sentences:  For example, when an individual is exposed to a drug or toxin, the concentration of that drug or toxin within the body, or the biological effective dose, provides a more accurate prediction for the effect of the drug or toxin compared to an estimation or measurement of the toxin from the origin or external environment.Pharmacodynamic (PD) biomarkers can measure the direct interaction between a drug and its receptor.Pharmacodynamic biomarkers reveal drug mechanisms, if the drug has its intended effect on the biology of the disease, ideal biological dosing concentrations, and physiologic response/resistance mechanisms.