The New England Journal of Medicine AUGUST 05, 2021

Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes

Juan P. Frías, et al.

Bottom Line

In this phase 3 trial, the dual GIP and GLP-1 receptor agonist tirzepatide demonstrated superior glycemic control and weight reduction compared to the GLP-1 receptor agonist semaglutide in patients with type 2 diabetes.

Key Findings

1. At 40 weeks, HbA1c reductions were greater with tirzepatide compared to semaglutide: -2.01%, -2.24%, and -2.30% for 5 mg, 10 mg, and 15 mg doses respectively, versus -1.86% for semaglutide 1 mg (P<0.05 for all comparisons).

2. Weight loss was significantly greater with all doses of tirzepatide compared to semaglutide, with estimated mean differences of -1.9 kg, -3.6 kg, and -5.5 kg for the 5 mg, 10 mg, and 15 mg groups, respectively (P<0.001 for all).

3. The safety profiles were generally similar, with gastrointestinal events (nausea, diarrhea, and vomiting) being the most common adverse events in both tirzepatide and semaglutide arms.

4. Hypoglycemia (blood glucose <54 mg/dL) was rare in all groups, reported in 0.6%, 0.2%, and 1.7% of the tirzepatide groups and 0.4% of the semaglutide group.

Study Design

Design

RCT

Open-Label

Sample

1,879

Patients

Duration

40 wk

Median

Setting

International, multicenter

Population Adults with type 2 diabetes inadequately controlled with metformin (≥1500 mg/day).

Intervention Once-weekly subcutaneous tirzepatide (5 mg, 10 mg, or 15 mg).

Comparator Once-weekly subcutaneous semaglutide (1 mg).

Outcome Mean change from baseline in glycated hemoglobin (HbA1c) level at week 40.

Study Limitations

• The trial was open-label, which may introduce observer bias, particularly regarding the reporting of subjective adverse events.

• The duration of 40 weeks limits the ability to assess long-term durability of glycemic effect or long-term cardiovascular outcomes.

• The population lacked diverse representation across various racial and ethnic groups, potentially limiting the generalizability of results.

• The study only compared tirzepatide to the 1 mg dose of semaglutide, which is no longer the highest available dose in all markets.

Clinical Significance

The SURPASS-2 trial represents a landmark shift in diabetes management, establishing that dual incretin agonism (GIP/GLP-1) can provide superior glycemic and weight-loss efficacy compared to selective GLP-1 receptor agonism alone. These results provide clinicians with a more potent therapeutic option for patients with type 2 diabetes inadequately controlled on metformin.

Historical Context

Historically, GLP-1 receptor agonists have been the standard-of-care for injectable, non-insulin therapies in type 2 diabetes. SURPASS-2 was one of the first major head-to-head trials to introduce a dual-agonist molecule, marking a departure from the single-receptor agonist paradigm and setting a new benchmark for glycemic targets and weight management in clinical endocrinology.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

How does the 'twincretin' mechanism of tirzepatide provide a theoretical advantage over selective GLP-1 receptor agonists like semaglutide in the management of type 2 diabetes?

Key Response

Tirzepatide is a dual agonist at both the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors. While GLP-1 agonists stimulate insulin and suppress glucagon, GIP adds a synergistic insulinotropic effect and may uniquely influence lipid metabolism and energy expenditure in adipose tissue, potentially leading to the superior weight loss and glycemic control observed in the SURPASS-2 trial.

Resident

In the context of the SURPASS-2 trial results, how should a clinician manage the transition of a patient from semaglutide to tirzepatide if the patient has achieved moderate glycemic control but requires further weight reduction?

Key Response

SURPASS-2 showed dose-dependent superiority of tirzepatide (5mg, 10mg, 15mg) over semaglutide 1mg in HbA1c and weight reduction. When transitioning, clinicians must consider the 'washout' period or direct switch protocols; typically, starting at the lowest dose of tirzepatide (2.5mg) is recommended to mitigate gastrointestinal side effects, even if the patient was on a higher dose of a different GLP-1 RA, as the dual agonism increases the potency of the metabolic response.

Fellow

The SURPASS-2 trial demonstrated that a high percentage of patients achieved an HbA1c of <5.7%. What are the clinical implications of reaching 'normoglycemia' in type 2 diabetes with tirzepatide versus the traditional goal of <7.0%?

Key Response

SURPASS-2 found that up to 51% of patients in the 15mg tirzepatide group reached an HbA1c <5.7%, a level considered normal. This suggests a potential shift from 'management' to 'remission' or 'disease modification.' However, fellows must weigh the benefits of intensive metabolic control against the lack of long-term cardiovascular outcome data (at the time of the study) specifically for tirzepatide compared to the proven CV benefits of semaglutide.

Attending

How does the magnitude of weight loss observed with tirzepatide in SURPASS-2 (up to 13.1% at 40 weeks) redefine the treatment algorithm for type 2 diabetes in patients with comorbid obesity?

Key Response

The degree of weight loss seen with tirzepatide approaches that of some bariatric procedures. This evidence pushes the 'weight-centric' model of diabetes management to the forefront, suggesting that for patients with obesity, tirzepatide may be preferred over other agents to address the root cause of insulin resistance, potentially delaying the need for insulin or multiple oral agents more effectively than selective GLP-1 RAs.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Evaluate the use of the 'efficacy estimand' versus the 'treatment-policy estimand' in the SURPASS-2 trial; how does the choice of primary statistical analysis influence the interpretation of the drug’s biological potency versus its clinical effectiveness?

Key Response

The efficacy estimand (analyzing patients while on treatment without rescue therapy) demonstrates tirzepatide's maximal biological potential, which showed significant superiority. The treatment-policy estimand, however, includes data regardless of adherence or rescue therapy, providing a more conservative 'real-world' estimate. Understanding this distinction is critical for interpreting the effect size, especially since GI-related discontinuations were higher in the tirzepatide arms.

Journal Editor

A critical reviewer might argue that the SURPASS-2 trial's choice of semaglutide 1.0 mg as the comparator—instead of the 2.0 mg dose—biases the 'superiority' claim. How should this dose selection impact the editorial assessment of the study's impact?

Key Response

At the time of trial design, 1.0 mg was the standard high dose of semaglutide. However, the subsequent approval of 2.0 mg semaglutide (SUSTAIN FORTE) means tirzepatide 15 mg was compared to a sub-maximal dose of its class rival. An editor would flag this as a limitation in the 'strength' of the superiority claim, requiring the authors to contextualize whether the efficacy gap would likely persist if the maximum doses of both drugs were compared.

Guideline Committee

Based on the SURPASS-2 data, should the ADA Standards of Care be updated to prioritize tirzepatide over GLP-1 RAs for glycemic control, and what 'Level of Evidence' should be assigned to this recommendation?

Key Response

SURPASS-2 provides Level 1 evidence (large-scale randomized head-to-head trial) for the superiority of tirzepatide in HbA1c reduction. Current ADA guidelines (2023/2024) already list tirzepatide as having 'very high' glycemic and weight loss efficacy. However, the committee must balance this with the 'Evidence of Benefit' for ASCVD/CKD, where semaglutide has more established long-term trial data (e.g., SUSTAIN-6, FLOW), often leading to a 'Grade A' recommendation for both but with nuances based on the patient's primary risk profile.

Clinical Landscape

Noteworthy Related Trials

2016

SUSTAIN-6 Trial

n = 3,297 · NEJM

Tested

Semaglutide 0.5 mg or 1.0 mg weekly

Population

T2DM patients at high cardiovascular risk

Comparator

Placebo

Endpoint

Time to first occurrence of 3-point MACE

Key result: Semaglutide demonstrated a significant reduction in the risk of cardiovascular events compared to placebo.

2016

LEADER Trial

n = 9,340 · NEJM

Tested

Liraglutide 1.8 mg daily

Population

T2DM patients with high cardiovascular risk

Comparator

Placebo

Endpoint

Time to first occurrence of 3-point MACE

Key result: Liraglutide significantly lowered the rate of first occurrence of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke.

2019

REWIND Trial

n = 9,901 · Lancet

Tested

Dulaglutide 1.5 mg weekly

Population

T2DM patients with cardiovascular risk factors

Comparator

Placebo

Endpoint

Time to first occurrence of 3-point MACE

Key result: Dulaglutide significantly reduced the composite outcome of non-fatal stroke, non-fatal myocardial infarction, or cardiovascular death.

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