Pharmacokinetics: Kinetics  = Has to do with movement. How the body moves and metabolizes the drug and eventually excretes it.  Dictionary.com says Pharmacokinetics is “the study of the movement of drugs in the body, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion“. A second definition says, Pharmacokinetics refers to “Movements of drugs within biologic systems, as affected by uptake, distribution, binding, elimination, and biotransformation; particularly the rates of such movements.”

Pharmacodynamics: Dynamos means power. It’s how the drug works. How it exerts its power on the body. Pharmacodynamics = Relating to drug action, particularly at the receptor level.

“Pharmacodynamics is the study of how a drug affects an organism, whereas pharmacokinetics is the study of how the organism affects the drug.”

“The term pharmacokinetics (PK) refers to the study of
-How fast and how completely the drug is absorbed into the body (from the stomach and intestines if it’s an oral drug)
-How the drug becomes distributed through the various body tissues and fluids, called body compartments (blood, muscle, fatty tissue, cerebrospinal fluid, and so on)
-To what extent (if any) the drug is metabolized (chemically modified) by enzymes produced in the liver and other organs
-How rapidly the drug is eliminated from the body (usually via urine, feces, and other routes)

The term pharmacodynamics (PD) refers to the study of
The relationship between the concentration of the drug in the body and the biological and physiological effects of the drug on the body or on other organisms (bacteria, parasites, and so forth) on or in the body.

Generations of students have remembered the distinction between PK and PD by the following simple description:
Pharmacokinetics is the study of what the body does to the drug.
Pharmacodynamics is the study of what the drug does to the body.” From Dummies.com

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