Hydrophilic IOL shows potential for antibiotic delivery

A study conducted in rabbit eyes showed that implantation of a hydrophilic IOL (Afinity Single Piece Collamer IOL, STAAR Surgical) presoaked in antibiotic may provide a method for delivering sustained, therapeutic intraocular concentrations of antibiotic following cataract surgery.

Key Points

Chicago-Results from a preclinical study demonstrate that at least one type of hydrophilic IOL (Afinity Single Piece Collamer IOL, STAAR Surgical) may provide a viable system for delivering high concentrations of antibiotic into the anterior chamber after cataract surgery, reported Lisa M. Nijm, MD, JD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

The study was performed in rabbit eyes and evaluated aqueous humor concentrations achieved when the hydrophilic IOL was soaked in moxifloxacin or cefuroxime for varying periods of time. The results showed that the peak intraocular levels of antibiotic achieved far exceeded the MIC90 values for most important endophthalmitis pathogens.

"This research suggests this hydrophilic IOL may be used as a drug delivery system for the prevention of endophthalmitis. Further studies are needed to determine the optimal soak time for maximizing efficacy while minimizing potential toxicity. Additional research is also needed to investigate use of IOLs for the delivery of medications other than antibiotics and the performance of other hydrophilic IOLs," said Dr. Nijm, senior resident, Department of Ophthalmology, University of Illinois, Chicago.

Choice of lens, antibiotic

"The choice of IOL and antibiotic were important considerations. A hydrophilic IOL was used because, when soaked in an antibiotic solution, hydrophobic IOLs do not absorb the medication. We decided to study moxifloxacin and cefuroxime due to recent clinical interest in their use for intracameral injection after cataract surgery," Dr. Nijm said.

The in vivo study was performed in white New Zealand rabbits that underwent bilateral standard phacoemulsification followed by implantation of an IOL presoaked in moxifloxacin 0.5% into one eye and an IOL soaked in cefuroxime 0.1% in the fellow eye. The IOL soaking periods varied for each antibiotic.

Concentrations of antibiotic in the aqueous humor were determined by assay of 0.1-ml aliquots withdrawn after 30 minutes and 2, 4, 6, and 24 hours. In an aggregate analysis of data from all animals, the peak aqueous humor concentration of moxifloxacin was 74 μg/ml and occurred at about 2 hours post-IOL implantation. Results from later time points, however, showed levels of moxifloxacin remained above the MIC90 for Staphylococcus epidermidis for at least 24 hours.

The peak concentration of cefuroxime was 7.5 μg/ml and was recorded at 30 minutes. Thereafter, the mean aqueous humor concentrations decayed more rapidly than did the moxifloxacin concentrations. At 24 hours, the mean concentration of cefuroxime in the aqueous humor was 0.69 μg/ml, which was below the MIC90 value for S epidermidis.

"These results need to be interpreted with the understanding that the starting concentration of cefuroxime was lower than that of moxifloxacin, 0.1% versus 0.5%, and the soaking times were also less for the cefuroxime group," Dr. Nijm said.

"The primary purpose of this study was to evaluate whether the chosen IOL was able to uptake and release antibiotic in a time-dependent fashion at high enough concentrations to prevent potential development of endophthalmitis," she said. "We were able to demonstrate this successfully with both moxifloxacin and cefuroxime. However, we also varied the soaking time between the two antibiotics in the interest of seeing if it might be possible to achieve acceptable levels with a shorter soaking period. Further studies will need to be done to determine optimal soaking time."

Dr. Nijm added that using an IOL as an antibiotic delivery system offers many potential benefits. In contrast to topical treatment, it allows direct delivery of medication into the anterior chamber. It also avoids the issue of patient adherence to therapy, which can occur with topical medication use. Compared with intracameral antibiotics, IOL-based delivery provides safer peak levels and has the potential to provide sufficient antimicrobial coverage for a longer duration.

"However, with any intraocular administration of antibiotic, we must also consider the potential for the antibiotic to affect the IOL and for medication-related intraocular toxicity. Additional study is required, although our initial pathology studies show no evidence of endothelial or retinal toxicity in this model," she said.

Dr. Nijm's previous work in this area has been presented at the 2007 Ocular Microbiology and Immunology Group (OMIG) meeting (Nijm LM, Tu EY, Ulanski II LJ, Fiscella Jr. R, Peterson R. Utilizing a hydrophilic intraocular lens for intraocular drug delivery. Presented at: Annual meeting of Ocular Microbiology and Immunology Group. 2007; New Orleans).

Dr. Nijm said that the overall results of this research are very promising. She plans to continue this work in the coming year during her corneal fellowship at University of California Davis, Sacramento.