📊 PK Steady-State Visualizer
Plot plasma concentration across repeat doses. See exactly when a peptide reaches steady state, how much it fluctuates between doses, and how dose timing shapes the curve.
Why This Chart Matters
Single-dose decay (how fast one injection clears) is only half the picture. With repeat dosing, each new dose stacks on top of what remains from previous doses — until you reach steady state, where input and clearance balance out. The shape of that curve tells you how aggressive your protocol is, whether you’ll see large peak-to-trough swings, and how long it takes before the compound stabilises in your system.
Short half-lives need frequent dosing to stay near steady state. Long half-lives build up slowly — semaglutide takes 4–5 weeks to plateau. Picking the wrong interval produces either rollercoaster plasma levels or wasted dose.
- Blue line: plasma concentration over time
- Dashed teal line: steady state average
- Dashed orange band: steady state peak & trough
- Tick marks on x-axis: each dose event
- Right-side readout: accumulation ratio, time to steady state, peak-to-trough fluctuation
Protocol
Steady State PK — FAQ
What is steady state in pharmacokinetics?
Steady state is the point at which the amount of drug entering your body each dosing interval equals the amount being cleared. Before steady state, the compound accumulates with each dose. At steady state, plasma concentration oscillates between a predictable peak (right after each dose) and trough (right before the next dose). As a rule of thumb, it takes 4–5 half-lives to reach ~95% of steady state.
Why does semaglutide take so long to reach steady state?
Semaglutide has a terminal half-life of approximately 165 hours (~7 days). Four to five half-lives is 4–5 weeks. This is why GLP-1 titration schedules escalate dose slowly over 16–20 weeks — raising the dose before the previous level has stabilised produces exaggerated side effects. Short half-life peptides like BPC-157 (~4 h) reach steady state within a day.
What is a healthy peak-to-trough ratio?
Lower is generally better — it means your plasma levels stay more consistent between doses. A ratio of 1.5× or less is considered flat and well-tolerated. 2–3× is typical. Above 4× you get large plasma swings that can produce side effects right after dosing and loss of effect before the next dose. If your ratio is high, decreasing the dose and increasing the frequency usually smooths the curve.
What is the accumulation ratio?
The accumulation ratio is how much higher the steady state average concentration is compared to the average after a single dose. For weekly dosing of a long-half-life compound like semaglutide, the accumulation ratio is around 2–3× — meaning your plasma levels at steady state are 2–3× higher than they would be after your very first injection. This is why first-dose side effects underestimate what you’ll feel at steady state.
Does this chart account for absorption time?
No — this is a simplified single-compartment first-order elimination model. It assumes instant absorption after each dose. Real subcutaneous injections have a short absorption phase (minutes to hours) that smooths the peak slightly. For most practical dosing decisions the simplification does not change the picture meaningfully, but for very short-half-life peptides the real curve will be somewhat flatter than shown.
Why do you use “relative units” instead of mg/L?
Converting to actual mg/L concentration requires the volume of distribution (Vd), which is poorly characterised for many research peptides. Relative units let you compare dosing schedules and see the shape of the curve — which is what matters for protocol decisions — without claiming more precision than the pharmacology supports. If you want approximate mg/L, dose in mg and divide the chart values by your estimated Vd in litres.