/40 or better were obtained in 26% of the dexamethasone-treated group and 33% of the control group, and those of 20/200 or better were obtained in 74% of the dexamethasone-treated eyes and 73% of the control eyes. Moderate anterior chamber flare or fibrin formation occurred in only 15% of the dexamethasone-treated eyes but in 27% of the control eyes one day after surgery. Lens changes occurred equally in both groups. None of the eyes in either group developed substantial intraocular proliferation or membranes following surgery.This project was supported in part by patients and contributors of the Departments of Ophthalmology, University of Miami School of Medicine and Penn State University College of Medicine; Research to Prevent Blindness, Inc., New York City; Pennsylvania Lions Vision and Research Center; and the Breen Green Diabetic Retinopathy Fund, Miami, Florida     

Pharmacokinetic and toxicity investigations of a new intraocular lens with a dexamethasone drug delivery system: a pilot study

AIM: To investigate the short-term safety and pharmacokinetic behavior of a new intraocular lens containing a dexamethasone drug delivery system (IOL-DDS) in rabbit eyes. METHODS: A modified polymethylmethacrylate IOL containing a biodegradable dexamethasone DDS was implanted into the posterior chamber of the right eyes of 9 New Zealand white rabbits. Serial slitlamp and indirect ophthalmoscopic examinations (including grading of intraocular inflammation) were performed. After 3, 6 and 9 days, the rabbits were euthanized and the globes were removed for histological examination and for determination of dexamethasone levels in the aqueous humor and in the vitreous. Analysis of dexamethasone concentrations was performed by ELISA. RESULTS: Therapeutic concentrations of dexamethasone were detectable in the aqueous and vitreous of the study eyes throughout the 9-day period in all tested animals. The mean aqueous dexamethasone concentration (ng/ml, +/- SD) was 1,015.42 (+/- 43.05), 970.11 (+/- 32.47) and 757.58 (+/- 30.19) and the mean vitreous concentration (ng/ml, +/- SD) was 399.82 (+/- 38.05), 287.38 (+/-34.47) and 268.15 (+/- 32.00) at 3, 6 and 9 days after the surgical procedure, respectively. No corneal or retinal histological changes were observed during the study period. CONCLUSION: The IOL-DDS is effective in delivering therapeutic concentrations of dexamethasone to the aqueous and vitreous, without acute damage to the cornea and retina. Further controlled studies in the same animal model are under way to determine the potential value of this lens in the prevention and treatment of inflammation following cataract surgery.     

A study on the toxicity of intravitreal levofloxacin in rabbits

PURPOSE: To investigate the retinal toxicity of different doses of intravitreal injections of levofloxacin in a rabbit model, which is the levorotatory component of ofloxacin and approximately twice as potent as ofloxacin and highly active in vitro against gram-positive and -negative bacteria, and anaerobic bacteria including many ocular pathogens. METHODS: Sixteen albino rabbits were used in this study, and divided four groups. Levofloxacin in doses of 50, 100, 250 and 500 microg was injected into the midvitreous of rabbit's left eyes. The other eye served as a control and received normal saline solution. Indirect ophthalmoscopy, electroretinography (ERG) and light microscopy were used for retinal toxicity of levofloxacin. ERGs were recorded before injection and at 1(st) day, 1(st), 2(nd) and 4(th) weeks. At the end of follow-up period, the rabbits were killed and the eyes were enucleated for histologic evaluation. RESULTS: Intravitreal injections of 50, 100, 250 and 500 microg levofloxacin did not cause any deterioration of the a-wave, b-wave or oscillatory potentials of ERG throughout the follow-up period of 4 weeks. No evidence of retinal toxicity was observed by indirect ophthalmoscopy and light microscopy in any case. CONCLUSIONS: In therapeutic doses of 500 microg or less, intravitreal levofloxacin does not have retinal toxicity in rabbit eyes and this dose was well above the MIC(90) values of ocular pathogens that cause endophthalmitis. If future studies in other species confirm our findings, intravitreal levofloxacin may be a potentially important drug in the treatment and prevention of clinical bacterial endophthalmitis.     

The efficacy of intravitreal levofloxacin and intravitreal dexamethasone in experimental Staphylococcus epidermidis endophthalmitis

This study was designed to investigate the efficacy of intravitreal levofloxacin, and intravitreal levofloxacin and dexamethasone combined in Staphylococcus epidermidis endophthalmitis. Albino rabbits (n = 25), infected with an intravitreal inoculum of S. epidermidis (1.0 x 10(5) colony forming units/0.1 ml), were divided into five groups (n = 5). Groups 1 and 2 received treatment 24 h after the inoculation, and groups 3 and 4 48 h after the inoculation. No treatment was given to the control group. Treatment efficacy was assessed by vitreous culture, clinical examination and histopathology. Five days after treatment, groups 1 and 2 had significantly lower clinical scores than the control group (p = 0.004, p = 0.007). The culture results of the treatment groups were sterile. The histopathological scores of the treatment groups were lower than the control group (p = 0.007). Studies on retinal toxicity and dose-response relation are needed to prove the efficacy of levofloxacin in S. epidermidis endophthalmitis.     

The intravitreal penetration of cefotaxime in man following systemic and subconjunctival administrations

Of 30 patients scheduled to undergo elective vitreal surgery, five received a single dose of 1000 mg of cefotaxime intramuscularly and 25 received 100 mg subconjuctivally. Specimens of serum and vitreous were collected from 30 minutes to five hours after drug administration, and were assayed for cetotaxime concentration by bioassay and high pressure liquid chromatography. In the five patients who received the intramuscular dose, no cefotaxime or its major metabolite could be detected in the vitreous. In the 25 patients who received the subconjunctival dose, cefotaxime or its metabolite could be only detected in patients with aphakia or in those who previously underwent vitreal surgery. Cefotaxime in intramuscular administration should not be relied upon as appropriate prophylaxis for vitreal surgery. Cefotaxime in subconjunctival administration reaches therapeutic levels in the vitreous only in previously operated eyes.     

Histological study of intraocular changes in rabbits after intravitreal gas injection

To study the effects of different intravitreal gases on intraocular tissues, adult pigmented rabbits were given 0.4 mL intravitreal injections of air, 50% sulfur hexafluoride (SF₆) and air, 100% SF₆, 50% perfluoropropane (C₃F₈), or 100% CA. On postinjection days 1, 4, 7, and 14, the eyes were removed and the iris, ciliary body and retina processed for light and electron microscopy. Histopathological examination found no abnormalities in eyes that received air and none in the irises of gas-injected eyes. Eyes that received 50% or 100% SF₆, or 50% C₃f₈ had vacuolar changes in the ciliary body and retina after maximum gas expansion; these changes were transient, returning to normal as the gas was absorbed. Eyes that received 100% C₃F₈ suffered irreversible damage to the ciliary body and retina, in both the superior and inferior portions. These observations indicate that expansion of some intravitreal gases can cause both reversible and irreversible changes in intraocular tissues. The degree of damage is affected by the duration of exposure and the gas concentration. Highly concentrated, long-lasting gases can cause irreversible changes resulting in breakdown of the blood-ocular barrier and impaired retinal function.     

Effects of subconjunctival injection of mitomycin-C on iridial circulation in rabbits.

PURPOSE. To determine the effects of a subconjunctival injection of mitomycin-C (MMC) on iridial circulation in rabbits. METHODS. Dutch rabbits anesthetized with pentobarbital received a 0.2-ml subconjunctival injection of 0.4 mg/ml or 0.1 mg/ml MMC; the contralateral eye received 0.2 ml physiological saline. Intraocular pressure (IOP) and NB( iris), a quantitative index of iridial tissue blood velocity, were measured up to 24 hours after treatment. RESULTS. At a dosage of 0.4 mg/ml MMC, NB iris obtained from the iridial area adjacent to the injection site decreased significantly by 13.6% and 18.6% at 1 and 2 hours (P = 0.03, 0.01, respectively) after treatment; NB iris obtained on the contralateral side of the injection showed no significant change. In eyes treated with 0.1 mg/ml MMC, NB iris did not change significantly. The mean IOP was significantly lower by 3.1, 3.0, and 1.8 mm Hg at 6, 12, and 24 hours after the 0.4 mg/ml injection of MMC compared with the fellow eyes (P = 0.03, 0.01, and 0.03, respectively), the IOP decreased by 1.7 mm Hg at 4 hours in the eyes treated with 0.1 mg/ml MMC (P = 0. 04). CONCLUSIONS. Subconjunctival injections of 0.2 ml of 0.4 mg/ ml MMC caused not only a significant decrease of IOP but also a transient but significant effect on iridial circulation.     

Safety of intravitreal triamcinolone acetonide:an electrophysiologic and histopathological study in rabbits

AIM

To evaluate the retinal safety of various doses of intravitreal triamcinolone acetonide (TA) in rabbits.

Methods

Thirty New Zealand albino rabbits were divided into five groups (six animals each). In group 1 (control group), each animal received a single intravitreal injection of 0.1mL phosphate buffered saline. In groups 2, 3, 4 and 5, each rabbit received a single intravitreal injection of 4, 8, 16 and 32mg of TA, respectively. Each dose was contained in 0.1mL phosphate buffered saline. Clinical ocular examinations were performed before the injection and on the 1st, 3rd, 10th and 17th post-injection days. A standard dark adapted electroretinogram (ERG) was obtained before injection and on the 3rd, 10th and 17th post-injection days. After 17d, animals were sacrificed and their eyes prepared for pathological examination.

RESULTS

By monitoring ERG as a functional index for the retina, intravitreal injection of 4mg TA showed no significant ERG changes. At doses of 8, 16 and 32, hyper-abnormal responses in a- and b- waves of ERG were detected on the 3rd post-injection day. These changes gradually returned back to normal limits after 17d. Histopathological examination of the retina of all animals showed no pathological changes.

CONCLUSION

High doses of intravitreal TA seemed to have enhancing effects on the retinal function with gradual return to normal limits with no pathological changes detected in examined eyes.     

Safety of intravitreal triamcinolone acetonide:an electrophysiologic and histopathological study in rabbits

AIM: To evaluate the retinal safety of various doses of intravitreal triamcinolone acetonide (TA) in rabbits.Methods: Thirty New Zealand albino rabbits were divided into five groups (six animals each). In group 1 (control group), each animal received a single intravitreal injection of 0.1mL phosphate buffered saline. In groups 2, 3, 4 and 5, each rabbit received a single intravitreal injection of 4, 8, 16 and 32mg of TA, respectively. Each dose was contained in 0.1mL phosphate buffered saline. Clinical ocular examinations were performed before the injection and on the 1st, 3rd, 10th and 17th post-injection days. A standard dark adapted electroretinogram (ERG) was obtained before injection and on the 3rd, 10th and 17th post-injection days. After 17d, animals were sacrificed and their eyes prepared for pathological examination.RESULTS:By monitoring ERG as a functional index for the retina, intravitreal injection of 4mg TA showed no significant ERG changes. At doses of 8, 16 and 32, hyper-abnormal responses in a- and b- waves of ERG were detected on the 3rd post-injection day. These changes gradually returned back to normal limits after 17d. Histopathological examination of the retina of all animals showed no pathological changes.CONCLUSION: High doses of intravitreal TA seemed to have enhancing effects on the retinal function with gradual return to normal limits with no pathological changes detected in examined eyes.     

Quantitative MR imaging study of intravitreal sustained release of VEGF in rabbits

PURPOSE: To determine whether sustained elevation of vascular endothelial growth factor (VEGF) in the vitreous cavity causes retinal hyperpermeability [blood-retinal barrier (BRB) breakdown] before the development of retinal neovascularization (NV) and to document the kinetics of the integrity of BRB breakdown versus time. METHODS: Poly(L-lactide-co-glycolide)based devices loaded with VEGF were implanted intravitreally in rabbit eyes. Contrast-enhanced magnetic resonance imaging (MRI) methods were used to identify and quantitate the retinal permeability at various time points after implantation. This was done with the newly developed MR tracer AngioMARK (Epix Medical, Boston, MA). After the MRI measurements, fundus photography and fluorescein angiography (FA) also were performed on the same set of animals. RESULTS: At 3 days after implantation, the MR images showed a significant retinal leakage into the vitreous cavity (BRB breakdown) of the VEGF-implanted eyes. To quantitate this leakage, the permeability surface area product (PS) was measured. At 3 days, the mean PS product was 1.25 +/-0.25 x 10(-5) cm3/min. Based on the VEGF in vitro release study, this 3-day BRB breakdown corresponded to a total sustained release of 7.42 +/- 0.54 microg/ml of VEGF. The fundus and FA photographs of these VEGF-implanted eyes taken at 4 days after implantation also showed a considerable level of retinal vascular dilation and tortuosity. By 12 days after implantation, the mean PS product decreased to 5.83 +/- 1.38 x 10(-6) cm3/min. However, the retinal NV was observed only after the second week after implantation. By this time, a total of 10.70 +/- 0.92 microg/ml of VEGF was released in a sustained fashion. Also, after the retinal NV development, retinal detachment also was observed. The control eyes, however, which were implanted with blank devices, remained unchanged and normal during the entire course of this study (PS = 5.57 +/- 0.66 x 10(-7) cm3/min). CONCLUSIONS. The findings indicate that sustained delivery of elevated amounts of VEGF in the vitreous cavity induces a BRB breakdown even earlier than 3 days after implantation. This was achieved after a total sustained release of 7.42 +/- 0.54 microg/ml of VEGF. This retinal leakage regressed by more than half by the time the retinal NV developed. Furthermore, a retinal detachment occurred after this retinal NV. These results are similar to proliferative diabetic retinopathy (PDR). The sustained elevation of VEGF in the vitreous cavity of rabbit eyes is potentially a good model to test VEGF antagonists to treat or prevent PDR in humans. The quantifiable change of BRB breakdown by the contrast-enhanced MRI method is ideal to assess the therapeutic intervention in vivo without killing the animal and may prove to be clinically useful in humans.