Original Research

Assessment of Glucagon-like Peptide-1 Receptor Agonists in Veterans TakingBasal/Bolus Insulin Regimens

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Background: Clinical use of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) is well established as add-on therapy to oral medications and basal insulin. However, there is little published data regarding the use of GLP-1 RAs for longer than 12 months in patients taking basal/bolus insulin regimens. The primary goal of our study was to assess the long-term efficacy of GLP-1 RAs as add-on therapy to basal/bolus insulin regimens.

Methods: This study was a retrospective record review of all patients on basal/bolus insulin regimens who received additional therapy with a GLP-1 RA. The primary outcome was the change in glycosylated hemoglobin A 1c (HbA 1c ) at 3, 6, 12, 18, and 24 months after initiation of the GLP-1 RA. Secondary outcomes included change in weight and total daily dose (TDD) of insulin and incidence of hypoglycemia and other adverse effects (AEs).

Results: Ninety-two patient records were reviewed. Mean glycemic control changed from baseline −1.1% (95% CI, −1.3 to −0.8; P < .001) at 3 months; −1.0% (95% CI, −1.3 to −0.7; P < .001) at 6 months; −0.9% (95% CI, 1.3 to −0.6; P < .001) at 12 months; −0.9% (95% CI, −1.4 to −0.3; P = .002) at 18 months; and −0.7 (95% CI, −1.4 to 0.1; P = .07) at 24 months. A significant decrease in weight was also observed from baseline through 18 months, and a significant decrease in TDD of insulin was identified from baseline through 12 months. Hypoglycemia was documented in 29.8% of patients at any point during GLP-1 RA therapy, and gastrointestinal AEs were documented in 18.3% of patients.

Conclusions: Adding GLP-1 RAs to complex insulin regimens may help achieve glycemic control while decreasing insulin requirements and mitigating undesirable AEs, such as weight gain.



In 2019, diabetes mellitus (DM) was the seventh leading cause of death in the United States, and currently, about 11% of the American population has a DM diagnosis.1 Most have a diagnosis of type 2 diabetes (T2DM), which has a strong genetic predisposition, and the risk of developing T2DM increases with age, obesity, and lack of physical activity.1,2 Nearly one-quarter of veterans have a diagnosis of DM, and DM is the leading cause of comorbidities, such as blindness, end-stage renal disease, and amputation for patients receiving care from the Veterans Health Administration (VHA).2 The elevated incidence of DM in the veteran population is attributed to a variety of factors, including exposure to herbicides, such as Agent Orange, advanced age, increased risk of obesity, and limited access to high-quality food.3

After diagnosis, both the American Diabetes Association (ADA) and the American Association of Clinical Endocrinologists and American College of Endocrinology (AACE/ACE) emphasize the appropriate use of lifestyle management and pharmacologic therapy for DM care. The use of pharmacologic agents (oral medications, insulin, or noninsulin injectables) is often determined by efficacy, cost, potential adverse effects (AEs), and patient factors and comorbidities.4,5

The initial recommendation for pharmacologic treatment for T2DM differs slightly between expert guidelines. The ADA and AACE/ACE recommend any of the following as initial monotherapy, listed in order to represent a hierarchy of usage: metformin, glucagon-like peptide-1 receptor agonists (GLP-1 RAs), sodium-glucose cotransporter 2 (SGLT-2) inhibitors, or dipeptidyl peptidase-4 (DPP-4) inhibitors, with the first 3 agents carrying the strongest recommendations.4,5 For patients with established atherosclerotic cardiovascular disease (CVD), chronic kidney disease, or heart failure, it is recommended to start a long-acting GLP-1 RA or SGLT-2 inhibitor. For patients with T2DM and hemoglobin A1c (HbA1c) between 7.5% and 9.0% at diagnosis, the AACE/ACE recommend initiation of dual therapy using metformin alongside another first-line agent and recommend the addition of another antidiabetic agent if glycemic goals are not met after regular follow-up. AACE/ACE recommend the consideration of insulin therapy in symptomatic patients with HbA1c > 9.0%.5 In contrast, the ADA recommends metformin as first-line therapy for all patients with T2DM and recommends dual therapy using metformin and another preferred agent (selection based on comorbidities) when HbA1c is 1.5% to 2% above target. The ADA recommends the consideration of insulin with HbA1c > 10% or with evidence of ongoing catabolism or symptoms of hyperglycemia.4 There are several reasons why insulin may be initiated prior to GLP-1 RAs, including profound hyperglycemia at time of diagnosis or implementation of insulin agents prior to commercial availability of GLP-1 RA.

GLP-1 RAs are analogs of the hormone incretin, which increases glucose-dependent insulin secretion, decreases postprandial glucagon secretion, increases satiety, and slows gastric emptying.6,7 When used in combination with noninsulin agents, GLP-1 RAs have demonstrated HbA1c reductions of 0.5% to 1.5%.8 The use of GLP-1 RAs with basal insulin also has been studied extensively.6,8-10 When the combination of GLP-1 RAs and basal insulin was compared with basal/bolus insulin regimens, the use of the GLP-1 RAs resulted in lower HbA1c levels and lower incidence of hypoglycemia.6,9 Data have demonstrated the complementary mechanisms of using basal insulin and GLP 1 RAs in decreasing HbA1c levels, insulin requirements, and weight compared with using basal insulin monotherapy and basal/bolus combinations.6,9-13 Moreover, 3 GLP-1 RA medications currently on the market (liraglutide, dulaglutide, and semaglutide) have displayed cardiovascular and renal benefits, further supporting the use of these medications.2,5

Despite these benefits, GLP-1 RAs may have bothersome AEs and are associated with a high cost.6 In addition, some studies have found that as the length of therapy increases, the positive effects of these agents may diminish.9,11 In one study, which looked at the impact of the addition of exenatide to patients taking basal or basal/bolus insulin regimens, mean changes in weight were −2.4 kg at 0 to 6 months, −4.3 kg at 6 to 12 months, −6.2 kg at 12 to 18 months, and −5.5 kg at 18 to 27 months. After 18 months, an increase in weight was observed, but the increase remained lower than baseline.11 Another study, conducted over 12 months, found no significant decrease in weight or total daily dose (TDD) of insulin when exenatide or liraglutide were added to various insulin regimens (basal or basal/bolus).13 To date, minimal published data exist regarding the addition of newer GLP-1 RAs and the long-term use of these agents beyond 12 months in patients taking basal/bolus insulin regimens. The primary goal of this study was to evaluate the effect of adding GLP-1 RAs to basal/bolus insulin regimens over a 24-month period.


This study was a retrospective, electronic health record review of all patients on basal and bolus insulin regimens who received additional therapy with a GLP-1 RA at Veteran Health Indiana in Indianapolis from September 1, 2015, to June 30, 2019. Patients meeting inclusion criteria served as their own control. The primary outcome was change in HbA1c at 3, 6, 12, 18, and 24 months after initiation of the GLP-1 RA. Secondary outcomes included change in weight and TDD of insulin at 3, 6, 12, 18, and 24 months after the initiation of the GLP-1 RAs and incidence of patient-reported or laboratory-confirmed hypoglycemia and other AEs.

Patients were included if they were aged ≥ 18 years with a diagnosis of T2DM, had concomitant prescriptions for both a basal insulin (glargine, detemir, or NPH) and a bolus insulin (aspart, lispro, or regular) before receiving add-on therapy with a GLP-1 RA (exenatide, liraglutide, albiglutide, lixisenatide, dulaglutide, or semaglutide) from September 1, 2015, to June 30, 2019, and had baseline and subsequent Hb A1c measurements available in the electronic health record. Patients were excluded if they had a diagnosis of T1DM, were followed by an outside clinician for DM care, or if the GLP-1 RA was discontinued before subsequent HbA1c measurement. The study protocol was approved by the Research and Development Office of Veteran Health Indiana, and the project was deemed exempt from review by the Indiana University Institutional Review Board due to the retrospective nature of the study.

Data analysis was performed using Excel. Change from baseline for each interval was computed, and 1 sample t tests (2-tailed) compared change from baseline to no change. Due to the disparity in the number of patients with data available at each of the time intervals, a mean plot was presented for each group of patients within each interval, allowing mean changes in individual groups to be observed over time.


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