pH of anti-VEGF agents in the human vitreous: low impact of very different formulations

BACKGROUND The aim of the study was to measure pH changes of the human vitreous caused by the intravitreal drugs bevacizumab, ranibizumab, aflibercept, and ziv-aflibercept. METHODS Fresh human vitreous samples were obtained during core vitrectomy (23-gauge) from patients with epiretinal gliosis. Aliquots of bevacizumab, ranibizumab, aflibercept or ziv-aflibercept (2 µl) were added consecutively to 200 µl of vitreous samples or 0.9% NaCl saline. The pH was measured using a pH-sensitive microelectrode. Rituximab, in off-label use against intraocular lymphoma, was tested as an IgG1 antibody. RESULTS The pH of the administered drugs was 5.91 for bevacizumab (95% CI 5.63-6.19), 5.32 for ranibizumab (95% CI 5.0-5.63), 6.05 for aflibercept (95% CI 5.78-6.31), ziv-aflibercept 6.1 (95% CI 6.05-6.15), and 6.29 for rituximab (95% CI 5.97-6.61). While the fresh and undiluted vitreous fluid showed pH values of 7.0-7.4, pH values increased if saline or rituximab were added. In contrast, the pH decreased slightly if aflibercept, bevacizumab, ranibizumab or ziv-aflibercept were supplemented. The observed pH decreases were not significant after ranibizumab was added. Significant changes were only notable with higher-than-normal amounts of bevacizumab (26-40 µl). The vitreous showed the most robust buffering capacity towards ranibizumab and rituximab. CONCLUSIONS The pH changes in vitreous samples elicited by the usual intravitreal anti-VEGF drugs differed clearly, but only by much higher concentrations than used in the clinical routine. Although the ingredient solution of ranibizumab showed the lowest pH, it caused only moderate changes of vitreal pH compared to bevacizumab, aflibercept or ziv-aflibercept.