Pharmacokinetics (PK)

What is pharmacokinetics (PK)?

Pharmacokinetics is the study of how the body affects a drug. It describes the drug’s absorption, distribution, metabolism, and excretion.

  • Absorption: How the drug moves from the site of administration to the site of action
  • Distribution: The journey of the drug through the bloodstream to various tissues and organs
  • Metabolism: How the body breaks down the drug into smaller molecules
  • Excretion: The removal of the drug from the body

Pharmacokinetics is different from pharmacodynamics, which explores how drugs affect the body. However, both are necessary to understand the effect of a drug on the body.

The pharmacokinetics of a drug depends on the drug’s chemical properties in addition to patient-related factors. In some cases, the patient-related factors (e.g., sex, genetic makeup, age, renal function) can be used to predict the pharmacokinetic parameters in a specific population.

Why is pharmacokinetics important for healthcare?

Pharmacokinetics determines the onset, degree, and duration of the drug’s effects. Knowing these qualities is crucial for demonstrating the safety and efficacy of a drug, which is needed to obtain FDA approval.

Additionally, understanding pharmacokinetic principles allows prescribers to adjust dosages more accurately. This means that prescribers can modify the dosage based on the patient’s lifestyle and physiology, creating the greatest benefit at the lowest risk. This is aided by the dose-exposure response—used to determine the optimal dose needed to achieve the desired drug exposure and physiologic response—which relies on both pharmacokinetics and pharmacodynamics.