Differences Between Pharmacokinetics and Pharmacodynamics

11 April, 2021
While pharmacokinetics studies the changes that the body produces in the drug and the active ingredient; pharmacodynamics evaluates the effect of the drug in the body. Learn more about the difference between pharmacokinetics and pharmacodynamics.

When it comes to understanding a drug’s package leaflet, as well as its properties and the effects it triggers in the body, it’s essential to understand the differences between pharmacokinetics and pharmacodynamics. Both terms are topics within the broader science of pharmacology.

Pharmacology studies different drugs, understanding drugs as chemical substances that, in one way or another, can alter the biochemical and physiological processes of the human body. Medicinal drugs have both therapeutic or preventive purposes.

So, pharmacokinetics is the study of how the body absorbs, distributes, metabolizes, and excretes any drug. On the other hand, pharmacodynamics is the study of the mechanisms and effects that a drug produces once it’s been administered.

Let’s now take a look at the main characteristics of both pharmacokinetics and pharmacodynamics.

Characteristics of pharmacokinetics

As we already know, pharmacokinetics is a part of pharmacology. Specifically, it studies the different processes that a drug goes through after administration. In other words, we can say that it studies the changes that the organism produces in the drug.

The processes on which pharmacokinetics focuses are known under the acronym RADME:

  • Release
  • Absorption
  • Distribution
  • Metabolism
  • Excretion

Release and absorption

Active ingredients are often formulated together with other components that favor certain pharmacokinetic properties. Therefore, for the effect of an active ingredient to take place, it’s necessary for it to be released from its formulation.

After release, the absorption process begins. Through this process, the active ingredient manages to reach the blood, which distributes it throughout the body to reach the different organs.

A woman about to take a pill.
Pharmacokinetics studies the body’s effects on the drug.

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When the active ingredient reaches the bloodstream and the heart pumps the blood, it spreads throughout the circulation. The way the blood distributes the drug can be:

  • Freely.
  • In association with plasma proteins: Many drugs require binding to blood proteins for transportation. Once they’re released from them, they’ll be able to trigger their effect.

In distribution, it’s important to refer to the term bioavailability, which refers to the amount of active ingredient that reaches the blood circulation after administration. Thus, a drug with a bioavailability of 20% will leave 20 milligrams available for every 100 milligrams the patient takes to trigger an effect.

Metabolism and excretion

Metabolism is the set of chemical reactions a drug undergoes in order to make it more soluble in water and facilitate its excretion. Normally, the organ responsible for metabolism is the liver.

Once metabolized, and having undergone the relevant chemical transformations, different excretion routes can eliminate the active ingredient. The main route of drug excretion is the renal route, i.e. through the kidney in the form of urine.

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Characteristics of pharmacodynamics

A pile of pills in front of a variety of pill bottles.
Pharmacodynamics studies how drugs act on the body.

There are many differences between pharmacokinetics and pharmacodynamics. Unlike pharmacokinetics, pharmacodynamics studies the changes that the active ingredient produces in the organism, not the other way around.

Pharmacodynamics studies the result, intensity, and duration of the effect of the active ingredient in the body. It also evaluates the relationship between the drug and its site of action.

For an active ingredient to trigger an action, it’s essential that it should bind to a site of action. Normally, this binding site is where there are proteins called receptors, in the cell walls. Upon activation, they trigger a signaling pathway that results in a biological response.

At the same time, it’s also important to understand the drug’s mechanism of action. This refers to the way in which drugs trigger the effect in the organism when the active ingredient comes into contact with the cell receptors.

Pharmacokinetics and pharmacodynamics: A conclusion

In conclusion, the differences between pharmacokinetics and pharmacodynamics are quite clear if we understand several concepts. If not, we can easily confuse both terms and this will hinder our understanding of many leaflets.

If you have any questions about this, you can ask your doctor or pharmacist to explain the different processes to you. The combination of both is what finally generates the therapeutic or preventive aspect of the drugs.

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