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Hindawi Journal of Diabetes Research Volume 2020, Article ID 6321826, 12 pages https://doi.org/10.1155/2020/6321826 Research Article Meta-Analysis of 11 Heterogeneous Studies regarding Dipeptidyl Peptidase 4 Inhibitor Add-On Therapy for Type 2 Diabetes Mellitus Patients Treated with Insulin Katsuya Shibuki ,1,2 Shuji Shimada,1 and Takao Aoyama1 1Department of Pharmacy, Tokyo University of Science, 2641 Yamazaki, Noda 278-8510, Japan 2Clinical Research Center, Medical Hospital, Tokyo Medical and Dental University, 1-5-45 Yushima, Tokyo 113-8519, Japan Correspondence should be addressed to Katsuya Shibuki; [email protected] Received 6 April 2020; Revised 24 September 2020; Accepted 22 October 2020; Published 11 November 2020 Academic Editor: Daniela Foti Copyright © 2020 Katsuya Shibuki et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Several clinical trials have addressed the therapeutic strategy of adding dipeptidyl peptidase 4 (DPP-4) inhibitors to the treatment of type 2 diabetes mellitus (DM) inadequately controlled by insulin therapy. However, there is a high degree of heterogeneity in these studies, and the cause of which has not been identified. Methods. We conducted a meta-analysis of randomized controlled trials, which compared the efficacy and safety of adding DPP-4 inhibitors or placebo to insulin therapy; the level of hemoglobin A1c (HbA1c) in the patients was >7.0%, and the duration of treatment was ≥8 weeks. We focused on the mean changes in HbA1c from the baseline (ΔHbA1c) and the incidence of hypoglycemia. We assumed that five baseline parameters (HbA1c, fasting blood glucose, body mass index (BMI), duration of type 2 DM, and duration of treatment) could affect ΔHbA1c. Regarding the incidence of hypoglycemia, we suspected that the heterogeneity was caused by differences in the definition of hypoglycemia among the studies. Results. Data obtained from 11 studies (n = 4654 patients) were included in the analysis. The mean ΔHbA1c between the DPP-4 inhibitor and placebo groups was -0.61% (95% confidence interval (CI): -0.74 to -0.48, I2 =73:4%). There was substantial heterogeneity among the 11 studies, but 74.1% of this variability was explained by the difference in BMI. The odds ratio for the incidence of hypoglycemia was 1.02 (95% CI: 0.74 to 1.42, I2 =63:8%), with substantial heterogeneity due to differences in the definition of hypoglycemia among the studies. There was no apparent effect of publication bias. Conclusions. The addition of DPP-4 inhibitors to insulin therapy for adult patients with type 2 DM can significantly reduce HbA1c levels without increasing the occurrence of hypoglycemia. BMI and hypoglycemia definition could explain the heterogeneity in the clinical trials. This trial is registered with PROSPERO #CRD42016035994. 1. Introduction GLP-1 acts on β cells and increases insulin secretion in a glucose-dependent manner. In addition, GLP-1 exerts a The control of blood glucose level is important for preventing glucose-dependent inhibitory effect on glucagon secretion. microvascular-related complications associated with type 2 Because of these effects, DPP-4 inhibitors have a low risk of diabetes mellitus (DM) treatment [1–5]. Eventually, many hypoglycemic incidence, and they are suitable as an add-on patients with type 2 DM require insulin therapy. However, therapy with insulin. a meta-analysis of randomized controlled trials reported that Several clinical trials have addressed the therapeutic 50%–65% of patients receiving insulin therapy failed to strategy of adding DPP-4 inhibitors to the treatment of type achieve their glycemic control goals [6]. 2 DM inadequately controlled by insulin therapy. In 2015, Dipeptidyl peptidase 4 (DPP-4) inhibitors are oral hypo- Chen et al. performed a meta-analysis to combine seven clin- glycemic agents that prevent the inactivation of glucagon-like ical studies and showed that DPP-4 inhibitor therapy has a peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP) low risk of hypoglycemia and that it improves glycemic con- and enhance the effects of endogenous incretin [7–10]. trol [11]. Subsequently, several investigators confirmed these 2 Journal of Diabetes Research conclusions using a meta-analysis approach on the same who had been treated with a fixed dose of insulin (insulin lis- topic [12–14]. However, there is a high degree of heterogene- pro, insulin aspart, insulin glulisine, insulin neural, insulin ity in these meta-analyses, possibly because of variations in isophane, insulin glargine, insulin detemir, or insulin deglu- the designs and patient backgrounds among the clinical tri- dec; single agent or in combination with metformin) for als, and the cause of this variability has not been identified. more than 8 weeks before DPP-4 treatment, were enrolled. This high degree of heterogeneity suggests that the effi- Randomized controlled trials of ≥12 weeks were selected for cacy of DPP-4 inhibitors differs in each population, used in the analysis. The intervention group had received an addi- individual trials. If this assumption is true, it is inappropriate tional DPP-4 inhibitor (sitagliptin, alogliptin, vildagliptin, to combine populations with different drug efficacies using a saxagliptin, linagliptin, anagliptin, or teneligliptin) at the standard meta-analysis approach. However, if the source of standard dosage coadministered with the insulin therapy. this heterogeneity is attributable to variations in other The control group had received placebo instead of a DPP-4 parameters (covariates), which characterize the population inhibitor with the insulin therapy. in each study, then it is reasonable to combine the data from individual trials using a meta-analysis approach, taking into 2.3. Study Selection and Data Extraction. Two investigators account the effects of the covariates. (K.S. and S.S.) reviewed the titles and summaries of 3003 Thus, the aim of the present study was to identify covar- publications to determine whether they should be included iates that could explain the observed variations among the in our analysis. The study design, subject data, and evaluated clinical trials. Initially, we selected several baseline parame- points in each study were summarized, and the bias in the ters that could affect the efficacy of DPP-4 inhibitors, namely, study was assessed using “the Cochrane risk of bias tool” hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), [22]. The two investigators discussed and resolved any dis- body mass index (BMI), type 2 DM duration, and treatment crepancies between them, and a consensus was reached. duration [15, 16]. We also selected the incidence of hypogly- cemia as a safety index for DPP-4 inhibitors. There are two 2.4. Data Analysis. We evaluated the mean change in HbA1c definitions of hypoglycemia, and the incidence of hypoglyce- (ΔHbA1c) and the incidence of hypoglycemia. First, we per- mia could be affected by the definition chosen [17]. There- formed a meta-analysis using a random-effects model [23]. A fore, we also tested the possibility that the differences in the random-effects model is a statistical model that assumes definition of hypoglycemia can explain the heterogeneity in random variations among studies. We used the restricted the incidence of hypoglycemia among the studies. maximum likelihood method to estimate τ, the index of variation between studies [24], and the Hartung–Knapp fi 2. Materials and Methods adjustment to calculate the con dence interval [25, 26]. We calculated the difference in ΔHbA1c between the interven- This review was conducted and reported according to the tion and control groups and the odds ratio for the incidence Preferred Reporting Items for Systematic Reviews and of hypoglycemia, with 95% confidence intervals for each. If Meta-Analyses (PRISMA) [18]. The protocol was based on no standard deviation for outcome was reported in a study, Preferred Reporting Items for Systematic Reviews and Meta- the standard error was calculated from the reported sample Analyses for Protocols 2015 (PRISMA-P 2015) [19] and was size and the 95% confidence interval. registered in the International Prospective Register of System- We defined a full analysis set as all subjects who received atic Reviews (PROSPERO, ID = CRD42016035994) [20]. a DPP-4 inhibitor or placebo at least once after randomiza- tion and whose data were available. In addition, we defined 2.1. Information Sources and Literature Search. In accor- a safety analysis set as all subjects who received a DPP-4 dance with Peer Review of Electronic Search Strategies inhibitor or placebo at least once after randomization. We (PRESS) [21], we used MEDLINE, EMBASE, the Cochrane analyzed mean ΔHbA1c based on the full analysis set data Library, ClinicalTrials.gov, and pharmaceutical company and the incidence of hypoglycemia based on the safety anal- sites as sources of information. A comprehensive literature ysis set data. We collected data that were available in pub- search was conducted from September 1, 2015, to December lished manuscripts or on websites of pharmaceutical 31, 2016. The search keywords used were as follows: “dipep- companies and trial registries. Additionally, if the data were tidyl peptidase 4 inhibitors,”“sitagliptin,”“alogliptin,” not present in the results, we contacted the corresponding “vildagliptin,”“saxagliptin,”“linagliptin,”“anagliptin,” authors or sponsors for the

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