How peptide dosing patterns shape exposure
See how a subcutaneous dose and repeated administration translate into model-estimated semaglutide concentration in blood plasma—and explore why concentration is not the same as biological effect.
Predicted plasma concentration is not the same as biological effect or safety. A curve that appears to have “room” does not demonstrate a safety margin. The model does not recommend a peptide, dose, schedule, or treatment and does not replace medical advice. See the full limitations.
1. Plasma concentration after repeated dosing
Choose a subcutaneous dose and schedule to see the plasma concentration predicted by a published population pharmacokinetic model for semaglutide. Each administration adds to what has not yet cleared. This is an estimate for the publication's reference profile—not a measurement or prediction for an individual.
What is being estimated? Semaglutide concentration in blood plasma after subcutaneous administration—not concentration at the injection site, in an organ, or at a receptor.
Published basis: one compartment, first-order absorption and elimination; ka = 0.0286 h⁻¹, CL/F = 0.0478 L/h, and V/F = 12.2 L. The reference profile was an 85 kg woman under 65 with type 2 diabetes and normal renal function, using abdominal injection. Population PK publication.
The shaded band is a clearance-sensitivity illustration derived from the publication's reported 12.9% post-covariate between-subject variability. It excludes residual error and uncertainty in absorption and distribution, so it is not a patient prediction or a complete population interval.
Retatrutide investigational: the phase 1b publication reports a median time to peak of 12–48 hours across groups and a half-life of approximately 6 days. Those values can shape a dose-normalized curve, but the published parameters used here are insufficient to convert 1 mg into a defensible absolute plasma concentration. Phase 1b publication.
The uncertainty controls in this mode are user-selected scenario ranges, not study confidence intervals.
What to explore
Change the dose, interval, and number of administrations. The curve reports model-estimated plasma concentration in both nmol/L and ng/mL. Dose changes scale concentration under the publication's linear-PK assumption; the model does not translate concentration into benefit, adverse effects, or a recommended regimen.
2. Equal dose changes may not be equal biological changes
A saturating Hill relationship can be written as response = D^h/(D^h + EC50^h). Under this illustrative assumption, the same absolute change in relative dose can produce very different changes in modeled response at different parts of the curve. This is a mathematical demonstration, not a titration or treatment schedule.
| step | linear relative dose | modeled response % | change | equal-response dose | modeled response % | change |
|---|
The left-hand path subtracts the same amount of relative dose at every step, producing increasingly unequal modeled response changes. The right-hand path keeps the modeled response change constant, which requires progressively smaller relative-dose steps. These values are dimensionless illustrations and must not be read as milligrams or a clinical schedule.
EC50 and the Hill coefficient must come from appropriate evidence for the specific compound, endpoint, and context. Guessed values produce precise-looking but unsupported results.
What this model does not tell you
- Concentration is not effect. The first section is pharmacokinetic, not pharmacodynamic. It does not model efficacy, adverse effects, or the factors that limit a real dose.
- Apparent “room” on a curve is not a safety margin. Dose-limiting harms are not represented as simple concentration thresholds.
- Absolute output is still a population-model estimate. The semaglutide mode uses published apparent clearance and distribution parameters for a defined reference profile; it is not a blood test or an individualized forecast. The advanced hypothetical mode remains dose-normalized.
- One-compartment linear kinetics are an approximation. Real peptide behavior may involve complex absorption, multiple compartments, nonlinear clearance, route-specific variation, and time-varying immunogenicity.
- Inter-person variability may be substantial. This tool does not estimate an individual's clearance or response.
- Tolerance, desensitization, and downstream adaptation are excluded. The model can therefore miss mechanisms that materially change response over time.
- The Hill response is a surrogate. It is useful for illustrating nonlinearity but does not establish clinical benefit, risk, or the correct biological endpoint.
- Some kinetics lie entirely outside the model. Saturable, target-mediated, or otherwise nonlinear disposition may not follow these equations.
- Patient-specific contraindications and interactions are invisible. Medical history, other treatments, product quality, and monitoring requirements are outside the model.
The model is inspectable: a one-compartment Bateman-function superposition with a separate Hill/Emax teaching layer. Semaglutide mass concentration is converted to molar concentration using a molecular weight of 4113.58 g/mol from the current FDA prescribing information. The displayed bands are model-sensitivity illustrations, not confidence intervals.