Intravitreal vancomycin and gentamicin concentrations in patients with postoperative endophthalmitis

BACKGROUND/AIMS: To study the intravitreal antibiotic concentrations and the efficacy of an intravitreal dosing regimen to treat patients with postoperative bacterial endophthalmitis. This regimen, based on pharmacokinetic/pharmacodynamic considerations, relies on a repeat antibiotic injection of a lower dose than is generally used. METHODS: In consecutive patients with suspected postoperative endophthalmitis a vitreous biopsy for bacterial culture was taken before 0.2 mg vancomycin and 0.05 mg gentamicin were injected intravitreally. After 3 or 4 days a second biopsy was taken for bacteriological culture and to measure intravitreal vancomycin and gentamicin concentrations, followed by a repeat injection of 0.2 mg vancomycin. RESULTS: 17 patients entered the study. In 11 patients the initial bacterial culture was positive, predominantly coagulase negative staphylococci. All second vitreous biopsies were sterile. Intravitreal vancomycin levels varied between 2.6 and 18.0 microg/ml (mean 10.3 (SD 4.1) microg/ml) after 3 days and between 3.1 and 16.6 microg/ml (mean 7.5 (6.2) microg/ml) after 4 days which is well above the minimal inhibitory concentration for most micro-organisms. Concentrations of intravitreal gentamicin varied between 0.90 and 3.3 microg/ml (mean 1.6 (0.72) microg/ml) after 3 days and between 1.2 and 2.6 microg/ml (mean 1.9 (0.99) microg/ml) after 4 days. CONCLUSION: This dosing regimen resulted both in adequate intravitreal vancomycin and gentamicin levels for over a week as well as in negative second cultures. This study also provides new information on intravitreal vancomycin and gentamicin concentration over time in patients with postoperative endophthalmitis.     

Effect of vitrectomy on the ocular distribution of gentamicin in the rabbit

To determine whether vitrectomy affects the ocular distribution of intravitreally injected gentamicin sulfate, 25 pigmented rabbits received an intravitreal injection of gentamicin (control group), and 25 other pigmented rabbits underwent pars plana vitrectomy followed by an intravitreal injection of gentamicin (experimental group). The animals were killed in groups of five 1, 3, 6, 12 and 24 hours after the injection. The mean retinal gentamicin levels 1 and 3 hours after the injection were significantly higher in the experimental group than in the control group (p less than 0.01). The mean gentamicin level in the aqueous humour was significantly lower in the experimental group than in the control group 1 hour (p less than 0.01), 6 hours (p less than 0.01) and 24 hours (p less than 0.001) after the injection. The mean corneal gentamicin level 24 hours after the injection was significantly lower in the experimental group than in the control group (p less than 0.05). There was no significant difference in mean choroidal gentamicin level between the two groups. We conclude that vitrectomy significantly affects the ocular distribution of gentamicin in the rabbit.     

A new method for continuous intraocular drug delivery

A novel device for the continuous intraocular delivery of drugs is described. The active intraocular component of the device is made from hollow haemodialysis fibres. During operation, the drug to be administered diffuses from a small extraocular reservoir to the intraocular fibres, where it passes through the semipermeable walls and into the vitreous body. The delivery of gentamicin by the device into the vitreous body of the cat is compared with direct intraocular injection techniques. Characteristics of the process of drug delivery were influenced by the geometry and design of the device. A reservoir concentration of 10 g/L gentamicin sulphate in a device with four fibres, each 5 mm long, resulted in stable vitreal gentamicin levels of 104 to 128 mg/L at 10 hours. Intravitreal injection of 0.1 ml of a 10 g/L solution of gentamicin caused localised peaks of intravitreal gentamicin concentration in the range 1180 to 3296 mg/L, before falling to 356 to 665 mg/L at 10 hours. The device provides the opportunity of a more controlled and continuous drug delivery, thus avoiding the high localised concentrations that may occur with direct injection techniques in which the required dose is delivered as a bolus. Refinement of a device of this type may result in a clinically useful method of intraocular drug delivery for drugs which present a risk of localised retinal toxicity or require repetitive administration with conventional intraocular injection techniques.     

A new method for continuous intraocular drug delivery

A novel device for the continuous intraocular delivery of drugs is described. The active intraocular component of the device is made from hollow haemodialysis fibres. During operation, the drug to be administered diffuses from a small extraocular reservoir to the intraocular fibres, where it passes through the semipermeable walls and into the vitreous body. The delivery of gentamicin by the device into the vitreous body of the cat is compared with direct intraocular injection techniques. Characteristics of the process of drug delivery were influenced by the geometry and design of the device. A reservoir concentration of 10 g/L gentamicin sulphate in a device with four fibres, each 5 mm long, resulted in stable vitreal gentamicin levels of 104 to 128 mg/L at 10 hours. Intravitreal injection of 0.1 ml of a 10 g/L solution of gentamicin caused localised peaks of intravitreal gentamicin concentration in the range 1180 to 3296 mg/L, before falling to 356 to 665 mg/L at 10 hours. The device provides the opportunity of a more controlled and continuous drug delivery, thus avoiding the high localised concentrations that may occur with direct injection techniques in which the required dose is delivered as a bolus. Refinement of a device of this type may result in a clinically useful method of intraocular drug delivery for drugs which present a risk of localised retinal toxicity or require repetitive administration with conventional intraocular injection techniques.     

Liposomally-entrapped ganciclovir for the treatment of cytomegalovirus retinitis in AIDS patients

Treatment of retinitis by cytomegalovirus (CMV) in AIDS patients requires frequent repetitive injections of intravitreal ganciclovir (GCV). This study was undertaken to establish experimentally whether the intravitreal application of liposomally-entrapped GCV could prolong intraocular therapeutic levels when compared with the intravitreal injection of free GCV, and the clinical effectiveness of this approach in AIDS patients. Intraocular concentration of GCV was determined by means of an ELISA test in rabbit vitreous 2, 3, 7, and 14 days after a single intravitreal injection of either different doses of the free drug (0.2–20 mg) or 1 mg of liposomally-entrapped GCV. After 72 h, only the vitreous of rabbits injected with doses of free GCV greater than or equal to 5 mg showed therapeutic levels of the drug; no GCV was detected after 72 h with any of the doses applied. Moreover, the microscopic study revealed GCV-induced damage in retinal structures in the animals injected with a free GCV dose greater than or equal to 15 mg. Intravitreal injection to rabbits of 1 mg of liposomally-encapsulated GCV showed no retinal toxicity at any of the time points studied, and therapeutic levels were detected up to 14 days after injection (4.67 ± 0.39 g/ml). Five AIDS patients suffering CMV retinitis were injected with 0.5 mg of liposomally-entrapped GCV (2 mg of lecithin). Complete remission of the CMV retinitis was observed already at the third injection of 0.5 mg GCV (one per week) and relapse did not occur during the 2–4 month follow-up of the patients. In view of the results presented, it can be concluded that intravitreal injection of liposomally-encapsulated GCV increases the time period required for reinjections in the treatemnt of CMV retinitis.Abbreviations AIDS acquired immunodeficiency syndrome - AZT zidovudine - CMV cytomegalovirus - GCV ganciclovir     

Regional ocular gentamicin levels after transcorneal and transscleral iontophoresis

Transcorneal and transscleral iontophoresis were compared to subconjunctival injection (control) in the delivery of gentamicin into rabbit eyes. Gentamicin levels in the corena, aqueous, and vitreous were measured by a fluorescence polarization assay at various time intervals after treatment. A mean peak corneal concentration of 376.1 micrograms/ml was achieved 2 hr after transcorneal iontophoresis. This was significantly higher than the level obtained in control eyes (P = 0.016). A mean peak aqueous humor concentration of 54.8 micrograms/ml occurred 2 hr after transcorneal iontophoresis. This was significantly higher than the peak level of 14.2 micrograms/ml after subconjunctival injection (P = 0.003). Inhibitory levels (approximately 5 micrograms/ml) were maintained in both aqueous and cornea for 8 hr after transcorneal iontophoresis. After transscleral iontophoresis, the mean peak vitreous humor concentration was 53.4 micrograms/ml at 16 hr and remained inhibitory through 24 hr; the peak aqueous level was 23.2 micrograms/ml and remained inhibitory for 24 hr. Peak drug concentrations in the vitreous were significantly higher than control (P = 0.026). Therapeutic vitreous humor levels were not achievable after transcorneal iontophoresis or subconjunctival injection. Potential corneal toxicity of transcorneal iontophoresis was demonstrated by measuring corneal thickness and endothelial cell counts prior to and 3 days after transcorneal iontophoresis of gentamicin and balanced saline solution (BSS) (control). No significant differences existed between eyes treated with gentamicin compared to those treated with BSS or when pre- versus postiontophoresis of gentamicin in the same eyes were compared. Transcorneal and transscleral iontophoresis may be an effective noninvasive method of delivering inhibitory levels of gentamicin to the cornea, aqueous humor, and vitreous for the treatment of intraocular infections.     

Retinal toxicity of antibiotics: Evaluation by electroretinogram

Toxicity of an intravitreal injection of gentamicin sulfate, disodium sulbenicillin and cefazolin sodium on the retina was investigated by electroretinogram in albino and pigmented rabbits. Recordings were made before injection and 2 hours and 3, 7, 14, and 21 days after injection.Significant differences were found in the susceptibility of the electroretinogram components to various antibiotics as follows. Gentamicin 0.24mg/0.1ml irreversibly abolished all the components examined. Sulbenicillin 4.0, 8.0, or 12mg/0.1ml transiently suppressed the fawave and the oscillatory potentials incrementally with increasing dose. Cefazolin 0.5, 2.0, or 5.0mg/0.1 ml selectively reduced the oscillatory potentials, leaving the a- and b-waves almost unattenuated. The cefazolin-suppressed oscillatory potentials recovered within 14 days after injection.Judging from the most susceptible electroretinogram components to each antibiotic, we recommend intravitreal doses of these antibiotics for clinical use as follows: gentamicin 0.1 mg/0.1 ml, sulbenicillin 2mg/0.1 ml, and cefazolin 0.25mg/0.1 ml.     

Intravitreal versus retrobulbar injections of triamcinolone for macular edema associated with branch retinal vein occlusion

PURPOSE: To compare the short-term effect of intravitreal versus retrobulbar injection of triamcinolone acetonide for the treatment of macular edema caused by branch retinal vein occlusion. DESIGN: Randomized clinical trial. METHODS: Sixty eyes of 60 patients who had macular edema associated with branch retinal vein occlusion were randomly assigned to receive a single intravitreal injection (4 mg) or repeated retrobulbar injections (40 mg, three times) of triamcinolone. These injections (first injection in the retrobulbar group) were given approximately 1 week after focal laser photocoagulation. Using optical coherence tomography, the central retinal (foveal) thickness and total macular volume were measured before and at 1 and 3 months after injection. Visual acuity, intraocular pressure, and the incidence of reinjection were also examined. Fifty-two patients (86.7%) completed the 3-month follow-up. RESULTS: The mean foveal thickness and total macular volume decreased significantly after either intravitreal or repeated retrobulbar triamcinolone injections. Foveal thickness and macular volume were significantly less after intravitreal injection than after repeated retrobulbar injections, although there had been no significant differences at baseline. The percent reductions in foveal thickness and macular volume were also greater after intravitreal injection than after retrobulbar injections. Improvement in visual acuity was significantly better after intravitreal injection than after the retrobulbar injections. The incidence of intraocular pressure rise (to > or =20 mm Hg) was greater in the intravitreal group than in the retrobulbar group, but this was readily controlled by the use of antiglaucoma medications. After completion of the 3-month follow-up, 24 patients (46.2%) underwent reinjection. The need for reinjections was significantly greater in the retrobulbar group than in the intravitreal group (P = .0001). CONCLUSIONS: A single intravitreal injection of triamcinolone is significantly more effective than are repeated retrobulbar injections in reducing macular edema associated with branch retinal vein occlusion, and leads to greater improvement in visual acuity.     

玻璃体腔注射曲氨奈德与bevacizumab 治疗糖尿病性黄斑水肿疗效比较

目的 对比分析玻璃体腔注射曲氨奈德(TA)与抗血管内皮生长因子单克隆抗体(bevacizumab)治疗糖尿病黄斑水肿(DME)的临床疗效.方法 经眼科常规检查和光学相干断层扫描(OCT)检查确诊,共68例82只眼DME患者纳入观察.患者被分成两组进行玻璃体腔注射TA(4mg/0.1ml)或bevacizumab(1.25mg/0.05ml)治疗.TA组37例45只眼,bevaicizumab组31例37只眼,两组在年龄、糖尿病病程、黄斑水肿病程、最佳矫正视力(BCVA)、中心视网膜厚度(CMT)、眼压等方面均无显著差异.比较治疗后4、8、12周两组间BCVA、CMT、眼压的改变.结果 TA组与bevacizumab组在治疗后4 周、8周、12周时视力差异无统计学意义(t=-0.316,0.896、0.879,P=0.754、0.389、0.384).治疗后4周、12周时,TA组比bevacizumab组黄斑水肿有显著下降(t=-1.892、-3.007,P=0.036、0.004),8周时差异无统计学意义(t=-0.362,P=0.722).眼压在治疗后8周、12周时两组差异有统计学意义(t=2.334、2.600,P=0.026、0.015),TA组眼压明显高于bevacizumab组.结论 玻璃体腔注射TA比bevacizumab更早、更有效地降低糖尿病黄斑水肿,并且维持时间更长,此结果还需大样本、多中心的临床随机对照研究.     

Liposome-encapsulated3H-5FU in rabbits

We compared the pharmacokinetics of liposome-encapsulated tritiated 5-fluorouracil (³H-5FU-Lipo) to³H-5FU in buffered saline (³H-5FU-PBS) after subconjunctival or intravitreal injection into rabbit eyes. Liposomes were prepared using phosphatidylcholine, phosphatidic acid, and alpha-tocopherol. Following a unilateral subconjunctival injection of either³H-5FU-Lipo or³H-5FU-PBS, rabbits were sacrificed at 0.5, 1, 4, and 8 hours. Significantly higher (p<0.05) drug levels were achieved with the encapsulated drug in the vitreous at all four time points and in the aqueous at three of four time points.Following bilateral intravitreal injections of 500 µg of 5FU in 0.1 ml, as either³H-5FU-Lipo or³H-5FU-PBS injected rabbits were sacrificed at 0, 6, 12, 24, and 48 hours. Vitreal drug levels were significantly higher (p<0.05) with encapsulated drug at all time points from 6 hours on. At 48 hours, the vitreal level with the encapsulated drug was 578±0.23 µg/ml compared with 1.06±0.07 µg/ml for³H-5FU-PBS.     

Iontophoresis-gentamicin delivery into the rabbit cornea, using a hydrogel delivery probe

PURPOSE: To evaluate the efficacy of penetration of gentamicin into the cornea of rabbits using iontophoresis with a hydrogel-gentamicin containing probe. METHODS: Eight of 10 groups (groups 3-10) of 6 rabbits (one eye per rabbit), underwent corneal iontophoresis using soft stable hydroxyethyl methacrylate hydrogel discs (80% water content) loaded with gentamicin sulphate which were mounted on an iontophoresis probe. The studied current intensities were 0, 0.1, 0.3 and 0.6 mAmp, and the durations of iontophoresis were 10 and 60 sec. Two control groups received 1.4% topical drops of gentamicin every 5 min for 1 hr (group 1) or sub-conjunctival injection of 10 mg gentamicin (group 2). Following sacrifice, aqueous humour was taken, corneas were excised, and gentamicin concentration was determined in aqueous humour and cornea samples. RESULTS: Post-iontophoresis, the concentration of gentamicin in the corneas ranged from high (88.60 +/- 38.64 microg ml(-1)) to very low (0.10 +/- 0.89 microg ml(-1)). Both the control groups and those rabbits treated with current intensity of 0.1 mAmp or greater obtained therapeutic gentamicin levels in the corneas. Use of iontophoresis for 60 sec or current intensity greater than 0.1 mAmp obtained corneal gentamicin levels not different from sub-conjunctival injection. Application of current intensity of 0.1 mAmp or greater gave corneal gentamicin concentrations comparable to topical application of the drug, except when 0.6 mAmp were used for 60 sec (p = 0.05). Increasing current intensity or duration of iontophoresis significantly increased (p = 0.001 for both) gentamicin penetration into the cornea. Current intensity had more influence (Beta2 = 0.40) than duration (Beta2 = 0.13) on drug penetration. A significant interaction was found between the duration of iontophoresis and the current intensity. Very small or no concentrations of the drug were discovered in the anterior chambers of rabbits. CONCLUSIONS: Iontophoresis using hydrogel-gentamicin probe may deliver therapeutic concentrations of gentamicin into the cornea.     

Intravitreal delivery of oligonucleotides by sterically stabilized liposomes.

PURPOSE: The efficacy of sterically stabilized liposomes for delivering a model phosphodiester oligonucleotide intravitreally was investigated in the rabbit. METHODS: Ocular distribution and clearance from the vitreous humor of a model 16-mer oligothymidylate (pdT16) were evaluated in the rabbit by radioactivity measurements after intravitreal injection of either a solution or liposomes containing the [33P]pdT16 oligonucleotide. The integrity of pdT16 was investigated using a competitive hybridization assay. RESULTS: The residual concentration of the [33P]pdT16 oligonucleotide within the ocular tissues was significantly increased after intravitreal administration of the liposomal suspension compared with a simple solution. Administration of liposome-encapsulated pdT16 oligonucleotide resulted in sustained release into the vitreous and the retina-choroid compared with release from the solution and in a reduced distribution to nontarget tissues (sclera, lens). In addition, liposomes protected the phosphodiester oligonucleotide against degradation. This was not observed after administration of the free oligonucleotide. CONCLUSIONS: The intravitreal injection of a phosphodiester oligonucleotide encapsulated within liposomes is a new way of delivering intact oligonucleotide to the eye in a controlled manner. This offers interesting prospects for the treatment of retinal diseases.     

Pharmacokinetics of intravitreal injection. Assessment of a gentamicin model by ocular dialysis

Intravitreal drug administration is the treatment of choice for bacterial endophtalmitis, but improved knowledge of vitreal pharmacokinetics is essential for the development of optimal antibiotic regimes. We used our recently developed sampling device to estimate vitreal gentamicin concentrations for up to 30 hr after an intravitreal bolus injection of gentamicin. The device is based on the principle of dialysis, whereby a constant flow rate of dialysate through a loop of dialysis fiber in the vitreous attains a gentamicin concentration proportional to the intravitreal gentamicin level around the fiber. The dialysate is continuously recovered and the collected samples then assayed for gentamicin. Normal cat eyes and those with induced bacterial endophthalmitis formed the two groups tested. Concentration-time data fitted well to an open single compartment pharmacokinetic model that incorporated the processes of transfer of drug from the injection site to the sampling site (a function of diffusion within the vitreous), and the elimination from the sampling site (a function of elimination from the vitreous). The initial phase of transfer between the injection and sampling site was rapid and rates were comparable in the two groups. Elimination rate constants were uniformly greater in infected eyes than in controls (0.107 hr-1 compared to 0.055 hr-1). Aqueous humor gentamicin concentrations in control eyes varied between 3 and 6 times those found in fellow infected eyes at the end of each experiment. Accelerated elimination of gentamicin from the vitreous body of eyes with endophthalmitis may be explained by increased permeability of the blood-retinal barrier.     

Duration of therapeutic levels of intravitreally injected liposome-encapsulated clindamycin in the rabbit

We investigated an intravitreal preparation of liposome-encapsulated clindamycin phosphate to determine the duration of therapeutic levels of the drug in the vitreous cavity. Twenty New Zealand albino rabbits were given an intravitreal injection of 750 micrograms/0.1 mL of encapsulated clindamycin (10 animals) or 800 micrograms/0.1 mL of nonencapsulated clindamycin (10 animals) and then were killed immediately or 6, 12, 24 or 48 hours later. The mean concentration of encapsulated clindamycin in the vitreous at 48 hours was 28.4 micrograms/mL, while that of nonencapsulated clindamycin at 24 hours was 2.3 micrograms/mL. The estimated elimination rate of nonencapsulated clindamycin was 3 hours, compared with approximately 10 hours for the encapsulated preparation. This drug delivery system warrants further investigation for possible use in humans.     

Intraocular antibody synthesis during experimental uveitis

Determination of intraocular antibody synthesis against certain microorganisms is a diagnostic aid in identifying the causative agent in clinical uveitis. Little is known, however, concerning the kinetics and specificity of antibodies produced during intraocular inflammation. To investigate this subject we induced uveitis in rabbits by injecting small amounts of human serum albumin (HSA) into the vitreous. Aqueous humor and serum were taken before and after the induction of uveitis and levels of total IgG, rabbit albumin and anti-HSA-IgG were determined. The anti-HSA-IgG was quantitated using immunoaffinity purified anti-HSA-IgG as a standard. Six weeks after intravitreal HSA injection, high levels of total IgG (4.7 mg/ml) and albumin (15.4 mg/ml) were observed in the aqueous as compared to control eyes (IgG: 0.12 mg/ml; albumin: 0.48 mg/ml). Using albumin to correct for blood aqueous barrier breakdown we calculated that only 0.6% of the locally synthesized IgG was directed against intravitreally injected HSA. Two months after the intravitreal injection of HSA the main signs of the uveitis had subsided. A recurrent uveitis was subsequently induced by an intravenous HSA injection. This resulted in a marked increase of total IgG (14.3 mg/ml) and albumin (24.6 mg/ml) in the aqueous humor of the uveitis eyes. It was remarkable that the mean anti-HSA-IgG level (0.62 mg/ml) in the uveitis eyes was higher than that seen in serum (0.41 mg/ml). After this secondary uveitis, 9% of the locally synthesized antibodies were directed against HSA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modified high-performance liquid chromatography technique for detection of vancomycin in human vitreous

PURPOSE: To standardize the technique and methodology for estimating the level of vancomycin in human vitreous using a modified high-performance liquid chromatographic method. METHODS: Sample preparation involved spiking the vitreous with known quantities of the drug followed by a brief treatment with 30% trichloroacetic acid. Samples were analyzed on a C18 reverse-phase column using a mobile phase of 50 mM phosphate buffer (pH 4.0) and 10% acetonitrile. RESULTS: Vancomycin was detected at 198 nm. It showed a retention time of 2.2 min in the vitreous. A linear increase in the area under the peak corresponding to the drug was observed with increase in concentration of vancomycin in the vitreous. The method was applied to detect the vancomycin levels in vitreous of 5 patients with exogenous endophthalmitis, 24-48 h after intravitreal injection of vancomycin 1 mg/0.1 ml. The mean concentration of vancomycin in these samples was 120.022 +/- 59.87 microg/ml (43.859-179.09 microg/ml). The present technique allowed a quantification limit of 1 microg/ml. CONCLUSION: This technique is suitable to estimate vancomycin levels in human vitreous in a variety of clinical and experimental studies. It has the added advantages of being less expensive, simple and rapid.     

兔眼玻璃体腔注射抗血管内皮生长因子单克隆抗体Bevacizumab的视网膜毒性研究

目的 观察不同剂量抗血管内皮生长因子单克隆抗体Bevacizumab兔眼玻璃体腔注射的视网膜毒性作用。 方法 16只新西兰无色素兔的32只眼随机分为药物注射组和对照组，药物注射组又根据玻璃体腔注射药物剂量不同分为A、B、C组，玻璃体腔注射Bevacizumab剂量分别为0.05、0.10、0.25 ml，分别含Bevacizumab 1.25、2.50、6.25 mg。对照组玻璃体腔注射0.9％生理盐水0.10 ml。注药后1、2、4周行视网膜电图（ERG）检查。另外 ，在兔眼玻璃体腔注射Bevacizumab后1、2、4周，每组各摘除2只兔眼，行视网膜组织形态及超 微结构的光学显微镜和透射电子显微镜观察。 结果 兔眼玻璃体腔注射 Bevacizumab后1、2、4周，兔眼ERG各项反应波形均正常，振幅均未出现异常改变（P＞0.05）。光学显微镜下观察 ，药物注射组和对照组视网膜各层组织形态在各时间点均未见异常。透射电子显微镜观察， A、B组与对照组无明显差异；C组视网膜光感受器细胞出现部分线粒体损伤，发生肿胀和积 水变，4周时病变无缓解。 结论 单次兔眼玻璃体腔注射Bevacizumab 1.25 mg或2.50 mg是安全的。 （中华眼底病杂志，2008，24：193-196）     

Effect of intravitreal dexamethasone on vitreous vancomycin concentrations in patients with suspected postoperative bacterial endophthalmitis

Purpose To study intravitreal dexamethasone and vancomycin concentrations, when used together in patients with suspected postoperative bacterial endophthalmitis. Animal studies had suggested that dexamethasone might decrease the concentration of vancomycin. Design Prospective randomized clinical trial in a tertiary referral center. Methods Twenty-nine consecutive patients with suspected postoperative bacterial endophthalmitis underwent a vitreous biopsy followed by intravitreal injection of antibiotics (0.2 mg vancomycin, 0.05 mg gentamicin) and 400 μg dexamethasone or placebo. After 3–4 days, the intravitreal injection of antibiotics and dexamethasone or placebo was repeated. In 18 patients, a second biopsy was taken for repeat culture and measurement of vancomycin and dexamethasone concentrations. Results In 20/29 patients (69%) the first vitreous cultures were positive; the second culture was negative in all cases. Thirteen out of 29 patients received dexamethasone. Dexamethasone concentrations showed an average of 25 ng/ml 3 days after injection, with an estimated half-life of 5.5 h. Vancomycin concentrations in patients given dexamethasone tended to be higher compared with those in the placebo group (P=0.061). Conclusion Intravitreal dexamethasone does not lead to decreased vancomycin concentrations, when given simultaneously in the treatment of patients with suspected bacterial endophthalmitis.     

玻璃体内注药药物含量的模拟测定

目的：探讨玻璃体内注药时药液稀释后药物含量的准确性及推荐使用一种相对准确的药液稀释方法。方法：以盐酸普鲁卡因为抗生素替代物，用不同方法稀释药液，分光光度计测定吸收度并计算药物含量进行比较。结果：在一次性1ml注射器内稀释药液不易混匀，与使用微量移液器精确量取的方法比较，药物含量的差异有显著性；在5ml注射器内稀释并混匀药液，再以1ml注射器抽取混合均匀的溶液，与使用微量移液器精确量取的方法比较，差异无显著性。结论：在体积相对大的容器内稀释药液并充分混匀；使用一次性1ml注射器吸取药液能达到要求的准确度，操作时应精确抽取药物，保证剂量准确。     

Benzalkonium chloride and gentamicin cause a leak in corneal epithelial cell membrane

The purposes of this study are to characterize the pathophysiological effects of benzalkonium chloride and gentamicin on corneal epithelial cells and to determine the concentration dependent effect of these agents on membrane currents of these cells. Rabbit corneal epithelial cells were isolated and subdivided into small, medium and large cells according to their cell capacitance. Using whole cell clamp technique, potassium current of corneal epithelial cells was recorded. Transmembrane current was measured again after bathing in benzalkonium chloride 1, 3, 10, 30 and 100 micrometer ml(-1)for 3 min. The effect of gentamicin was tested at concentrations of 0.4, 1.0, 2.0, 4.0 and 10 mg ml(-1). Synergistic effect of gentamicin of the above mentioned concentrations in the presence of benzalkonium chloride 1 microgram ml(-1)was also measured. We found that small corneal epithelial cells had the highest depolarization-gated, outward potassium current density and large cells had the lowest current density, while medium cells had a current density in between. Benzalkonium chloride induced a concentration dependent increase in the leak current with increasing concentration from 1 to 100 microgram ml(-1). The increase of leak current in medium and large cells was less than that in the small cells. Gentamicin also caused a concentration dependent increase in leak current density from 0.4 to 10.0 mg ml(-1). The increase in leak current density was statistically significant when the concentration was 2.0 mg ml(-1)or higher in small corneal epithelial cells and 1.0 mg ml(-1)or higher in the medium and large cells. Benzalkonium chloride 1.0 microgram ml(-1)augmented the effect of gentamicin on epithelial cell membrane. The extent of enhancement was more prominent in larger than smaller cells. Using whole-cell clamp technique, we were able to determine the threshold concentration of gentamicin and benzalkonium chloride on the integrity of corneal epithelial cell membrane. The toxic action of both agents is mediated by an increase in leak current. We propose that the whole-cell clamp technique is a sensitive and useful tool in determining cytotoxic effects of various agents.