PET/CT Imaging of I-124-Radiolabeled Bevacizumab and Ranibizumab after Intravitreal Injection in a Rabbit Model

PURPOSE. To determine whether bevacizumab and ranibizumab remain confined within the vitreous cavity after intravitreal injection and to determine the pharmacokinetic properties of these agents within the vitreous cavity. METHODS. Radiolabeling with I-124 was completed using a modified Iodogen method. After testing for radiochemical purity, three anesthetized Dutch-belted rabbits underwent intravitreal injection with I-124 bevacizumab, and three underwent it with I-124 ranibizumab. All rabbits were imaged with a Micro PET-CT scanner on days 0, 2, 5, 7, 14, 21, 28, and 35. 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 28, whereas I-124 ranibizumab was detectable until day 21. The kinetic model appears to represent a two-compartment model, and the average retention times for bevacizumab and ranibizumab after correction for radioactive decay were found to be 4.2 days and 2.8 days, respectively. CONCLUSIONS. There was no significant escape of bevacizumab and ranibizumab from the vitreous cavity after intravitreal injection. After correction for radioactive decay, both agents remained detectable until 28 and 21 days, respectively, with retention properties that validated those methods reported in previous studies. (Invest Ophthalmol Vis Sci. 2011;52:5899-5903) DOI: 10.1167/iovs.10-6862