SURPASS-SWITCH subgroup analysis finds consistent benefit across patient types

A new subgroup analysis of the SURPASS-SWITCH trial reports that adults with type 2 diabetes who switched from dulaglutide (Trulicity) to tirzepatide (Mounjaro/Zepbound) saw larger drops in blood sugar and body weight than those who stayed on dulaglutide, and this held true across every prespecified group of patients studied ^[1].

SURPASS-SWITCH is a phase IV, randomized, open-label trial that enrolled adults with type 2 diabetes who had an HbA1c between 7.0% and 9.5%, had been on a stable dose of dulaglutide for at least six months, and had a body mass index of 25 or higher ^[1]. Participants were randomly split into two groups: one continued dulaglutide with escalation up to 4.5 mg or the maximum tolerated dose, and the other switched to tirzepatide with escalation up to 15 mg or the maximum tolerated dose ^[1]. Researchers then measured changes in HbA1c and body weight at 40 weeks ^[1].

The subgroup analysis broke results down by age (under 65 versus 65 and older), baseline HbA1c, how long someone had had diabetes, their starting dulaglutide dose and how long they had been on it, BMI category, ethnicity, and sex ^[1]. In every one of these groups, the reductions in both HbA1c and body weight were significant and consistently larger with tirzepatide than with dulaglutide ^[1].

The size of the HbA1c improvement varied somewhat. People who started with higher HbA1c levels and those with lower baseline BMI saw bigger HbA1c reductions after switching ^[1]. Weight-loss results also varied by group: the non-Hispanic or non-Latino subgroup saw a greater reduction in body weight than the Hispanic or Latino subgroup ^[1]. The safety profile looked similar no matter which subgroup a patient fell into, and nausea and diarrhea were the most commonly reported side effects across nearly all groups ^[1].

Why it matters for patients

Many people with type 2 diabetes who take dulaglutide eventually plateau — their blood sugar or weight numbers stop improving even at a stable, tolerated dose. This analysis suggests that switching to tirzepatide can produce further improvement across a wide range of patient profiles, including older adults, people who have had diabetes for a decade or more, and those on either the lower or higher standard dulaglutide dose ^[1]. That is useful information for patients and clinicians trying to figure out whether a treatment switch is likely to help for their particular situation, since it was tested in these specific subgroups rather than just in the trial population as a whole ^[1].

The finding that side effects were broadly similar across subgroups may also be reassuring for people wondering whether age, weight, or sex would change their risk of nausea or diarrhea after a switch, though these remained the most frequently reported issues ^[1]. It is not yet known from this analysis how these subgroup differences would apply to people with type 1 diabetes, those never treated with a GLP-1 drug before, or people using tirzepatide brand Zepbound specifically for weight management rather than diabetes, since SURPASS-SWITCH enrolled only adults with type 2 diabetes already on dulaglutide ^[1].

What happens next

The study is registered under trial number NCT05564039 ^[1]. The analysis was published by authors including employees and shareholders of Eli Lilly and Company, the maker of both dulaglutide and tirzepatide, alongside two authors who reported no conflicts of interest ^[1]. No further trial dates or regulatory actions tied to this subgroup analysis were included in the source material.