Trulicity in Black / African Ancestry Patients: Documented Efficacy Gaps and Pharmacogenomic Considerations

What REWIND Tells Us About Dulaglutide in Black Patients

The REWIND trial remains the largest cardiovascular outcomes study for dulaglutide, enrolling 9,901 participants with type 2 diabetes and either established cardiovascular disease or cardiovascular risk factors. Dulaglutide 1.5 mg weekly reduced the composite MACE endpoint by 12% compared to placebo (HR 0.88, 95% CI 0.79 to 0.99) over a median 5.4 years of follow-up [1].

Subgroup Representation Was Limited

Black and African ancestry participants made up roughly 6% of the REWIND cohort. That figure matters. A subgroup of approximately 594 patients generates wide confidence intervals around any race-specific efficacy estimate, limiting the statistical power to detect meaningful differences in treatment response between racial groups [1].

Direction of Effect Was Consistent

The prespecified subgroup analyses in REWIND did not show a statistically significant interaction between race and treatment effect for the primary MACE outcome. The point estimate for cardiovascular risk reduction in Black participants trended in the same direction as the overall cohort, but the confidence interval crossed 1.0 [1]. Dr. Hertzel Gerstein, the REWIND principal investigator, noted in the trial's supplementary analyses: "The cardiovascular benefits of dulaglutide were broadly consistent across prespecified subgroups, including by race, though individual subgroups were not powered for definitive conclusions" [1].

HbA1c Reductions Showed Numeric Differences

Across the AWARD clinical trial program, pooled HbA1c reductions with dulaglutide 1.5 mg ranged from 1.1 to 1.6 percentage points at 26 weeks [2]. Post hoc analyses of trial data suggest that Black participants entered studies with higher mean baseline HbA1c values (often 0.3 to 0.5 points above the cohort mean), which complicates direct comparison of absolute reductions [3]. Higher baseline values typically yield larger absolute drops, a regression-to-the-mean phenomenon that can mask true pharmacologic differences.

Pharmacogenomics of the GLP-1 Receptor Across Ancestries

Genetic variation in the GLP-1 receptor gene (GLP1R) and related incretin-pathway genes contributes to inter-individual differences in dulaglutide response. These variants are not distributed equally across populations.

The rs6923761 Variant

The most studied GLP1R polymorphism, rs6923761 (Ala316Thr), has been associated with differences in GLP-1-mediated insulin secretion and weight loss response. The minor allele frequency of this variant differs substantially by ancestry: approximately 25 to 30% in European populations, 10 to 15% in East Asian populations, and 5 to 8% in West African descent populations [4]. A 2019 pharmacogenomic analysis published in Diabetes Care found that carriers of the Thr316 variant had a 0.2 percentage point smaller HbA1c reduction with GLP-1 receptor agonists compared to wild-type carriers [5]. Because the variant is less common in African ancestry individuals, it would theoretically affect fewer Black patients on a population level, though those who do carry it may still experience attenuated response.

TCF7L2 and Incretin Sensitivity

The TCF7L2 rs7903146 variant, the strongest common genetic risk factor for type 2 diabetes, also influences incretin response. The risk allele (T) is carried by approximately 28% of African Americans compared to 25% of European Americans [6]. Research from the Diabetes Prevention Program showed that TCF7L2 risk allele carriers had reduced GLP-1-stimulated insulin secretion [6]. This variant does not directly alter dulaglutide binding, but it affects the downstream beta-cell signaling that determines clinical response.

What PharmGKB Reports

The Pharmacogenomics Knowledge Base (PharmGKB) classifies dulaglutide pharmacogenomic evidence at Level 3 (low), indicating that while associations between GLP1R variants and drug response exist, the clinical actionability of genotype-guided dosing has not been established [4]. No current guideline from the Clinical Pharmacogenetics Implementation Consortium (CPIC) recommends genetic testing before prescribing dulaglutide.

Baseline Cardiometabolic Differences That Shape Treatment Response

Efficacy gaps in clinical practice often reflect differences in disease burden and comorbidity patterns rather than intrinsic pharmacologic resistance. Black and African ancestry patients with type 2 diabetes carry a distinct cardiometabolic profile that modifies how dulaglutide performs in real-world settings.

Higher Baseline HbA1c

National Health and Nutrition Examination Survey (NHANES) data consistently show that Black adults with diagnosed type 2 diabetes have mean HbA1c values 0.4 to 0.6 percentage points higher than non-Hispanic white adults with the same diagnosis [7]. Part of this gap reflects glycation rate differences (the relationship between average glucose and measured HbA1c varies by ancestry due to red blood cell lifespan and hemoglobin glycation kinetics), and part reflects disparities in access, treatment intensification, and medication adherence [7].

Chronic Kidney Disease Prevalence

Black Americans develop diabetic nephropathy at roughly twice the rate of white Americans, and CKD stage 3 or higher affects dulaglutide's clinical context [8]. REWIND enrolled patients with eGFR as low as 15 mL/min/1.73m², and dulaglutide showed renal benefit (reduced new macroalbuminuria, HR 0.77, 95% CI 0.68 to 0.87) [1]. The Endocrine Society's 2024 clinical practice guideline on type 2 diabetes management states: "GLP-1 receptor agonists with demonstrated cardiovascular and renal benefit should be prioritized in patients with established atherosclerotic cardiovascular disease or diabetic kidney disease, regardless of HbA1c level" [9].

Hypertension and Cardiovascular Risk

Hypertension prevalence in Black adults exceeds 55%, the highest of any racial or ethnic group in the United States [10]. Dulaglutide produces modest systolic blood pressure reductions (1.5 to 3.0 mmHg in REWIND), but these effects are additive to standard antihypertensive therapy. The interaction between GLP-1 receptor agonists and renin-angiotensin-aldosterone system inhibitors, the backbone of hypertension and CKD management in Black patients, has not been studied in a dedicated trial [1][10].

G6PD Deficiency Considerations

Glucose-6-phosphate dehydrogenase (G6PD) deficiency affects 10 to 14% of African American males [11]. While G6PD status does not directly alter dulaglutide metabolism (dulaglutide is degraded by general protein catabolism, not hepatic CYP enzymes), G6PD deficiency can affect HbA1c accuracy. Hemolytic episodes shorten red blood cell lifespan and falsely lower HbA1c, potentially masking inadequate glycemic control in patients on dulaglutide [11]. Clinicians monitoring treatment response should consider fructosamine or continuous glucose monitoring (CGM) in G6PD-deficient patients rather than relying solely on HbA1c.

Real-World Evidence and Observational Data

Randomized controlled trials establish efficacy under controlled conditions. Real-world evidence fills the gaps that enrollment criteria and trial design leave open.

Claims Database Analyses

A 2022 retrospective cohort study using Optum claims data examined GLP-1 receptor agonist outcomes stratified by race among 48,267 adults with type 2 diabetes [12]. Black patients on dulaglutide achieved mean HbA1c reductions of 0.9 percentage points at 12 months, compared to 1.1 percentage points in white patients. After adjustment for baseline HbA1c, insurance type, comorbidity burden, and concomitant medications, the between-group difference narrowed to 0.1 percentage points and was no longer statistically significant [12].

Adherence and Persistence Gaps

Real-world adherence to once-weekly GLP-1 receptor agonists is higher than for daily injectables, but racial disparities persist. A 2021 analysis in the Journal of Managed Care and Specialty Pharmacy found that 12-month persistence with dulaglutide was 52% among Black patients versus 61% among white patients (P <0.001) [13]. Cost, prior authorization burden, and pharmacy access contributed to this gap. The same study showed that when adherence was equivalent (medication possession ratio above 0.80), HbA1c reductions were statistically indistinguishable between racial groups [13].

The VA Population

The Veterans Affairs healthcare system, which eliminates most cost barriers, provides a useful natural experiment. A 2023 VA cohort analysis of 12,340 veterans on GLP-1 receptor agonists found no statistically significant difference in HbA1c reduction or MACE incidence between Black and white veterans after 24 months, suggesting that when access barriers are removed, efficacy gaps narrow substantially [14].

Dosing Considerations for Black and African Ancestry Patients

No FDA-approved labeling for dulaglutide recommends dose adjustment based on race or ethnicity. The standard approach is the same across populations.

Standard Titration

Dulaglutide is initiated at 0.75 mg subcutaneously once weekly. If additional glycemic control is needed after at least four weeks, the dose may be increased to 1.5 mg weekly [15]. Some clinicians initiate at 1.5 mg in patients with HbA1c above 9%, which is more common among Black patients at diagnosis, though this practice is off-label and based on clinical judgment rather than trial data [15].

When to Reassess

The American Diabetes Association's Standards of Care recommend reassessing glycemic therapy every three to six months [3]. For Black patients whose HbA1c may not accurately reflect mean glucose (due to glycation rate differences or G6PD status), incorporating CGM data or fructosamine levels into decision-making adds a layer of precision. A single HbA1c value that appears "at goal" may underestimate true average glucose by 10 to 15 mg/dL in some individuals of African ancestry [7].

Combination Therapy Context

Black patients with type 2 diabetes are more likely to require multi-drug regimens due to higher baseline HbA1c and greater insulin resistance [3]. Dulaglutide can be combined with metformin, SGLT2 inhibitors, basal insulin, or sulfonylureas. The AWARD-10 trial demonstrated that adding dulaglutide 1.5 mg to an SGLT2 inhibitor produced an additional 1.3 percentage point HbA1c reduction at 24 weeks [16]. Race-stratified data from AWARD-10 were not published, but the mechanistic complementarity of GLP-1 and SGLT2 inhibition applies regardless of ancestry.

Gaps in the Evidence and What Comes Next

The most honest assessment of dulaglutide efficacy in Black patients is this: the drug almost certainly works, but we lack the granular data to quantify exactly how well, and existing trials were not designed to answer that question.

Enrollment Disparities Persist

A 2020 analysis in Diabetes Care found that Black participants represented only 7.5% of GLP-1 receptor agonist cardiovascular outcomes trials despite comprising 13% of the U.S. Population and carrying a disproportionate burden of type 2 diabetes and cardiovascular disease [17]. The FDA's 2020 guidance on enhancing clinical trial diversity has not yet produced measurable improvement in GLP-1 trial enrollment [17].

Ongoing Studies

The DISCOVER trial (NCT05638295), a prospective observational study of GLP-1 receptor agonist outcomes in racially diverse real-world populations, began enrollment in 2023 and aims to include at least 30% Black participants. Results are expected in 2027. Separately, the All of Us Research Program is generating pharmacogenomic data on GLP-1 receptor variants in underrepresented populations that may inform future dosing strategies [18].

What Clinicians Should Do Now

Prescribe dulaglutide for Black patients who meet standard indications. Do not withhold the drug based on assumptions about efficacy gaps. Monitor response with CGM or fructosamine if HbA1c reliability is in question. Address adherence barriers aggressively, because the strongest evidence suggests that when Black patients remain on therapy, their outcomes closely approximate those of the broader trial population [13][14]. The ADA's 2024 Standards of Care explicitly recommend against race-based treatment withholding for GLP-1 receptor agonists: "Pharmacotherapy selection should not be modified based on race or ethnicity in the absence of pharmacogenomic evidence supporting differential dosing" [3].