What is pharmacokinetics (AUC, Cmax)?
Pharmacokinetics describes what the body does to a substance: how it is absorbed, distributed, broken down and excreted. It is measured through the blood concentration over time. Figures such as AUC, Cmax and half-life show how much of a compound arrives and how long it stays.
Pharmacokinetics explained simply
Pharmacokinetics (PK) answers four questions, often summed up as ADME:
- Absorption: how much passes from the gut into the blood? (see absorption)
- Distribution: where does the compound travel in the body?
- Metabolism: how is it converted, above all in the liver?
- Excretion: how does it leave the body, for example via the kidneys or bile?
It is distinct from pharmacodynamics, which describes what a compound does in the body. PK therefore says nothing about whether a compound works, only whether and how much of it reaches its target.
The key figures
How to read PK studies: these values come from the blood concentration over time.
| Figure | Meaning | What it shows |
|---|---|---|
| Figure Cmax | Meaning highest measured concentration in the blood | What it shows the maximum that arrives |
| Figure Tmax | Meaning time to the peak value | What it shows how quickly absorption occurs |
| Figure AUC (area under the curve) | Meaning area under the concentration-time curve | What it shows the total amount absorbed over time |
| Figure Half-life | Meaning time for the concentration to fall by half | What it shows how quickly the compound is broken down |
Pharmacokinetics of curcumin
For curcumin, the PK data are the heart of the problem: free curcumin is poorly absorbed, quickly broken down in liver and gut (first-pass effect) and in animal and cell experiments has a short half-life of only a few minutes. In the blood one therefore mostly finds breakdown products (glucuronides) and little free curcumin.
When manufacturers talk about "x-fold bioavailability", the numbers almost always come from PK studies in healthy participants, usually comparing AUC. When reading, ask: which measure was compared (total curcuminoids or free curcumin)? Against which reference product? How many people took part? One example is a small pilot study of a γ-cyclodextrin formulation (European Journal of Nutrition, 12 healthy adults, double-blind, crossover): about 39 times the AUC of total curcuminoids and 85 times for curcumin (dose-normalised) compared with an unformulated standard extract. That is a statement about absorption in healthy people, not evidence of an effect on any complaint.
PK studies are usually small (often 10 to 30 people) and done in healthy volunteers. They say something about absorption, not about the benefit of a product. Statements about effects need their own clinical studies.
Frequently asked questions about pharmacokinetics
What is the difference between pharmacokinetics and pharmacodynamics? Pharmacokinetics: what the body does to the compound. Pharmacodynamics: what the compound does in the body.
Why are PK studies often so small? They require many blood samples per person, are laborious and manage with few participants, especially in a crossover design in which each person receives both products in sequence.
Can I conclude a better effect from a higher AUC? No, only that more of the compound was absorbed. Effects need clinical studies.
