Pharmacokinetics and pharmacodynamics are two divisions within pharmacology sciences that evaluate drug and human body interaction. Clinical pharmacology is a branch that studies the interaction between drugs and the human body. Pharmacodynamics (PD) and pharmacokinetics (PK) assess how the body’s natural processes interact in the presence of a drug product. Such evaluations are crucial for determining the safety and efficacy of a pharmaceutical drug product.
The US FDA is accountable for bringing safe and effective drug products to the US market. Hence, they are also responsible for the satisfactory conduct of the drug development process. Having said that, what is the process of drug development? The ultimate goal of the drug development process is to identify potential compounds and turn them into safe and effective drugs against disease and medical conditions. Developing safe and effective drug products partly depends on pharmacokinetic and pharmacodynamic studies. However, both these studies have critical differences. Let us understand the differences between pharmacokinetics and pharmacodynamics.
Pharmacokinetics (PK) vs. pharmacodynamics (PD)
PK sample analysis involves studying how a drug is absorbed, distributed, metabolized, and excreted from the body. The primary difference between PK and PD is that PK studies the drug movement through the body while PD evaluates the effect a drug has on the human body. To put it simply, PK is what the human body does to the drug product, while PD is what the drug product does to the human body. On the other hand, PD assesses the body’s response or the impact the drug product has on the body.
While pharmacokinetics study design predominantly depends on the ADME properties and bioavailability, pharmacodynamics is the evaluation of molecular and biochemical interactions. Thus, PK/PD can be coupled as an exposure/response interrelation.
Though PK and PD are two distinct parameters, understanding them together is crucial for the successful approval of a drug product. About 25% of drug label data comes from PK/PD studies. Hence, a strategic approach to drug development with an efficient pharmacokinetic study design is crucial to accelerate the entire process of drug development. Let us now focus on how PK drug data and PD analysis are vital for drug discovery and development.
Importance of PK/PD studies
PK/PD data provides vital information on how the body interacts with the drug product. Drug developers use PK/PD data to design better clinical trials, while clinicians use PK/PD data to treat different patient populations. PK/PD data has numerous applications in drug discovery and development. Some primary applications are highlighted below.
- Characterize drug exposure: Other than intravenous drugs, most drugs are not completely absorbed in the body. Hence, understanding plasma PK properties and drug exposure are crucial to determining the best dosage for clinical use.
- Determine appropriate dosage: PK studies are preliminary studies to assess the safety and efficacy of a drug product. SAD and MAD studies are first-in-human studies that help determine safe dosage for subsequent human trials.
- Estimate absorption and elimination rates: Understanding the rate at which a drug compound is absorbed and eliminated from the body is necessary to design drug formulation and dosing regimens.
- Bioavailability/bioequivalence assessments: PK/PD studies provide crucial data regarding the ADME properties of new drugs compared to their reference-listed drug product.
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