Abstract
Purpose: :
To determine the anatomic characteristics and pharmacokinetic properties of intravitreally-placed I-124-bevacizumab and I-124-ranibizumab after pars plana lensectomy or pars plana vitrectomy and to compare these with non-operated eyes in a rabbit model.
Methods: :
Six Dutch-belted rabbits underwent pars plana vitrectomy, 6 rabbits underwent pars plana lensectomy and 6 rabbits served as non-surgical controls. Radiolabeling with I-124 was completed using a modified Iodogen method. Twelve days after surgery and after confirming radiochemical purity, three anesthetized rabbits from each group underwent intravitreal injection with I-124-bevacizumab and three with I-124 ranibizumab. All rabbits and phantoms of I-124- bevacizumab and I-124-ranibizumab were imaged with a Micro PET-CT scanner on days 0, 2, 5, 7, 14, 21 and 28.
Results: :
The intravitreally placed radiolabeled agents were found to be contained within the vitreous cavity for the duration of the study with no extravasation into the central nervous system or elsewhere. I-124 bevacizumab was detectable until day 26 in unoperated eyes, 22 days after vitrectomy and 19 days after lensectomy. I-124 ranibizumab was detectable until day 21 in unoperated eyes, 19 days after vitrectomy and 13 days after lensectomy. The kinetic model appears to represent a 2-compartment model in all subgroups and the average half-lives with standard deviations for bevacizumab and ranibizumab after correction for radioactive decay were found to be 4.22 (+/- 0.12) days and 2.81 (+/- 0.08) days respectively in unoperated eyes, 2.30 (+/- 0.10) and 2.13 (+/- 0.12) after vitrectomy and 2.08 (+/- 0.13) and 1.79 (+/- 0.02) days after lensectomy.
Conclusions: :
Intravitreal half-lives were longer for bevacizumab than ranibizumab within all three groups and was greatly reduced following vitrectomy and lensectomy for both agents. The retention properties in unoperated eyes were consistent with those of previously published immunoassay methods. Consideration may be made for more frequent intravitreal anti-VEGF dosing regimens may be made in eyes following vitrectomy and lensectomy.
Keywords: imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • vitreous