Influence of sample handling conditions on drug partitioning in blood: a major problem in PK studies?

“...most guidelines on bioavailability, for example, those of the US FDA, do not clearly consider that in the bloodstream there are at least two compartments, plasma and blood cells, giving more precise indications on sampling and bioanalytical approach.” Systemic circulation is the most accessible body compartment. Since it is a crossroad between drug absorption, distribution, metabolization and excretion for molecules with systemic action and several locally acting drugs, it is preferred in most PK studies. However, most guidelines on bioavailability, for example, those of the US FDA [1], do not clearly consider that in the bloodstream there are at least...