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One-year results of switching to aflibercept for persistent diabetic macular edema resistant to bevacizumab

PURPOSE: The aim of this study is to evaluate the functional and anatomical effects of switching from bevacizumab to aflibercept in patients with persistent diabetic macular edema (DME) resistant to bevacizumab. MATERIALS AND METHODS: Patients with DME refractory to bevacizumab (1.25 mg/0.05 mL) were subsequently switched to aflibercept. The included patients received five loading doses of intravitreal aflibercept (2 mg/0.05 mL) given monthly. After the loading dose, aflibercept was injected every 2 months. The follow-up duration was 1 year. RESULTS: The study consisted of 37 eyes of 37 patients. The mean age of the participants was 56.81 ± 7.11 years. The mean central macular thickness at baseline was 428.32 ± 84.89 μm, which decreased significantly to 275.54 ± 50.24 μm (P < 0.003). There was a significant improvement in the mean best-corrected logMAR visual acuity from 0.627 ± 0.307 at baseline to 0.203 ± 0.235 (P < 0.017) at the end of follow-up. CONCLUSIONS: Aflibercept is effective in patients with persistent DME not responsive to bevacizumab.


Introduction
D iabetic macular edema (DME) is the most important cause of diminution of vision in diabetic patients. [1] Risk factors of DME include long duration of diabetes mellitus (DM) and poor metabolic control. DME occurs in about 20% of diabetic patients. [2] Macular laser treatment was considered the treatment of choice for DME according to the results published in the Early Treatment Diabetic Retinopathy Study back in the 80s. [3] Hyperglycemia in diabetics is responsible f o r t h e d e s t r u c t i o n o f t h e b l o o d -retinal barrier and damage to capillary endothelial cells. [4] One of the main involved mediators is vascular endothelial growth factor (VEGF), which leads to new vessels' formation and hyperpermeability of the blood vessels. [5] The use of drugs antagonizing VEGF effects was a breakthrough in DME management. [6] This category of anti-VEGF agents includes three main drugs: the full-length VEGF-A monoclonal antibody bevacizumab (Avastin; Genentech, Inc., San Francisco, CA, USA). Although it is not approved by the United States Food and Drug Administration (FDA) for intraocular use, bevacizumab is widely used according to the results of many studies, for example, the Bevacizumab or Laser Treatment in the Management of Diabetic Macular Edema (BOLT) study. [7] Ranibizumab (Lucentis; Genentech, Inc., San Francisco, CA, USA) is a VEGF-A monoclonal antibody fragment. Ranibizumab was shown to be effective in the RISE and RIDE studies. It gained FDA approval as an intravitreal anti-VEGF drug for DME management. [8] The most recent drug, aflibercept (Eylea; Bayer Pharma AG, Berlin, Germany), is a fusion protein that acts as a decoy receptor binding all VEGF-A isoforms, VEGF-B, and placental growth factor (PlGF). It gained FDA approval in DME management after the results of the VIVID and VISTA studies. [9] Recently, a direct comparison between the three drugs in the treatment of DME was published by the Diabetic Retinopathy Clinical Research Network (Protocol T). The results showed that when baseline diminution of vision was not severe (>20/40), the three drugs produced the same results. However, when the initial best-corrected visual acuity (BCVA) was more affected (<20/50), a more functional benefit was noticed in the aflibercept group. [6] Due to its lower price, bevacizumab intravitreal injection is the first-line treatment of DME in many parts of the world. [10] It produces good results in many patients suffering from DME. However, even in patients with improved vision, it is not uncommon to see persistent fluid on optical coherence tomography (OCT) in bevacizumab-treated patients undergoing monthly injections. [11] Despite regular monthly treatment, a group of patients shows an incomplete response to anti-VEGF agents. According to Protocol T, after 6 monthly injections, 41% of bevacizumab group had persistent central macular edema in contrast with 27% of patients in the aflibercept group. [6] The presence of chronic fluid in the macula can cause permanent structural damage in the retina leading to irreversible visual loss. [12] Many studies reported that a group of DME patients has a poor response to bevacizumab. [11,13] Since aflibercept has some theoretical advantages over bevacizumab, it seems logical to convert their treatments to aflibercept in order to obtain better results. [14] Several studies reported different outcomes following this approach. [15][16][17] The aim of this study is to prospectively document the functional and anatomical effects of switching from bevacizumab to aflibercept in patients with persistent DME resistant to bevacizumab.

Materials and Methods
This prospective interventional case series was conducted in accordance with the tenets of the Declaration of Helsinki. The study was approved by the university ethics committee (Alexandria faculty of medicine etics committee: IRB No:00007555-FWANO:00018699). Informed consent was obtained from all study patients before participating in the study.
Patients with DME refractory to bevacizumab (1.25 mg/0.05 mL) were subsequently converted to aflibercept (2 mg/0.05 mL). Eligible patients were diabetic patients, older than 18 years, center-involving DME, and central macular thickness (CMT) > 300 μm by spectral-domain OCT (SD-OCT) performed with the commercially available Cirrus HD-OCT Model 4000 (Carl Zeiss Meditec, Dublin, CA, USA). The mean CMT was measured in the 1 mm central and was automatically generated. Included eyes must have received six consecutive monthly intravitreal injections of bevacizumab for the treatment of DME, presenting with persistent central fluid and CMT > 300 μm 1 month after the last bevacizumab injection. The BCVA must be better than 0.05 decimal visual acuity (1.3 logMAR). Only one eye from each patient was included in the study. If both eyes met the inclusion criteria, the eye with worse visual acuity was included. The other eye was treated but not included in the study.
Patients were excluded if they had dense media opacity, pregnancy, previous intravitreal steroid therapy, uncontrolled DM (HbA1c ≥10%), and prior intraocular surgery (with the exception of uneventful cataract surgery > 6 months prior to conversion). Other exclusion criteria included active proliferative diabetic retinopathy, tractional maculopathy, macular ischemia, and other ocular diseases: age-related macular degeneration (AMD), central/branch retinal vein occlusion, and glaucoma.
Decimal BCVA was used and converted into logarithm of the minimal angle of resolution (logMAR). The baseline data were recorded 1 month after the last Bevacizumab injection. The first intravitreal aflibercept injection was given after a washout period of 1 month.
Included patients were given 5 monthly injections of intravitreal aflibercept (2 mg/0.05 mL) (Eylea; Bayer, Berlin, Germany). Then, additional injections were given every 2 months. The follow-up duration was 1 year. Included patients were subjected to baseline evaluation, then monthly after the first aflibercept. At each visit, a complete ophthalmic examination was done, including BCVA assessment on a decimal chart and CMT measured using SD-OCT (Carl Zeiss Meditec, Dublin, CA, USA).
Fluorescein angiography was performed using a Kowa VX-10α Fundus camera (Kowa Company Ltd., Nagoya, Japan) at the initial visit and at the end of follow-up.
Intravitreal aflibercept injections were performed in the operating room using a strict aseptic technique. Topical anesthetic drops were given. Sterilization by povidone-iodine was done. 30-gauge needles were used to give the intravitreal injections.
Statistical analysis was done using the Statistical Package for Social Sciences (SPSS, version 22; SPSS Inc., Chicago, Illinois, USA). The statistical tests used were as follows: number and percentage of each category, mean and standard deviation for each parameter, Mann-Whitney U-test for comparison of non-parametric data, T-test for comparison of parametric data, and Pearson correlation coefficient for finding the correlation between two variables. The 5% was chosen as the cutoff level of significance.
The mean CMT before initiating bevacizumab injections was 460.15 ± 85.20 μm which only was mildly improved to 428.32 ± 84.89 μm after the 6 monthly bevacizumab injections before switching to aflibercept.
The mean best-corrected logMAR visual acuity before initiating bevacizumab injections was 0.720 ± 0.260 which only was mildly improved to 0.627 ± 0.307 after the 6 monthly bevacizumab injections before switching to aflibercept.
The pattern of baseline DME before switching was as follows: combined diffuse and cystoid DME was present in all 37 patients (100%), while subretinal fluid was present in 9 patients (24.3%). Vitreomacular adhesion at the macula was detected in 3 patients (8.1%), while epiretinal membrane at the baseline was detected in 2 patients (5.4%).
All patients had previous 6 monthly intravitreal bevacizumab injections over a 6-month period. All patients completed 12-month follow-up after the first aflibercept injection. All patients received 8 aflibercept injections: 5 monthly loading dose and 3 bimonthly injections. The final data were recorded 2 months after the 8 th injection at the 12-month follow-up visit.

Anatomical outcomes after switching to aflibercept
The mean CMT at baseline was 428.32 ± 84.89 μm, which decreased significantly to 275.54 ± 50.24 μm (P < 0.003). The change in CMT over the study duration is illustrated in Figure 1. There was a decrease in CMT at different follow-up visits, and this was statistically significant, starting from the 2 nd month till the end of the study. All patients had reduced CMT at the end of the follow-up compared to their baseline values. Twenty-eight patients (75.7%) had more than 50 μm reduction in CMT at the end of follow-up compared to baseline, while 9 patients (24.3%) had < 50 μm reduction in CMT [ Table 1].

Functional outcomes after switching to aflibercept
There was a significant improvement in the mean best-corrected logMAR visual acuity from 0.627 ± 0.307 at baseline to 0.203 ± 0.235 (P < 0.017) at the end of follow-up. Figure 2 shows the change in the BCVA at different time points of the study. After switching from bevacizumab to aflibercept, BCVA improved in 34 eyes (91.9%), remained stable in 3 eyes (9.1%), and there were no cases of deterioration of visual acuity. There was an improvement in visual acuity from the 1 st month of follow-up, but it reached a statistically significant level from the 5 th follow-up visit till the end of follow-up. At baseline, 11 patients (29.7%) had 6/60 (0.1 decimal VA) or less visual acuity, while at the end of followup, all patients had visual acuity better than 6/60. The initial visual acuity of 6/12 or better was present in 3 patients (8.1%), in comparison with 24 patients (64.9%) at the end of the study [ Table 2]. Figures 3 and 4 show the OCT of a case at baseline and at the end of follow-up.
There were no significant correlations between baseline characteristics and the anatomic or functional improvement, except for one baseline factor: initial CMT. Baseline CMT more than 400 μm was associated with a significant decrease in CMT and significant visual acuity improvement compared to baseline CMT < 400 μm.
There were no recorded cases of major complications of intravitreal injections either ocular or systemic. Only mild subconjunctival hemorrhage was recorded after 15 injections out of 296 (5% of injections).

Discussion
Intravitreal anti-VEGF injections became the treatment of choice for center-involving DME. Bevacizumab, although not FDA approved, is widely used because of its low cost. [6] Not all patients respond well to bevacizumab, so the idea of switching to aflibercept was considered. [15][16][17] Aflibercept molecule is different from other anti-VEGF agents: It binds VEGF-A with over 100 times stronger than either ranibizumab or bevacizumab. [18] Aflibercept additionally binds VEGF-B and PlGF, which both have been implicated in the pathogenesis of DME. [19] Aflibercept, unlike bevacizumab, does not contain murine antibody components, which can initiate a systemic immune response leading to tachyphylaxis. Conversion to aflibercept may overcome any previous tolerance to anti-VEGF proteins. [20]    Multiple studies were reported regarding the effects of switching between anti-VEGFs in exudative AMD. Switching to aflibercept in wet AMD showed variable results. In general, there was an anatomical improvement with less visual benefit. [21][22][23] Recently, few studies reported short-term results about the switch from bevacizumab to aflibercept in resistant cases of DME. [15][16][17] This study aimed to prospectively document the 1-year outcome of switching to aflibercept in bevacizumab resistant cases of DME. Our results show a statistically significant benefit, both anatomically and functionally after switch to aflibercept.
One previous retrospective study [17] included 50 eyes converted to aflibercept after prior ranibizumab or bevacizumab injections. Patients had a high number of injections (mean: 13.7) before the switch. The mean number of aflibercept injections was 4.1 and the follow-up duration after the switch was 4.6 months. The reported results showed a statistically significant improvement in CMT with statistically insignificant visual acuity improvement. These patients had a long duration of DME before the switch, so the chronic edema may have affected the visual outcome. Furthermore, the short follow-up duration (4.6 months) may have prevented the detection of significant visual improvement. In our study, the visual improvement reached a statistically significant level at the 5-month follow-up point.
Another retrospective study [15] included 21 patients with persistent DME after ranibizumab or bevacizumab injections. Patients received three aflibercept injections and the duration of follow-up was 5 months. Their results showed statistically significant anatomic and functional improvement.
One prospective study [16] of 14 patients reported 1-month outcome of a single aflibercept injection for DME refractory to ranibizumab or bevacizumab. Their results showed that 11 patients (79%) had statistically significant CMT improvement. Visual acuity improved in 3 patients (21%) after a single aflibercept injection.
Our results support the important role of aflibercept in patients with DME who are refractory to bevacizumab injections. A statistically significant improvement in CMT was detected starting from the 2 nd month of follow-up, while statistically significant visual improvement started from the 5 th follow-up month. This means that functional improvement lags behind anatomic improvement, so studies with short follow-up duration will not probably detect significant visual gain.
The ideal time for switching from bevacizumab to aflibercept is a matter of debate. Proponents of early switching argue that chronic edema can cause irreversible photoreceptor damage. [11] Protocol I analysis showed that patients with less response after three injections had a poor response at the end of 3 years. [24] Others say that some DME patients are late responders, improving after a long period of treatment. [11] Analysis from the RISE and RIDE studies reported that patients with a poor initial response after three injections achieved the same final visual acuity as those with a good initial response. [25] In this study, the time of conversion to aflibercept was after 6 monthly bevacizumab injections. This was considered an intermediate period of treatment that allows achievement of the best possible outcome.
At the end of 1 year of follow-up, complete resolution of DME was detected in 59.4% of patients, with 64.9% having 6/12 or better visual acuity. This is a good anatomic and functional outcome in this group of refractory cases. Rahimy et al. [17] reported 24% resolution of edema at the end of 4.6 months of follow-up. It seems that continuing the treatment produces additional benefit in most patients. DME is a multifactorial disease; we do not expect all patients to respond to anti-VEGFs.
There was a short washout period between bevacizumab and aflibercept injections (only 1 month); we thought that delaying the treatment may affect the chances of patients' improvement. Thus, a carryover effect of bevacizumab cannot be excluded. In the VIVID and VISTA studies, the washout period was 3 months. This long period of treatment delay caused the edema to increase leading to worse baseline characteristics with exaggeration of the treatment benefit. [13]  One of our patients (2.7%) showed mild central macular thinning of 197 and 194 μm at the months 11 and 12, respectively. This patient had improved visual acuity and this thinning was not associated with loss of visual function. One study [26] evaluated the frequency of central retinal thickness below 200 μm in patients treated for DME. They detected macular thinning in 16% of the included patients with no affection of visual acuity. They concluded that central macular thinning below 200 μm does not seem to be affect visual function in patients treated for DME.
In this study, there was no fluctuation in the CMT after switching from monthly to bimonthly aflibercept injections. It seems that aflibercept has a long duration of action covering the 2-month duration, especially after the 5 monthly injection loading dose.

Conclusion
This study aimed to address the group of patients with persistent DME after monthly bevacizumab injections. Switching to aflibercept with a fixed regimen produced significant anatomic and functional benefits in this commonly encountered group of DME patients.
The limitations of this study include the small number of patients and the absence of a control group. Randomized prospective clinical trials comparing treatment regimens for refractory DME will be useful to further support our results.

Financial support and sponsorship
Nil.