Peptide Half-Life Visualizer

Select a peptide to simulate how plasma concentration changes over time using exponential decay pharmacokinetics. Visualize single and multi-dose protocols with key metrics including peak concentration, trough levels, and clearance timelines.

Understanding half-life helps determine optimal dosing frequency — too infrequent leads to subtherapeutic troughs; too frequent causes unnecessary accumulation.

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How Peptide Half-Life Works

Peptide half-life follows first-order kinetics: at each half-life interval, exactly 50% of the remaining compound is eliminated. A 250 mcg dose of a peptide with a 4-hour half-life will drop to 125 mcg at 4h, 62.5 mcg at 8h, and approximately 8 mcg by 24h.

The formula used here is the standard single-compartment exponential decay equation: C(t) = C0 x (0.5)^(t / t1/2). For multi-dose protocols, concentrations from each dose are summed at each time point (superposition principle), which holds for linear pharmacokinetics.

Limitations of This Model

Half-life values are approximations from published research and may differ significantly between individuals based on weight, age, metabolic rate, and renal/hepatic function.
This tool uses a simplified single-compartment pharmacokinetic model. Real peptide distribution often involves multiple compartments.
The model does not account for receptor saturation, tolerance, or down-regulation with repeated dosing.
Subcutaneous absorption delay is not modeled — actual Tmax may occur later than shown.

Sources and References

Pharmacokinetics and Pharmacodynamics of Peptide Drugs. Journal of Pharmaceutical Sciences.
CJC-1295 Drug Affinity Complex: Extended Half-Life of a GHRH Analogue. Journal of Clinical Endocrinology & Metabolism.
BPC-157: A Review of Its Gastroprotective and Systemic Healing Properties. Current Pharmaceutical Design.

Frequently Asked Questions

What is peptide half-life and why does it matter for dosing?

Half-life (t½) is the time required for the plasma concentration of a peptide to decrease by 50%. It determines how frequently a peptide must be administered to maintain therapeutic levels and how long it remains active after injection. A peptide with a 2-hour half-life requires much more frequent dosing than one with an 8-day half-life like CJC-1295 with DAC.

Why do peptides have such short half-lives compared to small-molecule drugs?

Peptides are chains of amino acids recognized and cleaved by proteolytic enzymes (peptidases and proteases) throughout the body. This enzymatic degradation happens rapidly. Some modifications, like the DAC (Drug Affinity Complex) in CJC-1295 with DAC, extend half-life by binding the peptide to albumin in the blood.

What is the difference between subcutaneous and IV administration half-life?

Intravenous (IV) delivery places a peptide directly into circulation, so the half-life reflects purely how fast the body clears it. Subcutaneous (SC) injection deposits the peptide under the skin, where absorption into capillaries is slower. This creates a delayed, sustained blood-level profile that can extend the effective duration beyond what the elimination half-life alone suggests.

What does "steady state" mean in multi-dose peptide protocols?

Steady state is reached when the rate of drug input (dosing) equals the rate of elimination. After approximately 4–5 half-lives of repeated dosing, the trough (lowest) and peak (highest) concentrations stabilize. For peptides with very short half-lives, steady state is reached quickly. For CJC-1295 with DAC (t½ ~8 days), it takes 32–40 days of weekly injections.

Why is the half-life of Selank and Semax only a few minutes?

Selank and Semax are short neuropeptides designed for nasal administration. Their plasma half-lives are extremely short (2–3 minutes), but CNS activity can persist longer due to receptor binding and downstream signaling effects. This is why route of administration and biological effect duration are often discussed separately from plasma half-life for these peptides.

Does the concentration chart account for first-pass metabolism?

No. This model simulates systemic plasma concentration using a simplified single-compartment first-order decay model. First-pass metabolism is not applicable to injectable peptides. The model also does not account for tissue binding, multi-compartment distribution, non-linear kinetics, or individual variation in clearance.