Tirzepatide

Tirzepatide is a 39-amino-acid synthetic peptide with a molecular weight of 4,813.45 Da. It is a first-in-class dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist. The peptide is based on the native GIP sequence with modifications that confer GLP-1R agonist activity. A C20 fatty diacid moiety is attached via a linker at Lys20, enabling albumin binding and extended duration of action. CAS number: 2023788-19-2.

Tirzepatide activates both the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), both class B GPCRs, though with differential potency. It has approximately 5-fold greater affinity for GIPR than GLP-1R. At the GIPR, tirzepatide triggers Gs-mediated cAMP production in adipocytes and pancreatic beta cells, enhancing insulin secretion, improving fat storage efficiency in subcutaneous depots, and increasing lipid buffering capacity. At the GLP-1R, it produces the same hypothalamic satiety signaling, gastric emptying delay, and beta-cell potentiation as selective GLP-1 agonists. The dual mechanism produces additive or combined effects on energy balance -- GIPR activation in the CNS may enhance the anorectic signals from GLP-1R activation, and peripheral GIPR signaling improves adipose tissue function and lipid handling in ways GLP-1 alone does not.

The SURMOUNT-1 trial (N=2,539), published in the New England Journal of Medicine in 2022 (DOI: 10.1056/NEJMoa2206038), evaluated tirzepatide at 5mg, 10mg, and 15mg weekly doses versus placebo in adults with obesity or overweight. At 72 weeks, mean weight loss was 15.0% (5mg), 19.5% (10mg), and 22.5% (15mg) versus 3.1% with placebo. 63% of participants on the 15mg dose achieved at least 20% weight loss, compared to 1.3% on placebo. SURMOUNT-2, in participants with type 2 diabetes, showed 12.8% and 14.7% weight loss at 10mg and 15mg respectively. SURMOUNT-3, combining tirzepatide with intensive lifestyle intervention, demonstrated 26.6% total weight loss.

In the SURPASS program for type 2 diabetes, tirzepatide demonstrated A1C reductions of 2.07-2.59% across doses, with up to 97% of participants achieving A1C below 7.0%. SURPASS-2 showed tirzepatide was superior to semaglutide 1mg for both A1C reduction (2.09% vs 1.86%) and weight loss (12.4% vs 6.2%) at the 15mg dose, establishing the clinical relevance of dual-agonism over selective GLP-1 agonism.

Tirzepatide has a plasma half-life of approximately 5 days (120 hours), supporting once-weekly subcutaneous dosing. Peak plasma concentration occurs at 8-72 hours post-injection. Like semaglutide, the extended half-life is driven by albumin binding via the C20 fatty diacid chain. Tirzepatide is metabolized by proteolytic degradation and fatty acid beta-oxidation. It is not a major substrate for CYP450 enzymes. Elimination is primarily renal, with no dose adjustment required for mild to moderate renal impairment.

Lyophilized tirzepatide should be stored at -20C before reconstitution. Reconstitute with sterile bacteriostatic water by directing the stream against the vial wall and gently swirling until fully dissolved. Do not shake or vortex. Reconstituted solution should be stored at 2-8C and used within 28 days. The peptide is stable in solution at pH 6.0-7.5. Protect from direct light and avoid repeated freeze-thaw cycles. Allow refrigerated vials to reach room temperature for 15 minutes before drawing doses.

Tirzepatide is actively studied in research on dual incretin receptor pharmacology, adipose tissue biology, beta-cell preservation, NASH resolution, obstructive sleep apnea, heart failure with preserved ejection fraction (HFpEF), and polycystic kidney disease. The SURMOUNT-MMO cardiovascular outcomes trial is ongoing. Preclinical work explores GIPR signaling in bone metabolism and central appetite circuits.

In SURMOUNT-1, the most common treatment-emergent adverse events were gastrointestinal: nausea (24.6-33.3% across doses vs 9.5% placebo), diarrhea (18.7-21.2%), vomiting (5.7-12.2%), and constipation (5.8-11.5%). These were predominantly mild to moderate and occurred mainly during dose escalation. Discontinuation due to adverse events was 4.3-7.1% across tirzepatide doses versus 2.6% placebo. Serious adverse events were balanced across groups.