Detection and Excretion Profile of Retatrutide in Human Plasma and Urine by LC-HRMS: Implications for Antidoping Analysis.
Plasma is a more suitable matrix for detecting retatrutide than urine, with a detection window of approximately 56 days after administration.
Where it sits
this study against the rest of the retatrutide (ly3437943) corpusSummary and findings
This study measured the detection and elimination profile of retatrutide in human plasma and urine after subcutaneous administration. Four participants self-administered 2 mg on Days 1 and 7, with samples collected at predefined time points. The study found that plasma is the more suitable matrix for detection compared to urine.
Abstract
Rationale Retatrutide (LY3437943) is a novel long-acting triple incretin receptor agonist that targets the glucagon-like peptide-1 receptor (GLP-1R), glucose-dependent insulinotropic polypeptide receptor (GIPR), and glucagon receptor (GCGR). Its pronounced effects on body composition and metabolic health, combined with increasing off-label use among physically active populations, raise concerns about potential misuse in sport. Despite growing clinical interest and anecdotal reports about use among amateur athletes, information on the detection and elimination profile of retatrutide in humans remains unexplored. Methods A method based on liquid chromatography-high-resolution mass spectrometry (LC-HRMS) dedicated to monitor retatrutide was developed and validated in human plasma and urine in accordance with World Anti-Doping Agency (WADA) criteria. Detection was based on the [M + 3H]3+ precursor ion by targeted selected-ion monitoring (t-SIM), with confirmatory analysis via parallel reaction monitoring (PRM) of structurally diagnostic fragment ions. From four retatrutide users who self-administered 2 mg subcutaneously on Days 1 and 7, blood and urine samples were collected at predefined time points following self-administration. Results The method was proved fit-for-purpose regarding selectivity, reliability, robustness, and stability. Limits of detection (LOD) were evaluated using both empirical ≥ 95% detection rate criteria and sigmoidal logistic regression modeling, yielding 6.14 ng/mL in plasma and 2.44 ng/mL in urine. Neither intact retatrutide nor metabolite-derived signals were detected in urine samples throughout the entire collection period, despite systematic application of multiple extraction strategies. Plasma concentration-time profiles exhibited nonmonotonic behavior, consistent with prolonged subcutaneous absorption and depot-like release kinetics following repeated dosing. Conclusion These findings suggest that plasma represents the appropriate matrix for intact retatrutide detection compared with urine. The extended plasma detection window, approximately 56 days after the first dose, supports plasma-based testing as a suitable analytical strategy for this and related long-acting therapeutic peptides in antidoping testing context.
Background
This paper addresses the detection and elimination profile of retatrutide, a triple incretin receptor agonist, in humans. Prior to this study, there was limited information on its detection in antidoping contexts, particularly given its increasing off-label use among athletes. Understanding its pharmacokinetics is crucial for developing effective antidoping strategies.
Methods
The study utilized a liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method to monitor retatrutide in human plasma and urine, following World Anti-Doping Agency (WADA) criteria. Four participants self-administered 2 mg subcutaneously on Days 1 and 7, with blood and urine samples collected at predefined time points. The primary outcome measure was the limit of detection (LOD) in both plasma and urine.
Results
The LOD was determined to be 6.14 ng/mL in plasma and 2.44 ng/mL in urine. Plasma concentration-time profiles showed nonmonotonic behavior, indicating prolonged absorption and depot-like release kinetics. No intact retatrutide or metabolite-derived signals were detected in urine samples during the collection period.
Interpretation
The findings suggest that plasma is a more reliable matrix for detecting retatrutide compared to urine, aligning with the pharmacokinetic profiles of long-acting peptides. While the statistical significance of the detection limits is established, the clinical relevance may be limited due to the small sample size. The lack of detection in urine raises questions about the applicability of urine testing for this compound in antidoping contexts.
Key findings
- LOD of 6.14 ng/mL in plasma and 2.44 ng/mL in urine.
- Plasma concentration-time profiles exhibited nonmonotonic behavior.
- Extended plasma detection window of approximately 56 days after the first dose.
Limitations
- small n=4 participants
- no intact retatrutide detected in urine samples
- short follow-up period for pharmacokinetics