Cardiovascular safety and efficacy of metformin-SGLT2i versus metformin-sulfonylureas in type 2 diabetes: systematic review and meta-analysis of randomized controlled trials

Diabetes is a serious threat to global health and among the top 10 causes of death, with nearly half a billion people living with it worldwide. Treating patients with diabetes tend to become more challenging due to the progressive nature of the disease. The role and benefits of combination therapies for the management of type 2 diabetes are well-documented, while the comparative safety and efficacy among the different combination options have not been elucidated. We aimed to systematically synthesize the evidence on the comparative cardiovascular safety and efficacy of combination therapy with metformin-sodium-glucose cotransporter-2 inhibitors versus metformin-sulfonylureas in patients with type 2 diabetes. We searched MEDLINE-PubMed, Embase, Cochrane Library, and ClinicalTrials.gov up to 15 August 2019 without restriction in the year of publication. We included randomized controlled trials of patients with type 2 diabetes who were on metformin-sodium-glucose cotransporter-2 inhibitors or metformin-sulphonylureas combination therapy at least for a year. The primary endpoints were all-cause mortality and serious adverse events, and the secondary endpoints were cardiovascular mortality, non-fatal myocardial infarction, non-fatal stroke, hypoglycemia, and changes in glycated hemoglobin A1c (HbA1c), body weight, fasting plasma glucose, blood pressure, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol. We used a random-effects meta-analysis model to estimate mean differences for continuous outcomes and risk ratio for dichotomous outcomes. We followed PICOS description model for defining eligibility and the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015 guidelines for reporting results. Of 3,190 citations, we included nine trials involving 10,974 participants. The pooled analysis showed no significant difference in all-cause mortality (risk ration [RR] = 0.93, 95% CI [0.52, 1.67]), serious adverse events (RR = 0.96, 95% CI [0.79, 1.17]) and adverse events (RR = 1.00, 95% CI [0.99, 1.02]) between the two, but in hypoglycemia (RR = 0.13, 95% CI [0.10, 0.17], P < 0.001). Participants taking metformin-sodium glucose cotransporter-2 inhibitors showed a significantly greater reduction in HbA1c (mean difference [MD] = − 0.10%, 95% CI [− 0.17, − 0.03], body weight (MD = − 4.57 kg, 95% CI [− 4.74, − 4.39], systolic blood pressure (MD = − 4.77 mmHg, 95% CI [− 5.39, − 4.16]), diastolic blood pressure (MD = − 2.07 mmHg, 95% CI [− 2.74, − 1.40], and fasting plasma glucose (MD = − 0.55 mmol/L, 95% CI [− 0.69, − 0.41]), p < 0.001. Combination therapy of metformin and sodium-glucose cotransporter-2 inhibitors is a safe and efficacious alternative to combination therapy of metformin and sulphonylureas for patients with type 2 diabetes who are at risk of cardiovascular comorbidity. However, there remains a need for additional long-term randomized controlled trials as available studies are very limited and heterogeneous.


Scientific Reports
| (2021) 11:137 | https://doi.org/10.1038/s41598-020-80603-8 www.nature.com/scientificreports/ formin-SGLT2Is versus metformin-sulfonylureas combination therapies for patients with T2DM. We included RCTs without restriction on year of publication, but published in English language, up to 15 August 2019. The RCTs were needed to have at least a 1-year follow-up of patients. The keywords we used in different combinations using Boolean Operators were: metformin, biguanide, sodium-glucose co-transporter-2 inhibitors, SGLT-2 inhibitors, dapagliflozin, canagliflozin, empagliflozin, ertugliflozin, sulfonylurea, gliclazide, glimepiride, glyburide, glibenclamide, glipizide, tolbutamide, type 2 diabetes mellitus, T2DM, cardiovascular outcomes, and randomized controlled trials (Supplementary file 1). All potentially eligible studies were considered for this review, irrespective of the primary outcomes. Manual searching was performed to find out additional eligible trials from the reference lists of key articles.
Eligibility. We formulated the study's eligibility criteria using the PICOS (participants, interventions, comparison, outcomes, and study designs) description model 44 : • Participants • Patients with T2DM • Man or woman of any age • Who was taking a combination therapy of metformin-sulfonylurea or metformin-SGLT2Is • Intervention • A combination of metformin with any of the SGLT2Is, which could be dapagliflozin, canagliflozin, empagliflozin, or ertugliflozin.

• Comparator
• A combination of metformin with any of sulfonylureas compounds, which could be gliclazide, glipizide, glyburide, glibenclamide, or glimepiride. • Outcomes • Primary endpoints -All-cause mortality -Serious adverse events (SAEs). Study selection. Two independent authors examined the title and abstract of all searched studies. From the title and abstract of all studies identified by the database search, those studies duplicated and not meet the inclusion criteria were excluded. The full texts of the remaining studies were further reviewed. Disagreements were resolved by consensus and if persisted, we arbitrated through discussion with a third author. Data extraction. Two independent authors extracted the needed data from each RCTs. These include name of the first author, year of publication, trial registration, mean age of the participant, baseline average body weight, HbA1c, interventions, comparators, number of participants randomized, duration of follow-up, and patient-important outcomes. Data on the mean change of HbA1c (%), body weight (Kg), FPG (mmol/L), SBP (mmHg), DBP (mmHg), HDL-C (mmol/L), and LDL-C (mmol/L) were collected from baseline for continuous outcomes. The status and number of events were captured for the two groups, which include, death, hypoglycemia, adverse events (AEs), SAEs, SAEs related to study drugs, genital mycotic infection (GMI), and adverse cardiovascular events. www.nature.com/scientificreports/ Assessment of risk of bias. We used the Cochrane risk of bias tool 45 to assess the risk of bias in each included study and the risks were judged by two independent authors as "Low", "Unclear", or "High" based on the critical domains, including random sequence generation, allocation concealment, blinding, incomplete outcome data, and selective reporting. Disagreements were resolved by consensus and if persisted, we arbitrated through discussion with a third author.

Statistical analysis.
We carried out meta-analysis using the computer software packages RevMan 5.3 46 to compare the cardiovascular safety and efficacy between the two combination therapies. Pooled results of continuous patient-important outcomes i.e., HbA1c, FPG, blood pressure, body weight, HDL-C, and LDL-C were reported using a mean difference (MD) with 95% confidence interval (CI). Pooled results of binary outcomes i.e. all-cause mortality, AEs, AEs related to study drug, SAEs, SAEs related to study drug, hypoglycemic event, worsening of coronary artery disease, acute myocardial infarction (AMI), aortic aneurism, coronary artery occlusion (CAO) and GMI were summarized using risk ratio (RR) with 95% CI. We used Mantel-Haenszel method 47 to pool effect estimates of dichotomous outcomes and inverse variance for continuous outcomes. The analysis was conducted using a random-effects meta-analyses model as it assumes the observed estimates of the treatment can vary across studies because of the real differences in the treatment effect in each study as well as sampling variability (chance) 48 . We used Cochrane Q test 49 to assess heterogeneity between studies, and I 2 testing 50 to quantify heterogeneity between studies, with values > 50% representing moderate-to-high heterogeneity. We carried out sensitivity and subgroup analysis by duration of the RCTs. We couldn't conduct funnel plot and Egger test to check any possible reporting bias because the number of studies included in the meta-analyses are insufficient (less than 10 trials). We considered statistical analysis with a p-value < 0.05 statistically significant.

Results
Search results. We searched a total of 3,190 citations through the databases, of which we assessed 30 fulltext studies for eligibility and found nine of them 51-59 fulfilled the inclusion criteria. We excluded the rest 21 full-text articles 23,24,60-78 mainly for they did not include SGLT2Is or sulfonylureas as a combination therapy; included a combination of more than two glucose-lowering drugs; included single glucose-lowering drug; data were driven from review or post hoc analysis of previous RCTs; had no active comparator; or had a duration of interventions less than a year (Fig. 1). Table 1 summarizes the characteristics of the nine RCTs included. Four RCTs 51,54,56,59 used two different doses of SGLT2Is. The meta-analysis included all results of both doses for dichotomous outcomes but only a high dose of SGLT2Is for continuous outcomes.  who were in either of the two combination therapies at least for a year (Table 1).

Methodological quality and risk of bias.
The studies were found to be "low risk of bias" when these studies were subjected to the Cochrane Collaboration's Tool for Quality Assessment of Randomized Controlled Trials (Fig. 2).
Efficacy and safety assessments. All-cause mortality. All the nine included RCTs involving 10,974 participants assessed all-cause mortality/death events between intervention and control groups. Our meta-analysis of pooled results revealed no significant difference in all-cause mortality/death events between patients with T2DM who were on metformin-SGIT2Is and metformin-sulphonylureas combination therapies (RR = 0.93, 95% CI [0.52, 1.67], p = 0.81), with statistically non-significant heterogeneity between studies (I 2 = 9%) (Fig. 3). Subgroup analysis by duration of follow-up showed no significant difference in risk of death between the two groups, year 1 (RR = 0. 66  Two trials 51,56 assessed the change in HDL-C and LDL-C levels from baseline between the two arms. Both HDL-C and LDL-C levels were reduced in patients who received metformin-sulphonylureas combination therapies. However, the pooled effect was not statistically significant between the two arms in HDL-C (MD = 4.32, 95% CI [− 4.00, 12.64] mmol/L, p = 0.32), I 2 = 99%) and LDL-C (MD = 3.63, 95% CI [− 3.96, 11.22] mmol/L, P = 0.35, I 2 = 88%) (S14 & S15) respectively.
Adverse events. With pooled data from the nine trials, we found no statistically significant difference in the risk of developing adverse events between the two arms (RR = 1.00, 95% CI [0.99, 1.02], p = 0.66, I 2 = 0% (Fig. 6). We performed a sensitivity analysis by removing the highest weighted study 52  Five trials assessed the risk of serious adverse events related to study drug. The pooled result of these trials showed that serious adverse events related to study drug were less frequent on patients taking metforminsulphonylureas combination, but the pooled result was not significant at 95% CI (RR = 1.34 [0.75, 2.36] (S7).
Hypoglycemic events. We analyzed hypoglycemic events on pooled results of the nine trials involving 10,794 T2DM patients, considering the occurrence of at least one hypoglycemic event during the follow-up period. Patients under metformin-SGIT2I combination therapy were found to experience significantly fewer hypoglycemic events as compared to patients under metformin-sulphonylureas combination therapy (RR = 0.13, 95% CI [0.10, 0.17], P < 0.001) I 2 = 67%, p = 0.002) (Fig. 8). We performed sensitivity analysis by removing two low weighted trials 58,59 . However, the result of the remaining trials was similar to the nine trials in risk of hypoglycemia (RR = 0.13, 95% CI [0.10, 0.18, P < 0.001) with increased between study heterogeneity (I 2 = 73%, P = 0.009). To see the robustness of the result, we did subgroup analysis at different duration of follow-up. However, the risk of experiencing hypoglycemic events was consistently more frequent under patients on metformin-sulfonylureas combination therapy at 95% CI RR = 0. 12  Bodyweight. All trials included in the meta-analysis assessed the change in body weight from baseline between the two groups. The pooled result showed that body weight of patients in the metformin-SGLT2I was significantly reduced from baseline compared to patients in the metformin-sulfonylureas (MD = − 4.57, 95% CI  (Fig. 10). We conducted a sensitivity analysis by removing the low weighted 56

Discussion
The result of this systematic review and meta-analysis showed that the risk of all-cause mortality/death events was not statistically significant between patients in the metformin-SGLT2I and metformin-sulfonylureas combination therapies. In agreement with our findings, a previous study reported a non-significant difference in all-cause mortality and cardiovascular death between the two arms 40 . Similarly, study 77 also revealed a lower and statistically nonsignificant cardiovascular death and all-cause mortality in T2DM patients who were on metformin-sulfonylurea combination therapy. However, another study 29 reported that the use of sulfonylureas as a second-line drug has significantly associated with an increased risk of myocardial infarction and all-cause mortality.   www.nature.com/scientificreports/ The goal of durable glycemic control is to reduce the long-term risk of diabetes-related cardiovascular morbidity and mortality 57 . Recent studies showed that SGLT2Is have been shown to decrease cardiovascular events in treating high-risk patients with T2DM 34 . Likewise, the addition of empagliflozin to metformin therapy improves in patients with established CVD or heart failure 78 . Even though the current meta-analysis of metformin-SGLT2I combination showed a favorable effect on cardiovascular outcomes (acute myocardial infarction, aortic aneurism, coronary artery occlusion, and atherosclerosis), the pooled analysis was not statistically significant.
Lowering blood pressure is significantly important to reduce the risk of CVD and death in many patients with T2DM. A 10-mmHg reduction in systolic blood pressure decreased the risk of major CVD events by 20% 79 . SGLT2Is induced a greater reduction in systolic and diastolic blood pressure 73 . Similar with the other findings, the pooled result of our study showed a reduction in both systolic and diastolic blood pressure with patients in the metformin-SGLT2Is combination therapy as compared with metformin-sulfonylureas, which might be due to the effect of SGLT2Is reducing renal glucose reabsorption and increasing urinary excretion 51 . Consistent with  www.nature.com/scientificreports/ our findings, previous studies reported a greater increase from baseline in HDL-C and LDL-C in patients who were on SGLT2Is groups as compared with sulfonylureas 51,54,56 .
The result of this meta-analysis showed that the overall incidence of AEs was similar across the two arms, which is consistent with a trial reported by elsewhere 59 . However, metformin-SGLT2Is combination was associated with a higher episode of GMI which is similar to other meta-analysis reported an increased risk of GMI with SGLT2Is 73 . In addition, for both genders, the proportion of patients reporting symptoms of GMI was higher in the SGLT2Is group than in the sulfonylureas 58 . However, these infections respond to standard antimicrobial treatment and their incidence declines with time 57 . SAEs such as ketoacidosis, bone fractures, and pyelonephritis Figure 10. Comparison of change in body weight (Kg) from baseline between patients who were on metformin-SGIT2I and metformin-sulphonylureas combination therapies. SD standard deviation; CI confidence interval; MD = mean difference; Met metformin; SGLT2I sodium-glucose co-transporter 2 inhibitor; SU sulfonylurea. Figure 11. Comparison of change in FPG (mmol/L) from baseline between patients who were on metformin-SGIT2I and metformin-sulphonylureas combination therapies. SD standard deviation; CI confidence interval; MD mean difference; Met metformin; SGLT2I sodium-glucose co-transporter 2 inhibitor; SU sulfonylurea. www.nature.com/scientificreports/ were rarely reported with metformin-SGLT2Is 53 , while the pooled result of the current study did not find a statistically significant difference between metformin-SGLT2I and metformin-sulfonylureas combinations. Even though the pooled analysis did not find statistically significant results, AEs related to study drug was observed more in patients with metformin-SGLT2Is, but more SAEs related to study drug in metformin-sulfonylureas. This might be due to the hypoglycemic effect of sulfonylureas and GMI as a result of SGLT2Is respectively. Sulfonylureas as second-line drugs are associated with an increased risk of severe hypoglycemia 79 , and our study is in support of this. The hypoglycemic effect of sulfonylureas might be due to its insulin-dependent mechanism of action, while the less hypoglycemic effect of SGLT2Is is due to the non-insulin dependent mechanism of action.
Obesity is one of the main risk factors for T2DM and representing a major worldwide health problem. Lowering body weight is an important part of T2DM management. SGLT2Is has been associated with an added benefit of weight loss in patients with T2DM, whereas sulfonylureas are reported to increase body weight 80 . In support of this evidence, our study showed a 4.57 kg weight loss in metformin-SGLT2Is group than the metformin-sulfonylureas. The weight loss caused by SGLT2Is is probably due to the loss of calories via urine and glucose-induced osmotic diuresis 51 .
Long term glycemic control is the major goal of diabetes management to prevent both microvascular and macrovascular complications of DM 81 . Both metformin-SGLT2Is and metformin-sulfonylureas combinations are effective to control HbA1c for a short duration of follow-up. However, for a long duration of follow-up, metformin-SGLT2Is are more effective than metformin-sulfonylureas 73 . Our finding is consistent with this evidence where both groups were equally effective for a one-year duration of follow-up; however, as the duration of follow-up increases to 4 years, metformin-SGLT2Is combination showed a significant reduction from baseline in HbA1c. Eight previously conducted trials reported a higher reduction of FPG in patients randomized to metformin-SGLT2Is 51-54,56-59 , and our pooled result is in support of their finding as it showed reduction of FPG under patients on metformin-SGLT2Is.
This study reported important information about cardiovascular safety, efficacy, and cardiovascular risk factors control between the two combination therapies. However, we acknowledge that available studies are very limited and heterogeneous. There remains a need for additional long-term trials comparing the overall safety, efficacy, and cost-effectiveness of metformin-SGLT2Is and metformin-sulfonylureas combination therapies.

Conclusion
Combination therapy of metformin and sodium-glucose cotransporter-2 inhibitors are a safe and efficacious alternative to combination therapy of metformin and sulfonylureas for patients with T2DM who are at risk of cardiovascular comorbidity. However, there remains a need for additional long-term randomized controlled trials as available studies are very limited and heterogeneous. www.nature.com/scientificreports/ Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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