Escalate or Switch? Treating the Post-Titration GLP-1 Non-Responder: A Target Trial Emulation With Dose-Equivalence Reclassification
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Background
When a GLP-1 patient stops responding, should the clinician push the dose or change the drug? Observational answers conflate two distinct sources of confounding. Most early-week “escalations” in real-world data are FDA-mandated titration steps rather than deliberate clinical decisions, and patients who deviate do so for reasons we cannot observe. Semaglutide and tirzepatide are also not equivalent milligram-for-milligram, so naive class-switch comparisons mix mechanism and dose. We resolve both by restricting to post-titration patients and reclassifying treatments under the Whitley 2023 dose-equivalence framework. 1
Methods
From 68,969 telehealth GLP-1 patients we built a post-titration cohort. Each patient’s index time is the day they completed at least four weeks at therapeutic dose (Whitley tier 3 or higher: semaglutide 1.0 mg or tirzepatide 5 mg). Confirmed slow response is less than 5% total weight loss at the index, consistent with the categorical-response framing used in FDA weight-management drug-development guidance and AACE/ACE criteria. 7,8 We compared four post-index strategies against continuing the current regimen: within-class dose escalation, equipotent class switch (a Whitley tier change of 1 or fewer), and class switch with potency increase. Direction-specific analyses split switches into semaglutide-to-tirzepatide and tirzepatide-to-semaglutide arms. Outcomes were percent weight loss at 12 and 24 weeks post-index. We estimated effects six ways: propensity-score matching; IPTW with linear and gradient-boosted propensities; the g-formula with linear and gradient-boosted outcome models; and AIPW, the doubly-robust estimator we use as the tiebreaker. 2,4 Two-layer inverse probability of censoring weighting addressed strategy adherence and outcome ascertainment. 2,4 We computed E-values, ran a negative-control specification, and stratified by tolerability. 3 As a sensitivity, we re-defined slow response using a held-out-fold prognostic threshold from the companion paper.
Results
The post-titration cohort comprised 24,876 confirmed slow responders. Within-class dose escalation produced a small consistent benefit at 24 weeks: AIPW +0.64 pp (95% CI +0.16 to +1.12), with five non-AIPW estimators ranging +0.47 to +0.76 pp. The continue arm itself lost an additional 8.07 pp over the same window (96% continued to lose), so escalation is a marginal addition to a substantial natural slope, not a rescue. Equipotent class switching from semaglutide to tirzepatide was inconclusive: linear and matching estimators ranged +1.26 to +1.80 pp, but AIPW was −0.33 pp (95% CI −1.27 to +0.60) with only 90 treated patients (the equipotent sema → tirz arm with a 24-week outcome) and limited propensity-score overlap. Class switch with simultaneous potency increase (sema → tirz) gave AIPW +0.65 pp at 12 weeks (95% CI +0.37 to +0.92, n = 80, the switch + escalation sema → tirz arm with a 12-week outcome). A negative-control specification yielded ATE −0.13 pp, indicating the pipeline did not generate spurious signal under random allocation (a plumbing check, not a test of confounding). A held-out-fold prognostic-threshold sensitivity gave a null effect (+0.04 pp), correcting an earlier circular +1.06 pp estimate.
Conclusions
Among confirmed post-titration slow responders, within-class dose escalation adds approximately 0.6 percentage points at 24 weeks on top of an 8 percentage point natural slope, consistently across six estimators including doubly-robust inference. This headline effect is small and not robust to modest unmeasured confounding (E-value 1.27) or to MNAR-style outcome attrition (tipping point δ ≈ 1.2 pp), so it should be read as hypothesis-generating rather than practice-changing. Class-switching evidence is inconclusive; linear-estimator results suggesting benefit did not survive doubly-robust estimation in small treated samples with limited propensity overlap. The dose-ladder framework, with phase-specific evidence grading, is hypothesis-generating and, given the small effect and heavy censoring, insufficient on its own to change practice.
