Summary: In the 40-week SURPASS-CN-INS phase 3 trial, once-weekly tirzepatide added to basal insulin reduced HbA1c more than placebo in adults with uncontrolled type 2 diabetes in China. The estimated treatment difference was -1.48% for 10 mg and -1.45% for 15 mg versus placebo.
PICO Summary
| Element | Detail |
|---|---|
| Population | 257 adults with uncontrolled type 2 diabetes receiving insulin glargine, with or without metformin and/or an SGLT2 inhibitor, across 26 Chinese hospitals. |
| Intervention | Once-weekly tirzepatide 5, 10 or 15 mg added to basal insulin for 40 weeks. |
| Comparator | Placebo added to basal insulin for 40 weeks. |
| Outcomes | HbA1c change at week 40 was -2.39% with 10 mg and -2.37% with 15 mg versus -0.91% with placebo. Differences were -1.48% and -1.45%, respectively (both P<0.0001). Diarrhea was reported in 37% of the 10 and 15 mg groups versus 8% with placebo. |
| Study design | Double-blind, multicenter, randomized, placebo-controlled phase 3 trial. |
SURPASS-CN-INS: Tirzepatide + Basal Insulin
Phase 3 - 40 weeks - 257 patients
Adding tirzepatide to basal insulin produced substantially greater HbA1c reductions than placebo over 40 weeks in adults with uncontrolled type 2 diabetes, with mainly mild or moderate gastrointestinal events.
Expert Commentary
SURPASS-CN-INS adds a clinically familiar but important question: what happens when tirzepatide is added to basal insulin in people whose glycemia remains uncontrolled? Over 40 weeks, both 10 mg and 15 mg produced substantially greater HbA1c reductions than placebo, with placebo-adjusted differences close to 1.5 percentage points. The trial also included participants using metformin and, in some cases, an SGLT2 inhibitor, which reflects common combination practice. Gastrointestinal adverse events were mostly mild or moderate, but diarrhea, nausea and vomiting were more frequent with tirzepatide.
Can I use this with my patients? The findings support considering tirzepatide as an add-on option for adults with type 2 diabetes inadequately controlled on basal insulin, provided the regimen is individualized and locally licensed. The study was conducted in China, lasted 40 weeks, and was designed for glycemic efficacy rather than cardiovascular or renal outcomes. Insulin dose adjustment, hypoglycemia risk, gastrointestinal tolerance, nutrition, retinopathy status and the patient’s ability to manage injections remain central. The 5 mg arm was randomized, but the primary comparison emphasized 10 and 15 mg. Do not read the result as a reason to stop basal insulin abruptly or to assume that every patient will tolerate escalation. It is evidence for a structured, monitored add-on strategy.
References
Guo L, Dong X, Ma J, Liu M, Lu Y, Wang H, et al. Efficacy and safety of tirzepatide added to basal insulin in patients with type 2 diabetes in China (SURPASS-CN-INS): a double-blind, multicentre, randomised, placebo-controlled, phase 3 trial. Lancet Diabetes Endocrinol. 2025. doi:10.1016/S2213-8587(25)00248-7. PMID: 41167231. ClinicalTrials.gov: NCT05691712.