There are several potential reasons for multiple peak plasma concentrations.
One of which is gut-liver (enterohepatic) recycling (EHR) of drugs.
- A drug is systemically absorbed, yielding the first peak plasma concentration (Cmax1)
- The drug is processed to form a metabolite (conjugate) in the liver.
- The metabolite is excreted via bile (a bitter fluid) back to the intestine.
- The metabolite is broken down (deconjugated) to the parent drug by gut bacteria.
- The recovered parent drug is reabsorbed from intestine to blood, yielding a second peak plasma concentration (Cmax2).
Why is this EHR important for our health?
It explains why our gut health (i.e. gut bacteria) can affect drug handling in our body and its treatment (therapeutic) effect.