What Outcome and Interaction Fields Should a Stack Tracker Capture When Combining Tirzepatide with Eloralintide in 2026?
A stack tracker for the tirzepatide plus eloralintide combination must capture fields across five categories: per-compound pharmacokinetic exposure, dual-pathway satiety outcome markers, GI tolerability signals, dose-arm interaction metadata, and evidence-tier flags. The EloraTZP Phase 2b readout (EASD 2026) provides the first controlled co-administration reference dataset but leaves lean-mass, cardiovascular, and long-term maintenance fields as evidence voids.
Which Pharmacokinetic Fields Must the Tracker Capture for Each Compound Independently?
Because tirzepatide carries a ~5-day half-life (Schneck et al., PMC10962491) and eloralintide carries a ~14-day half-life (Bhattachar et al., PMC12992164), the tracker must store each compound's half-life, weekly dose, injection timestamp, and calculated trough concentration as separate fields. Conflating both into a single exposure record makes it impossible to attribute a tolerability event to the correct compound.
The ~14-day half-life of eloralintide means that a single missed weekly injection does not produce a true trough — residual exposure remains above 50% of steady-state for approximately 10 days. A tracker that flags a missed dose as a zero-exposure event will misclassify the pharmacokinetic state. The field should store a calculated residual-exposure estimate, not a binary present/absent flag.
Tirzepatide's median Tmax of approximately 24 hours post-injection (FDA NDA 215866) and eloralintide's slower subcutaneous absorption profile create a brief post-injection window where tirzepatide is rising toward peak while eloralintide remains on its flat steady-state plateau. The tracker should record injection day and time for both compounds to allow overlap-zone calculation.
The overlap zone is the period when both compounds exceed 50% of their respective peak concentrations simultaneously. This window carries the highest risk of additive GI motility suppression. Storing injection timestamps enables the tracker to flag this window automatically rather than requiring manual annotation.
| Field Name | Compound | Data Type | Source / Basis | Interaction Class |
|---|---|---|---|---|
| dose_mg | tirzepatide |
Numeric (2.5–15 mg) | FDA NDA 215866; SURMOUNT-1 | Co-Administration Data |
| dose_mg | eloralintide |
Numeric (1–9 mg) | Billings et al., 2025; EloraTZP Phase 2b | Co-Administration Data |
| injection_timestamp | Both | ISO 8601 datetime | PK overlap-zone calculation | Co-Administration Data |
| half_life_days | tirzepatide |
Numeric (~5 days) | Schneck et al., PMC10962491 | Co-Administration Data |
| half_life_days | eloralintide |
Numeric (~14 days) | Bhattachar et al., PMC12992164 | Co-Administration Data |
| residual_exposure_pct | eloralintide |
Calculated float (0–100%) | Derived from half-life and last injection timestamp | Co-Administration Data |
| titration_step | Both | Integer (step 1–N) | EloraTZP Phase 2b dose-escalation schedule | Co-Administration Data |
| overlap_zone_flag | Both | Boolean | Derived from both injection timestamps + Tmax values | Co-Administration Data |
What Dual-Pathway Satiety Outcome Fields Should the Tracker Store?
Tirzepatide suppresses appetite through GLP-1R and GIPR signalling in the hypothalamic arcuate nucleus, while eloralintide activates AMY1R in the area postrema and nucleus tractus solitarius to generate a vagal-afferent satiety signal during meals (Briere et al., PMC12640043). Because these are anatomically distinct circuits, the tracker must store pathway-specific outcome proxies for each — not a single composite satiety score.
For the incretin axis (tirzepatide), the relevant outcome fields are: inter-meal hunger score (0–10 VAS), meal initiation frequency per day, and weekly body-weight delta. These capture the between-meal appetite suppression that GLP-1R and GIPR agonism primarily drives.
For the amylin axis (eloralintide), the relevant outcome fields are: meal-size estimate (kcal per eating episode), time-to-satiety rating per meal (0–10 VAS), and eating-episode duration in minutes. These capture the within-meal satiety acceleration that AMY1R activation in the brainstem drives.
A composite weekly body-weight delta field is required as the primary outcome anchor. The EloraTZP Phase 2b trial used percent body-weight change from baseline as its primary endpoint, so the tracker's weight field must store both absolute kg and percent-from-baseline to allow direct comparison against the trial's reference arms.
Which GI Tolerability Fields Are Non-Negotiable for This Combination?
Both compounds independently slow gastric motility through distinct receptor mechanisms. Tirzepatide acts via GLP-1R-mediated vagal efferent suppression and eloralintide acts via amylin-receptor-driven gastric emptying delay. The EloraTZP highest-dose arm reported nausea in nearly half of participants and vomiting in roughly one in four (Medscape 2026) making structured GI fields non-negotiable for this stack.
Mandatory GI fields include nausea severity (0–10 NRS), vomiting episode count per 24 hours, diarrhea episode count per 24 hours, and a constipation severity score. Each field must be timestamped and linked to the injection record. This linkage enables the tracker to calculate time-to-onset from the most recent dose of each compound.
A dose-escalation phase flag is a critical structural field. The EloraTZP discontinuation data showed that GI events clustered during the escalation window rather than at stable dosing. The tracker must store a binary is_escalation_week field so that GI events can be stratified by protocol phase rather than pooled across the entire run.
An adverse-event discontinuation flag is the single most important tolerability outcome field for this stack. This boolean captures whether the user paused or stopped either compound due to a GI event. Across EloraTZP arms the discontinuation rate ranged from approximately 11 to 27 percent (Lilly/EASD 2026) which is the primary safety signal this combination carries.
What Glycemic and Metabolic Outcome Fields Does the Dual-Pathway Design Require?
The EloraTZP Phase 2b trial reported HbA1c reduction as a co-primary endpoint: up to 2.9% in the highest arm versus 2.4% for tirzepatide 15 mg alone (Lilly/EASD 2026). A stack tracker must store HbA1c at baseline and each interval, fasting glucose, and postprandial glucose as separate fields to isolate the amylin component's glucagon-suppression contribution from the incretin component's insulin-sensitisation effect.
Amylin receptor agonism suppresses postprandial glucagon secretion independently of the GLP-1R pathway. This means the postprandial glucose field captures a signal that is at least partially attributable to eloralintide alone, making it a pathway-discriminating field rather than a composite metabolic marker.
Fasting insulin and HOMA-IR are secondary metabolic fields worth capturing if the user has access to periodic lab draws. These fields allow the tracker to distinguish insulin-sensitisation effects (primarily tirzepatide-driven) from glucagon-suppression effects (partially eloralintide-driven) over the protocol run.
What Interaction-Specific Metadata Fields Must the Tracker Store?
Because the EloraTZP Phase 2b data are dose-finding rather than confirmatory, the tracker must store the specific dose-arm configuration as a structured field. The four arms tested fixed eloralintide/tirzepatide ratios (3/5, 3/10, 6/15, 9/15 mg), and outcome differences between arms are material. A tracker storing only total weekly dose cannot reconstruct which arm a user's protocol most closely resembles.
An interaction class field must be stored at the stack level, not the compound level. For this combination the current class is Co-Administration Data, reflecting the Phase 2b controlled trial. The field should be versioned so that a future Phase 3 readout can update the class without overwriting the historical record.
A lean-mass evidence-void flag is a forward-fill field the tracker should store now. The EloraTZP Phase 2b press release did not report DEXA-derived lean-mass data. Until Phase 3 data are published, any lean-mass figure in a user's tracker for this combination is extrapolated from tirzepatide monotherapy DEXA sub-studies (SURMOUNT-1: approximately 74 to 75% of weight lost as fat mass).
A cardiovascular outcomes placeholder field prevents the tracker from implying cardiovascular benefit by omission. Tirzepatide has SUMMIT trial cardiovascular data in HFpEF; eloralintide has none. The combination has neither, and the tracker must represent this asymmetry explicitly.
How Should the Tracker Represent Evidence Tier and Data Maturity for This Stack?
The EloraTZP combination holds a Co-Administration Data interaction class as of 2026, but carries four active limitations: Phase 2b only, no data beyond 48 weeks, no lean-mass DEXA sub-study, and no cardiovascular outcomes. The tracker must store these as discrete boolean flags so each void can be updated independently when new evidence emerges.
A data-maturity score — a simple integer from 1 to 5 representing the number of evidence domains with controlled data — is a useful summary field. For EloraTZP in 2026, the score is 2 out of 5: weight loss and glycemic control have Phase 2b controlled data; lean mass, cardiovascular outcomes, and long-term maintenance do not.
A next-evidence-event field — storing the anticipated Phase 3 readout timeline — gives the tracker a forward-looking anchor. Lilly has announced a Phase 3 programme for EloraTZP. When Phase 3 data are published, the tracker should prompt a full field-set review rather than only updating the weight-loss figure. What Does 2026 Research Show About Tirzepatide's Clinical Efficacy and Safety in Metabolic Diseases Beyond Diabetes and Obesity? What Are the Evidence-Based Dosing Protocols for Retatrutide in the TRIUMPH Phase 3 Trial Versus Tirzepatide in 2026? Does Tirzepatide Produce Meaningfully Greater Weight Loss Than Semaglutide — and Is the Serious Adverse Event Rate Higher in 2026?