What are the major issues involved in defining the pharmacokinetic properties of a drug?

Pharmacokinetic properties of a drug refer to its absorption, metabolism, distribution and elimination from the body. The major issues involved in defining the pharmacokinetic properties of a drug arise because the exact way the drug interacts with the body depends on a number of factors including but not limited to age, gender, genetics, body weight, body composition, diet, pregnancy status, and pathophysiology. These variations in individuals impact the way their body reacts to a drug. This makes it challenging to define the pharmacokinetic properties of any drug.