DOI: 10.2337/dc06-0706 © 2006 by the American Diabetes Association
Efficacy and Safety of the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin Added to Ongoing Metformin Therapy in Patients With Type 2 Diabetes Inadequately Controlled With Metformin Alone
1 Centre Hospitalier Universitaire de Nantes, Nantes, France Address correspondence and reprint requests to Gary Meininger, MD, Director, Clinical Research, Merck Research Laboratories, 126 E. Lincoln Ave., RY34A-254, Rahway, NJ 07065. E-mail: gary_meininger{at}merck.com
OBJECTIVEThe efficacy and safety of the dipeptidyl peptidase-4 inhibitor, sitagliptin, added to ongoing metformin therapy, were assessed in patients with type 2 diabetes who had inadequate glycemic control (HbA1c [A1C] 7 and 10%) with metformin alone.
RESEARCH DESIGN AND METHODSAfter a screening diet/exercise run-in period, a metformin dose titration/stabilization period, and a 2-week, single-blind, placebo run-in period, 701 patients, aged 1978 years, with mild to moderate hyperglycemia (mean A1C 8.0%) receiving ongoing metformin ( RESULTSAt week 24, sitagliptin treatment led to significant reductions compared with placebo in A1C (0.65%), fasting plasma glucose, and 2-h postmeal glucose. Fasting insulin, fasting C-peptide, fasting proinsulin-to-insulin ratio, postmeal insulin and C-peptide areas under the curve (AUCs), postmeal insulin AUCtoglucose AUC ratio, homeostasis model assessment of ß-cell function, and quantitative insulin sensitivity check index were significantly improved with sitagliptin relative to placebo. A significantly greater proportion of patients achieved an A1C <7% with sitagliptin (47.0%) than with placebo (18.3%). There was no increased risk of hypoglycemia or gastrointestinal adverse experiences with sitagliptin compared with placebo. Body weight decreased similarly with sitagliptin and placebo. CONCLUSIONSSitagliptin 100 mg once-daily added to ongoing metformin therapy was efficacious and well tolerated in patients with type 2 diabetes who had inadequate glycemic control with metformin alone.
Abbreviations: AUC, area under the curve DPP-4, dipeptidyl peptidase-4 ECG, electrocardiogram FPG, fasting plasma glucose GIP, glucose-dependent insulinotropic peptide GLP-1, glucagon-like peptide-1 HOMA-ß, homeostasis model assessment of ß-cell function HOMA-IR, homeostasis model assessment of insulin resistance OHA, oral antihyperglycemic agent QUICKI, quantitative insulin sensitivity check index
Sitagliptin is an oral, once-daily, potent, and highly selective dipeptidyl peptidase-4 (DPP-4) inhibitor for the treatment of type 2 diabetes (15). DPP-4 inhibitors enhance levels of active incretin hormones, gut-derived peptides that are released into the circulation after ingestion of a meal (68). Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) account for the majority of incretin action (9). In the presence of elevated glucose concentrations, GLP-1 and GIP increase insulin release and GLP-1 lowers glucagon secretion, thereby decreasing the postmeal rise in glucose concentration and reducing fasting glucose concentrations (9). Both GLP-1 and GIP are rapidly inactivated by the enzyme DPP-4 (10,11). By blocking this inactivation, DPP-4 inhibitors increase active incretin levels, enhancing incretin effects, and thereby offer a new therapeutic approach for the management of patients with type 2 diabetes. Treatment with a single antihyperglycemic agent is often unsuccessful in achieving and/or maintaining glycemic control in patients with type 2 diabetes, and many patients require combinations of antihyperglycemic agents (12). Metformin, a biguanide, is one of the most commonly used first-line antihyperglycemic agents in the treatment of type 2 diabetes, which acts primarily by lowering hepatic glucose production and may also improve insulin resistance (12). Because sitagliptin and metformin target potentially complementary pathways, the addition of sitagliptin for patients with type 2 diabetes who do not have adequate glycemic control with metformin monotherapy may provide improved glycemic control. In an earlier, short-term study (13) of sitagliptin added to ongoing metformin therapy in patients with type 2 diabetes with inadequate glycemic control with metformin alone, a sustained 24-h reduction in glucose compared with placebo was observed after 28 days of treatment. In light of these findings, the present placebo-controlled study assessed the efficacy and safety of sitagliptin 100 mg once-daily added to ongoing metformin therapy in patients with type 2 diabetes who were inadequately controlled on metformin alone. The 100 mg once-daily dose of sitagliptin was selected based on the results of two previous, 12-week, dose-range-finding studies in patients with type 2 diabetes in which treatment at this dose produced the greatest improvement in glycemic control (4,5).
Men and women (aged 1878 years) with type 2 diabetes and inadequate glycemic control (defined by an HbA1c [A1C] level 7 and 10%) while taking metformin monotherapy at a stable dose of at least 1,500 mg/day, either at entry into the study or after a metformin dose-stable run-in period, were eligible to be randomized. Patients who were not currently taking an oral antihyperglycemic agent (OHA), were taking any OHA in monotherapy, or were taking metformin in combination with another OHA were potentially eligible to participate in the study if their A1C level met the screening criteria. Patients were excluded if they had a history of type 1 diabetes, insulin use within 8 weeks of screening, renal function impairment inconsistent with the use of metformin, or a fasting plasma glucose (FPG) (or a fasting fingerstick glucose) at, or just before, randomization >14.4 mmol/l (260 mg/dl). A history of hypoglycemia was not an exclusion criterion. Other OHAs were prohibited during the study. Concurrent lipid-lowering and antihypertensive medications, thyroid medications, hormone replacement therapy, and birth control medications were allowed but were expected to remain at stable doses.
This was a multinational, randomized, parallel-group study with a placebo-controlled, double-blind treatment period. The screening/eligibility run-in period was designed to allow patients with type 2 diabetes being treated with a variety of different regimens, as described in the prior section, to participate. Patients who were already taking metformin at a dose of at least 1,500 mg/day whose A1C level was
Study end points Safety and tolerability were assessed throughout the study. Monitoring for adverse experiences, physical examinations, vital signs, body weight, 12-lead electrocardiograms (ECGs) (read at a central reading laboratory), and safety laboratory measurements comprising routine hematology, serum chemistry, and urinalysis were performed. Investigators evaluated each clinical adverse experience for intensity (mild, moderate, or severe), duration, outcome, and relationship to study drug. Adverse experiences of special interest included hypoglycemia and gastrointestinal adverse experiences.
Statistical analysis Safety analyses were performed using the all-patients-as-treated population, which included all randomly assigned patients who received at least one dose of double-blind study therapy. For hypoglycemia as well as prespecified selected gastrointestinal adverse experiences (abdominal pain, diarrhea, nausea, and vomiting) and change in body weight, inferential testing was done to determine statistical significance levels for between-group comparisons.
Demographics and baseline characteristics The overall disposition of patients who were screened and randomly assigned in the placebo-controlled period of the study is shown in Fig. 1 of the online appendix (available at http://care.diabetesjournals.org). Of the 1,464 patients who were screened, 701 were randomly assigned to study treatment. The demographic and baseline anthropometric and disease characteristics of the randomly assigned patients were similar between the treatment groups (see Fig. 1 of the online appendix). For the entire study population, the average duration of diabetes was 6.2 years, average baseline A1C was 8% (range 6.411.0%; 55% of patients had a baseline A1C <8%), and the average baseline FPG was 9.5 mmol/l (171.5 mg/dl). A greater percentage of patients in the placebo group discontinued the study compared with patients in the sitagliptin group (19 vs. 10%) (see Fig. 1 of the online appendix). The most common reasons for discontinuation were lack of efficacy (placebo 5.5 vs. sitagliptin 1.5%), withdrawal of consent (placebo 4.2 vs. sitagliptin 2.2%), clinical adverse experiences (placebo 2.1 vs. sitagliptin 2.4%), and lost to follow-up (placebo 2.1 vs. sitagliptin 0.9%).
Efficacy
Treatment with sitagliptin 100 mg also led to a significant (P < 0.001) reduction from baseline at week 24 in FPG compared with placebo (Table 1). The placebo-subtracted least-squares mean (95% CI) reduction from baseline in FPG for the sitagliptin 100 mg group was 1.4 mmol/l (1.7 to 1.1) (25.4 mg/dl [31.0 to 19.8]). The mean reduction from baseline in FPG in the sitagliptin group was near maximal for the study by week 6, with a trend toward a progressive further decrease in FPG through the remainder of the double-blind treatment period (Fig. 1B). In contrast, there was a generally sustained mean increase from baseline in FPG levels in the placebo group from weeks 6 through 24 (Fig. 1B). In addition to the significant decreases in A1C and FPG, treatment with sitagliptin 100 mg also led to significant increases relative to placebo in fasting insulin (P < 0.050), fasting C-peptide (P < 0.010), homeostasis model assessment of ß-cell function (HOMA-ß) (P < 0.001), and quantitative insulin sensitivity check index (QUICKI) (P < 0.050) and a significant decrease in fasting proinsulin-to-insulin ratio (P < 0.010) at week 24 (Table 1). Sitagliptin 100 mg had no significant effect on fasting proinsulin levels or homeostasis model assessment of insulin resistance (HOMA-IR) (see Table 1 of the online appendix). Treatment with sitagliptin 100 mg led to a significant decrease in 2-h postmeal glucose (P < 0.001) (see Table 1 of the online appendix and Fig. 1C) and significant increases in 2-h postmeal insulin (P < 0.050) (see Table 1 of the online appendix) and 2-h postmeal C-peptide (P < 0.001) relative to placebo at week 24 (see Table 1 of the online appendix). Treatment with sitagliptin also led to a significant decrease in 2-h postmeal glucose total AUC (P < 0.001) and significant increases in 2-h postmeal insulin total AUC (P < 0.010), 2-h postmeal C-peptide AUC (P < 0.001), and 2-h postmeal insulin-to-glucose AUC ratio (P < 0.001) relative to placebo at week 24 (see Table 1 of the online appendix). A significantly smaller proportion of patients in the sitagliptin group required glycemic rescue therapy during the 24-week study compared with the placebo group (21 of 464 patients [4.5%] receiving sitagliptin required rescue therapy during the study compared with 32 of 237 patients [13.5%] in the placebo group; P < 0.001). Additionally, the time to initiation of rescue therapy was significantly (P < 0.001) later in the sitagliptin group than in the placebo group. Treatment with sitagliptin 100 mg led to statistically significant, albeit generally small, decreases in total cholesterol, triglycerides, non-HDL cholesterol, and triglyceride-to-HDL cholesterol ratio, as well as a small, statistically significant, increase in HDL cholesterol relative to placebo at week 24. However, no significant between-group difference in LDL cholesterol was observed (placebo-subtracted least-squares mean [95% CI] percent changes from baseline at week 24: total cholesterol 2.8% [5.3 to 0.4]; triglycerides 16.9% [24.3 to 9.4]; HDL cholesterol 2.0% [0.04.0]; non-HDL cholesterol 4.8% [8.3 to 1.3]; triglyceride-to-HDL cholesterol ratio 19.4% [27.9 to 10.8]; LDL cholesterol 0.8% [5.4 to 3.8]) (see Table 1 of the online appendix).
Safety
For most specific clinical adverse experiences, the incidences were generally similar in the sitagliptin and placebo groups. Only a few adverse experiences occurred at a higher incidence with sitagliptin compared with placebo, and for these, which included nasopharyngitis, urinary tract infection, arthralgia, back pain, and cough, the differences were generally small (see Table 2 of the online appendix). The incidence of other adverse experiences classified by body system, including the incidence of cardiac-related adverse experiences, infections, and musculoskeletal adverse experiences, was generally comparable between the two treatment groups.
There were no laboratory adverse experiences that had a notably greater incidence in the sitagliptin group compared with the placebo group (see Table 2 of the online appendix). No meaningful differences between treatment groups were observed in mean changes from baseline or in the occurrence of elevations in alanine aminotransferase or aspartate aminotransferase. A small mean increase ( There were no clinically meaningful changes in ECGs or vital signs with sitagliptin treatment. Small (0.60.7 kg), but statistically significant (P < 0.05), mean decreases from baseline in body weight were observed in both treatment groups; however, the mean between-group difference was not significant (P = 0.835 for between-group comparison for change from baseline at Week 24).
In this study, sitagliptin 100 mg once-daily provided statistically significant and clinically meaningful reductions in A1C compared with placebo when added to ongoing metformin therapy in patients with type 2 diabetes and mild to moderate hyperglycemia who had inadequate glycemic control with metformin monotherapy. Secondary glycemic end points including FPG and 2-h postmeal glucose also showed clinically important and statistically significant improvements with sitagliptin 100 mg compared with placebo. The A1C- and FPG-lowering responses to sitagliptin treatment were sustained during the 24-week treatment period, with a trend of continuing reductions in both end points throughout the treatment period. Nearly half of the patients receiving sitagliptin 100 mg once-daily achieved the current American Diabetes Association glycemic goal of A1C <7% (14) compared with less than one-fifth of placebo-treated patients. Consistent with its mechanism of action, treatment with sitagliptin 100 mg led to a statistically significant increase compared with placebo in HOMA-ß, a surrogate end point that has been used to assess the ability of pancreatic ß-cells to secrete insulin under fasting conditions. In addition, improvement in the fasting proinsulin-to-insulin ratio, consistent with improved ß-cell function, was also observed with sitagliptin treatment. Preclinical studies have shown that GLP-1 can stimulate ß-cell differentiation and proliferation; additionally, GLP-1 has been shown to inhibit apoptosis of ß-cells, including that of human ß-cells in vitro (8,9). Moreover, DPP-4 inhibitors have been shown to stimulate ß-cell neogenesis and survival in streptozotocin-treated rats (15). The implications of such effects of DPP-4 inhibition on ß-cell mass and function in humans still need to be determined with additional clinical studies. End points reflecting changes in insulin sensitivity (QUICKI and HOMA-IR) showed a mixed response with a small, but statistically significant, increase in QUICKI and no significant change in HOMA-IR. During this study, patients underwent a standard 2-h meal tolerance test, enabling an assessment of the effect of treatment on postmeal glucose, insulin, and C-peptide concentrations and the ratio of insulin to glucose. Treatment with sitagliptin led to clinically important and statistically significant improvements in all of these end points compared with placebo. Sitagliptin 100 mg was well tolerated in this clinical trial. No clinically meaningful differences in the overall incidence of clinical adverse experiences, clinical adverse experiences leading to discontinuation, serious clinical adverse experiences, or laboratory adverse experiences were observed in the sitagliptin group compared with the placebo group. The addition of sitagliptin to ongoing metformin therapy did not lead to an increase in the incidence of gastrointestinal side effects, which are typically associated with metformin treatment alone. Sitagliptin treatment was associated with a very low incidence of hypoglycemia adverse experiences, with a rate similar to that seen in the placebo group. Furthermore, none of the hypoglycemia episodes exhibited marked severity. Treatment with sitagliptin led to a small, but statistically significant, mean decrease from baseline in body weight, with no significant difference in weight change compared with placebo. Sitagliptin treatment also led to slight, statistically significant improvements in lipid parameters. No clinically meaningful differences were observed in the sitagliptin group compared with placebo with respect to mean changes in serum chemistry and hematology analytes, and there were no clinically meaningful changes in vital signs or ECGs with sitagliptin treatment. In summary, in patients with type 2 diabetes who had inadequate glycemic control with metformin alone, the addition of sitagliptin 100 mg once-daily was well tolerated and provided effective and sustained improvement in A1C, FPG, and 2-h postmeal glucose, as well as significant improvements in indexes of insulin secretion and ß-cell function, including HOMA-ß and the fasting proinsulin-to-insulin ratio. Treatment with sitagliptin was associated with a low rate of hypoglycemia that was similar to that seen with placebo, as well as a neutral effect on body weight.
Funding for this study was provided by Merck Research Laboratories. The authors thank Dr. Alan G. Meehan (Merck Research Laboratories) for his contribution in writing this article. A list of author contributions regarding the work performed in this study can be found in the online appendix.
B.C. has acted as a consultant or speaker for GlaxoSmithKline, Merck, Sharpe & Dohme, Pfizer, Sanofi-Aventis, and Takeda. A.K. has acted as a consultant or speaker for Merck Research Laboratories.
* A complete list of the Study 620 investigators can be found in the online appendix at http://care.diabetesjournals.org. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C Section 1734 solely to indicate this fact. Received for publication March 31, 2006. Accepted for publication August 28, 2006.
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