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## What is Pharmacokinetics?

You might think this is a simple question, especially for an expert in pharmacokinetics. Well, this question is full of controversy with each scientist having their own opinion. I think this is because the definition of pharmacokinetics is simple, yet pharmacokinetics science is broad in scope.

The word pharmacokinetics is from two greek words (see wikipedia for more):

pharmakon: drug
kineticos: to do with motion

Simply put, pharmacokinetics is a study of the movement of drug in the body.

### Drugs are are like apple pie

Think about eating a slice of apple pie. After you put the scrumptious food in your mouth, it travels to your stomach and eventually to your intestines. Then your body begins to absorb the nutrients in the pie. Following the absorption process, the body distributes the nutrients to different tissues (eg muscles, brain, lungs, etc.). Once at the tissue, the body converts the nutrients into energy, adipose tissue, etc. Finally, any leftover chemicals are eliminated from the body in the urine or the feces.

A drug is no different from a slice of apple pie. After you swallow a drug, it moves to your stomach where the body begins to absorb the drug. The body then distributes the drug to different tissues in the body. Once at the tissues, the body recognizes that the drug doesn’t belong in the body and it begins to convert the drug into something that will be eliminated from the body (ie metabolites). These metabolites are then transported to the kidneys to be eliminated in the urine or the liver to be eliminated in the feces.

### Pharmacokinetics and math

The science of pharmacokinetics utilizes mathematical equations to describe the movement of the drug from the pill through the body, and finally into the urine and feces. These mathematical equations are similar to Einstein’s nature of energy E=mc2 or Pythagorean’s theorem a2+b2=c2. The equation used in pharmacokinetics is C(t)=C0e-kt, where C is the drug concentration, k is the rate of elimination, and t is the time since swallowing the pill.

It’s easy as apple pie! All you have to remember is that pharmacokinetics is the study of the movement of drug in the body.

The methods used to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of a compound can be inherently complex and sophisticated. PK/PD analysis is a science that requires a mathematical and statistical background, combined with an understanding of biology, pharmacology, and physiology. PK/PD analysis guides critical decisions in drug development, such as optimizing the dose, frequency and duration of exposure, so getting these decisions right is paramount. Selecting the tools for making such decisions is equally important. Fortunately, PK/PD analysis software has evolved greatly in recent years, allowing users to focus on analysis, as opposed to algorithms and programming languages. Read our white paper to learn about the key considerations when selecting software for PK/PD analysis.