Tirzepatide in Type 1 Diabetes: Phase 2 Trial Readout

Key Takeaways

• Tirzepatide was associated with greater short-term weight loss than placebo in adults with type 1 diabetes and obesity.
• HbA1c and total daily insulin dose also declined relative to placebo during the 12-week comparison.
• No significant adverse events were reported in either group during the reported follow-up.

In a 12-week phase 2 randomized, double-blind, placebo-controlled trial, adults with type 1 diabetes and obesity had a mean weight change of -10.3 kg with once-weekly tirzepatide versus -0.7 kg with placebo. HbA1c and total daily insulin dose also moved favorably relative to placebo during the 12-week comparison. The study enrolled adults with type 1 diabetes and a BMI greater than 30 kg/m2. Change in body weight at 12 weeks was the prespecified primary outcome.

This phase 2 trial used double-blind, placebo-controlled methods over 12 weeks in adults with type 1 diabetes and BMI >30 kg/m2. Twenty-four adults were enrolled, and 22 of 24 completed the planned 12-week assessment. Participants received once-weekly subcutaneous tirzepatide 2.5 mg for 4 weeks, then 5.0 mg for 8 weeks, or placebo. Change in body weight at 12 weeks was the prespecified primary endpoint for the between-group comparison.

For the primary outcome, the estimated treatment difference in body weight was -8.7 kg, with a 95% CI of -12.0 to -5.5. The between-group comparison reached statistical significance at 12 weeks, with P < 0.0001. Investigators also reported 8.8% weight loss with tirzepatide, with at least 5% loss in 100% versus 9% and at least 10% loss in 45% versus 0%. These findings were consistent with greater weight loss with tirzepatide at 12 weeks.

Secondary outcomes also favored tirzepatide, with an HbA1c mean difference versus placebo of -0.4% at 12 weeks. The reported 95% CI was -0.7 to 0.0, and the P value was 0.05. Total daily insulin dose changed by -24.2 units/day with tirzepatide versus -0.3 units/day with placebo, a difference from baseline versus placebo of -35.1%. The 95% CI for that insulin-dose difference was -46.5 to -21.3, with P = 0.0002 in the 12-week comparison.

No significant adverse events were reported in either group over 12 weeks. The authors concluded that tirzepatide was superior to placebo for weight loss over that period. Reported outcomes focused on body weight, HbA1c, insulin use, and adverse events in 24 enrolled adults, 22 of whom completed treatment through 12 weeks. The findings reflect short-term outcomes over the reported 12-week follow-up.