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Nishanthan Srikantha, Klaus Suhling, Tim Jackson; Translational diffusion of ranibizumab and bevacizumab as measured by Fluorescence Recovery after Photobleaching (FRAP). Invest. Ophthalmol. Vis. Sci. 2012;53(14):6488.
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Some clinical studies indicate that the 149,000 Dalton bevacizumab and 48,000 Dalton ranibizumab have similar therapeutic effects. It would be expected that ranibizumab is more effective as its lower molecular weight should facilitate diffusion through the vitreous body to the retina. This study aimed to determine the diffusion coefficient of both drugs.
The translational diffusion of fluorescently labeled ranibizumab and bevacizumab were determined using fluorescence recovery after photobleaching (FRAP). The translational diffusion coefficient was used to calculate an approximate size for both drugs, and to predict the speed of diffusion through vitreous.
Studies show that porcine vitreous is 6.29 ± 2.3centipoise (cp). At this viscosity the diffusion coefficient for ranibizumab and bevacizumab is 2.08x10-13and 1.50x10-13 repectively. Based on translational diffusion coefficients, ranibizumab has a molecular radius of 6.43nm and bevacizumab 9.00nm. These results predict that ranibizumab would diffuse through vitreous 1.39 times faster than bevacizumab.
Ranibizumab is able to reach its target tissue faster than bevacizumab. The effects on drug elimination is harder to predict, but the results are consistent with animal studies showing that ranibizumab has a shorter half-life than bevacizumab. Further studies are needed.
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