Pharmacokinetics and pharmacodynamics are distinct concepts. Pharmacokinetics is the study of the pathway the drug makes in the body from ingestion until it is excreted and pharmacodynamics is the study of the interaction of this drug with the binding site that will occur during this pathway.
Pharmacokinetics
Pharmacokinetics consists of studying the path the drug will take from the time it is administered until it is eliminated, through absorption, distribution, metabolism and excretion processes. In this way, the drug will find a binding site.
1. Absorption
Absorption is the passage from the drug where it is given to the bloodstream. Administration may be done enterally, which means that the remedy is ingested via the oral, sublingual or rectal route, or parenterally, which means that the drug is administered intravenously, subcutaneously, intradermally or intramuscularly.
2. Distribution
The distribution is the path the drug makes after it crosses the barrier of the intestinal epithelium into the bloodstream and may be in free form or bound to plasma proteins and may then reach several sites:
- Place of therapeutic action, where it will exert the intended effect;
- Tissue reservoirs, where it will be accumulated without exerting therapeutic effect;
- Unexpected place of action, where you will carry out an unwanted action causing side effects;
- Place where they are metabolized, being able to increase their action or to be inactivated;
- Locations where they are excreted.
When a drug binds to plasma proteins it can not cross the barrier to reach the tissue and exert therapeutic action, so a drug that has high affinity for these proteins will have a lower distribution and metabolism. Ente moreenteente moreente moreente moreente moreente moreenteenteente moreente moreente more more more moreentees moreente moreenteenteente moreente moreenteenteenteenteentees moreente use moreente moreenteenteenteenteenteenteente morees more more more morees more more moreente morees more moreentees more more morees more morees morees more morees more usees more more use moreenteenteesenteente moreenteente moreenteente use
3. Metabolism
Metabolism occurs largely in the liver, and the following may occur:
- Inactivate a substance, which is the most common;
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- Activate originally inactive compounds, changing their pharmacokinetic profile and forming active metabolites.
Drug metabolism may also occur less frequently in the lungs, kidneys, and adrenal glands.
4. Excretion
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Pharmacodynamics
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1. Place of action
The sites of action are the places where endogenous substances, which are substances produced by the body, or exogenous, which is the case of medicines, interact to produce a pharmacological response. The main targets for the action of the active substances are the receptors where they usually bind endogenous substances, ion channels, transporters, enzymes and structural proteins.
2. Mechanism of action
The mechanism of action is the chemical interaction that a particular active substance exerts with the receptor producing a therapeutic response.
3. Therapeutic effect
The therapeutic effect is the beneficial and desired effect that the drug causes in the body when administered.
