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Angela Jiang, Jillian Wang, Cedric Pratt, Michelle Carlton, George Hinkle, Michael V. Knopp, John Christoforidis; Serum Levels Of Intravitreally Placed I-124 Bevacizumab And I-124 Ranibizumab In A Rabbit Model Following Lensectomy, Vitrectomy And No Surgery. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2964.
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To determine the serum levels of I-124 bevacizumab and I-124 ranibizumab after intravitreal injection following lensectomy and vitrectomy and to compare these with non-operated eyes in a rabbit model.
Six Dutch-belted rabbits underwent pars plana vitrectomy (PPV), 6 rabbits underwent pars plana lensectomy (PPL) and 6 rabbits served as non-surgical controls. Twelve days following the surgical procedures, each operated eye underwent an intravitreal injection consisting of 0.5 mg/0.05 ml I-124 labeled ranibizumab or 1.25 mg/0.05 ml I-124 labeled bevacizumab. Serum levels from each rabbit were drawn on days 2, 5, 7, 14, 21, 28 and 35. Serum radioactivity levels in counts/min for I-124 bevacizumab and I-124 ranibizumab were measured with a gamma counter (Perkin Elmer-Wizard 2).
Serum radioactivity measurements with standard deviations on day 2 for I-124 bevacizumab were 51,314 (+/-9,425) counts/min for non-surgical controls, 175,248 (+/-19,724) counts/min after PPV and 230,330 (+/-6523) counts/min after PPL. For I-124 ranibizumab these values were 6,531 (+/- 5,619) counts/min for non-surgical controls, 2,474 (+/-486) counts/min after PPV and 4,722 (+/-2,957) counts/min after PPL. The serum half-lives with standard deviations of elimination for I-124 bevacizumab were 16.84 (+/-7.23) days for non-surgical controls, 2.49 (+/- 0.07) days after PPV and 3.91 (+/-1.39) days after PPL. For I-124 ranibizumab the half-lives were 3.81 (+/-1.65) days for non-surgical controls, 3.56 (+/-0.30) days after PPV and 2.78 (+/-0.52) days after PPL.
Serum levels were higher for I-124 bevacizumab than I-124 ranibizumab at all time points for all three study groups. The serum levels of I-124 bevacizumab were elevated following lensectomy and vitrectomy compared to non-surgical eyes following intravitreal injection, while no such pattern was present for I-124 ranibizumab. The half-life of I-124 bevacizumab was prolonged in non-surgical eyes presumably due to a slower release from the vitreous cavity, while the half-lives for I-124 ranibizumab did not differ between treatment groups. Measurement of serum radioactivity levels of intravitreally placed radiolabeled intravitreal agents represents a novel technique for quantitating agent serum levels.
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