SUSTAIN Clinical Trial Program for Semaglutide
The SUSTAIN program demonstrated that once-weekly subcutaneous semaglutide significantly reduces major adverse cardiovascular events in patients with type 2 diabetes at high cardiovascular risk, with SUSTAIN-6 showing a 26% reduction in the composite endpoint of cardiovascular death, nonfatal MI, or nonfatal stroke.
Overview of the SUSTAIN Program
The SUSTAIN (Semaglutide Unabated Sustainability in Treatment of Type 2 Diabetes) clinical trial program comprises multiple phase 3 trials evaluating once-weekly subcutaneous semaglutide across the spectrum of type 2 diabetes management 1, 2. The program included:
- SUSTAIN 1-5: Glycemic efficacy trials comparing semaglutide to placebo and active comparators
- SUSTAIN 6: Cardiovascular outcomes trial (the pivotal safety/efficacy study)
- SUSTAIN 7: Head-to-head comparison with dulaglutide
- Additional Japanese trials and ongoing phase 3b studies
SUSTAIN-6: The Cardiovascular Outcomes Trial
Study Design and Population
SUSTAIN-6 was a multi-center, double-blind, placebo-controlled trial that randomized 3,297 patients with type 2 diabetes and high cardiovascular risk to receive once-weekly semaglutide (0.5 mg or 1.0 mg) or placebo for a minimum of 2 years 3, 4, 5, 6.
Key baseline characteristics:
- Mean age: 65 years (61% male)
- Mean diabetes duration: 13.9 years
- Mean BMI: 33 kg/m²
- 83% had established atherosclerotic cardiovascular disease, chronic kidney disease, or both 6
- 58.8% had established CVD without CKD
- 10.7% had CKD only
- 13.4% had both CVD and CKD
- 17% had cardiovascular risk factors alone 5
Specific high-risk criteria included:
- Age ≥50 years with established stable cardiovascular, cerebrovascular, or peripheral artery disease, chronic kidney disease, or NYHA class II-III heart failure
- Age ≥60 years with other specified cardiovascular risk factors 5
Primary Cardiovascular Outcomes
The primary endpoint was time to first occurrence of 3-point MACE (cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke). The trial was designed to test noninferiority with a margin of 1.8 for the upper boundary of the 95% CI 3, 6.
Results demonstrated superiority, not just noninferiority:
- Primary MACE occurred in 6.6% (108/1,648) with semaglutide vs. 8.9% (146/1,649) with placebo
- Hazard ratio: 0.74 (95% CI 0.58-0.95; P<0.001 for noninferiority) 3, 4, 5, 6
- This represents a 26% relative risk reduction in major cardiovascular events
Individual MACE Components
Breaking down the composite endpoint 5, 6:
- Nonfatal MI: 2.9% vs. 3.9% (HR 0.74; 95% CI 0.51-1.08; P=0.12)
- Nonfatal stroke: 1.6% vs. 2.7% (HR 0.61; 95% CI 0.38-0.99; P=0.04) - statistically significant
- Cardiovascular death: 2.7% vs. 2.8% (HR 0.98; 95% CI 0.65-1.48) - no difference
The cardiovascular benefit was primarily driven by the reduction in nonfatal stroke 7.
Renal Outcomes
Semaglutide significantly reduced new or worsening nephropathy compared to placebo 6. However, there was an important safety signal:
- Rates of retinopathy complications were significantly higher with semaglutide (HR 1.76; 95% CI 1.11-2.78; P=0.02) 6
- Retinopathy complications included vitreous hemorrhage, blindness, or conditions requiring intravitreal treatment or photocoagulation
Glycemic and Weight Outcomes
While SUSTAIN-6 was primarily a cardiovascular outcomes trial, metabolic benefits were observed:
- HbA1c reduction: Semaglutide demonstrated superior glycemic control across all SUSTAIN trials 1, 2
- Body weight reduction: Consistent weight loss was observed with semaglutide treatment 1
Safety Profile
Tolerability findings:
- More patients discontinued semaglutide due to adverse events, mainly gastrointestinal 3, 4, 6
- Fewer serious adverse events occurred overall in the semaglutide group 6
- Gastrointestinal adverse events were more common in women than men, though discontinuation rates were similar between genders 8
Trial completion:
- 98.0% of patients completed the trial
- Vital status was known for 99.6% at trial end 5
Subgroup Analyses from SUSTAIN-6
Cardiovascular Risk Stratification
Post hoc analyses demonstrated consistent MACE reduction across varying baseline cardiovascular risk profiles 8:
- Patients with prior MI or stroke vs. no prior MI or stroke
- Established CVD vs. CV risk factors alone
- Hazard ratios <1.0 in all subgroups except those with prior heart failure (HR 1.06; 95% CI 0.72-1.57) 7
Important caveat: The interaction p-value for heart failure was 0.046, suggesting semaglutide may not reduce MACE in patients with established heart failure 7.
Age and Gender Effects
Cardiovascular benefits were consistent across age and gender subgroups 8, 9:
- Age subgroups: ≤60, >60 to ≤65, >65 to ≤70, and >70 years
- Both male and female patients
- HbA1c reduction was greater in younger patients (≤60 years) compared to older subgroups (p-interaction = 0.01) 9
- Body weight reduction was consistent across all age groups 9
Regulatory and Clinical Implications
FDA approval status (as of the guideline evidence):
- Initially approved for type 2 diabetes treatment 4, 10
- Subsequently approved for secondary cardiovascular risk reduction 11
- The 2018 ADA guidelines noted semaglutide "has not yet been approved by the FDA" at that time, but later guidelines confirm approval 3, 4
Guideline positioning:
- ADA/EASD consensus recommends GLP-1 receptor agonists with demonstrated cardiovascular benefit (including semaglutide) for patients with type 2 diabetes and established ASCVD or high cardiovascular risk 4, 12
- The decision to treat should be considered independently of baseline HbA1c or individualized HbA1c target 12
Comparison with Other GLP-1 Receptor Agonists
SUSTAIN-6 results were consistent with the LEADER trial (liraglutide) 3, 4, which showed:
- 13.0% vs. 14.9% MACE rate (HR 0.87; P=0.01 for superiority)
- Significant reduction in cardiovascular death (HR 0.78; P=0.007)
Key distinction: While liraglutide demonstrated cardiovascular death reduction, semaglutide in SUSTAIN-6 did not show this benefit, though the overall MACE reduction was numerically greater with semaglutide (26% vs. 13%) 3, 4.
Pooled Analysis with PIONEER-6
When SUSTAIN-6 data were pooled with PIONEER-6 (oral semaglutide trial) 7, 13:
- Overall MACE HR: 0.76 (95% CI 0.62-0.92)
- Effect primarily driven by nonfatal stroke reduction (HR 0.65; 95% CI 0.43-0.97)
- No effect on heart failure hospitalization (HR 1.03; 95% CI 0.75-1.40)
- Cardiovascular benefits were independent of body weight changes, indicating direct cardiorenal effects 13
Clinical Pearls and Caveats
Important considerations for clinical practice:
Retinopathy monitoring: Given the increased risk of retinopathy complications, patients should have baseline ophthalmologic assessment and close monitoring, particularly those with pre-existing diabetic retinopathy 6
Heart failure patients: The lack of MACE benefit in patients with prior heart failure suggests caution in this subgroup, though the drug is not contraindicated 7
Gastrointestinal tolerability: Expect higher discontinuation rates due to GI adverse events; dose titration and patient counseling are essential 6
Cardiovascular benefit mechanism: The stroke reduction appears to be the primary driver of cardiovascular benefit, not MI or cardiovascular death reduction 7
Real-world effectiveness: Recent real-world data suggest semaglutide may provide greater cardiovascular risk reduction compared to tirzepatide in patients with overweight/obesity and established ASCVD (29% reduction in rMACE-3) 14