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Pharmacokinetics is one of the more commonly used, and one of the more important, terms that you will see in journals and online. Learn more about it here.
When you are researching substance uses, you may come across some sophisticated terminology. Most scientific terms are used on websites or in articles that are not common knowledge. One of the terms that you should be familiar with is pharmacokinetics. It is one of the more commonly used, and one of the more important, terms that you will see in journals and online.
Pharmacokinetics is a specific branch of pharmacology. It is focused on the study of the movement of drugs throughout the body. The term “body” in this definition refers specifically to the living organism that the drug is being administered to. It can mean human or animal bodies, but ultimately the study is concerned with the way drugs travel in and affect the human body.1
Several factors can affect the way that drugs are distributed throughout the body. They’re largely related to variables that are specific to patients. Some of the most commonly referred to factors that affect pharmacokinetics are:
There are many different metrics used when discussing pharmacokinetics. Some of them are familiar, while others are a bit more scientific in nature. A few examples of common metrics are listed below:
The knowledge of how a drug behaves informs the suitability of a drug for its target. If this information is not gathered, the drug being used may cause death or adverse effects. Pharmacokinetics provides accurate data for preclinical trials, which then inform clinical trials. It allows the professionals studying the drug to create suitable initial doses, and any possible side-effects can be managed accordingly.
When preparing for clinical trials, the most important pharmacokinetic principles are distribution, absorption, metabolism, and excretion. All of these areas of study inform the way that the drug is given and distributed, and how it can be expected to process and exit the body.
Pharmacokinetics studies the way that drugs move throughout the body. As such, pharmacokinetics can be applied to factors that change the effects that drugs have on the brain. Understanding how the drug is going to be absorbed in the body is important.1
If the body absorbs the drug before it reaches the brain, it will be less effective. Pharmacokinetics can inform how the drug should be absorbed (water-solubility vs. fat-solubility), thus affecting the brain.
When looking into pharmacokinetics, you are likely to come across the acronym LADME. The acronym breaks down to the following terms:2
Drugs are absorbed into the body’s bloodstream. When they are in the bloodstream, they circulate throughout the body and are absorbed by the body’s tissues. Once they are absorbed, they do not spread evenly throughout the rest of the body. They target specific parts of the body.
There are a number of ways that drugs are absorbed in the body. Most are absorbed through passive diffusion, however, meaning that they are taken orally, and make their way to the gastrointestinal system. At that point, they are dissolved and passed into the bloodstream.
Drugs are metabolized in a number of ways in the body. They can be metabolized through oxidation, reduction, hydrolysis, hydration, conjugation, condensation, or isomerization. These processes break the drug down into a more manageable compound, making it easier to excrete from the body. Most of the enzymes that metabolize the drugs are located in the tissues of the body and are heavily concentrated in the liver.
Drugs are excreted from the body in several different ways. The method of excretion is dependent upon how the drug is metabolized. Water-soluble drugs are eliminated by the kidneys and are excreted via urine. Others are fat-soluble and are excreted via bile created by the liver. Other forms of excretion occur through sweat, saliva, and milk (in women who are lactating).
Two models are used to determine a drug’s pharmacokinetics. They differ from one another and are used in different trials to inform different aspects of each drug.
This form of analysis is model-independent, meaning that it does not rely on assumptions about body compartments. Noncompartmental methods are known for providing more consistency throughout testing. They are also less complex than compartmental methods and require less mathematical rigor. Because of this aspect, they are often faster and more cost-effective than compartmental models.3
Compartmental methods take into consideration all different systems in the body. They are referred to as compartments. The compartmental method lends itself to the belief that all of the systems are interconnected. As such, the regression from system to system is taken into consideration.
This model requires more math, as well as more testing. These methods are highly complex and take a large amount of money to accomplish. Each test or method may take into account different variables, as each pharmacokinetic professional will have different assumptions.3
The relationship between the single-dose concentration of a drug and time is called the drug concentration-effect relationship. It describes the way that drug concentration in the body falls exponentially with time. The highest concentration is in the body just after the absorption of the drug. Then, the concentration falls exponentially for a specific period afterward. However, after the half-life has been reached, the excretion of the drug slows exponentially as well. This fact is, again, due to the half-life of the drug itself. See the example below.4
There is a superstition that taking repeated doses creates a larger buildup of the drug in the body, therefore taking longer to excrete. However, this belief is untrue. The drug still has the same half-life, meaning that it leaves the body at the same rate.
As such, adding a repeated dose does not increase concentration in the way that you would think. It can increase the time that it takes the drug to leave the body from the first dose, but the amount of time to be excreted from the repeated dose to no substance being left in the body is the same.
When you are researching pharmacokinetics, you’ll likely come across the term pharmacodynamics. The two terms are very different, but they are related.
Pharmacokinetics, as described before, is the study of the movement of drugs in the body. It focuses on the drug when it comes to the area being studied. It characterizes absorption, distribution, bioavailability, metabolism, and excretion in terms of time.5
Pharmacodynamics, on the other hand, is the study of the body’s biological response to drugs. It focuses on the biochemical and molecular responses triggered by the substance being introduced to the body.5
The two can be compared through the exposure-response relationship. It characterizes drug exposure, predicts dosage requirements, estimates rates of absorption and elimination. By analyzing pharmacokinetics and pharmacodynamics side by side, most information regarding the way a drug will affect a person can be predicted, which results in the information provided on most approved drug labels, as well.
Overall, you should care about pharmacokinetics because they help to determine any key factors associated with drugs. Through testing and analysis, pharmacokinetics inform standard doses, dosing intervals, bioavailability, concentration, and excretion.
When used in conjunction with pharmacodynamics, all information about how the drug will affect the body, as well as how the body will react to the drug, can be determined. It is the standard for approving any medications in the pharmaceuticals industry.
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