Clinical pharmacology is the science of drug interaction with the human body. Pharmacokinetics (PK) and pharmacodynamics (PD) are two broad segments falling under clinical pharmacology. PK studies numerous biochemical interactions occurring between the body and the pharmaceutical drug. Moreover, PK and PD also measure the chemical composition and drug interaction in the human body, making them crucial for determining drug efficacy and safety.
Toxicology studies in drug development are primarily dependent on PK/PD data. Regulatory agencies rely on toxicology studies to assess the efficacy and safety of drug products for human use. Comprehending the effectiveness and safety of drug products, largely, depends on both PK/PD studies and tox studies. However, there are some primary differences between PK/PD studies. The current article highlights the three key differences between PK and PD data.
PK vs. PD
The primary difference between PK and PD is that PK studies the effect a body has on the drug product. On the other hand, PD helps understand the influence a drug has on the body.
Kinetics means motion. Although, by definition, kinetics studies the effect of forces on mechanisms. Hence, PK assesses the movement of a drug product through the body. Dynamics is usually related to power or change. Thus, PD refers to the effect of a pharmaceutical drug and how it changes the human body.
PK evaluates the rate of chemical interactions. It assesses chemical reactions based on the ADME properties, i.e., absorption, distribution, metabolism, and excretion properties of a drug product. IN contrast, PD evaluates drug interactions based on biochemical associations. PD focuses on chemical interactions, receptor-binding, and post-binding effects.
Importance of PK/PD data
Understanding early PK/PD relationships is crucial for the success of drug development programs. About 25% of drug label data comes from PK/PD analysis. Hence, strategic planning of PK/PD studies can help accelerate drug development timelines and help ensure safe and effective drug products. Drug developers use the understanding gained from PK/PD studies to navigate clinical trials. PK/PD data help them design drug doses depending on different drug interactions within the human body. Besides, PK/PD information on drug labels helps clinicians decide drug doses for distinct patient populations. For example, younger vs. older patients or patients with or without liver impairment.
Applications of PK/PD data in drug development programs
PK/PD data has numerous applications in drug discovery and development. Following are some benefits of PK/PD data in clinical studies.
- Except for intravenous drugs, only a fraction of drug compounds are absorbed in the body. Hence, PK/PD data help characterize the drug exposure profile and quantify the rate of drug exposure.
- As mentioned above, PK/PD data helps determine the drug doses in early development studies and eventually makes the initial dose-range finding studies robust and informative.
- PK/PD studies help identify clear therapeutic windows and thus establish efficacy characteristics and safety margins.
- Importantly, PK/PD studies help assess the rate of drug absorption and elimination. This data helps drug developers make informed decisions regarding drug formulation and doses.