Pharmacology is the study of drug interactions with the human body. Under the umbrella of clinical pharmacology, there are many different fields of study, but the most notable two are pharmacokinetics (PK) and pharmacodynamics (PD). 

Both study types focus on the complex chemical interactions between the human body and pharmaceuticals. Both pharmacokinetics and pharmacodynamics examine these interactions (of drugs and natural bodily processes) and use the information gathered to help determine the safety and effectiveness of pharmaceuticals.

Regulatory agencies and health authorities such as the FDA are tasked with drug approval processes for new drugs. They are also responsible for deciding whether a drug should remain on the market. 

Regulatory agencies rely on research and information provided by pharmacokinetic and pharmacodynamic studies to make these important decisions. In addition to approving new pharmaceuticals and deciding if existing drugs should remain on the market, regulatory agencies are also tasked with ensuring that these drugs perform how they should and are safe for human consumption. 

Thanks to pharmacokinetics and pharmacodynamics, this FDA approval process exists. Without these research fields, the safety and efficacy of pharmaceuticals would be much more challenging to understand. 

• Pharmacokinetics (PK) Study: Drug Concentration vs. Time in the Body – A pharmacokinetic (PK) study provides the basis for determining how drugs work within the human body, often over specific time periods. The main factors that are researched within a pharmacokinetic analysis make up the acronym ADME (absorption, distribution, metabolism, and excretion).

• Absorption – Absorption is typically the first thing looked at in pharmacokinetic studies. Absorption is described as the process that happens when a pharmaceutical begins to be circulated within the bloodstream. In clinical PK studies, drugs are often administered in various ways (oral, dermal, nasal, etc.). After administration, the body’s reaction to the drug and the drug’s effectiveness is recorded.

• Distribution – Distribution is the term used for the disbursement of an unmetabolized pharmaceutical within the body’s blood and tissues. Drug distribution inside the body can create favorable and adverse events or outcomes due to many different factors. These factors include lipid solubility, plasma concentration, tissue concentration, protein binding, and more. With the help of PK studies, a better understanding of how certain drugs circulate through the body can be achieved. 

• Metabolism – Metabolism, one of the more closely studied categories within PK research, is the process in which a pharmaceutical is converted into a different chemical within the body. The metabolizing process happens mainly within the liver organ. Various factors can influence the rate at which a drug metabolizes, including general health, drug administration type, drug dosage, genetics, metabolic activity, and more.
• Excretion – The expelling of bodily waste, known as excretion, is commonly the last stage of a PK study. Researchers look at how the body expels pharmaceuticals and other substances and also how long it takes for the body to do so. Most pharmaceuticals within the body are expelled through the urination process. An essential factor for the excretion process (as it relates to a PK study) is a drug’s solubility in water. The more soluble a drug is, the more quickly they are excreted through urination.