The objective of the Drugs is to be absorbed by the body, regardless of the route of administration. Therefore, these drugs must be able to disintegrate and disintegrate. Now, it is worth asking: how is the absorption of drugs produced?

The answer to this question is: it depends on the physicochemical properties, its formulation and the route of administration.  For example, the tablets are composed of the drug itself, among other ingredients. These can be administered in various ways, which will be discussed in the following.

What is pharmacokinetics?

It is understood as the part of pharmacology that studies evolution. Taking into account the drug concentrations, function of time and dose. Therefore, it addresses from a dynamic point to the quantitative side, since the dose is ingested. Following the following stages:

• Absorption. It is called that way to the process in which a drug passes from outside to an internal environment. 
• Distribution.  After being absorbed, the drugs dissolve in the blood and tissues, passing through biological membranes to join biopolymers.
• Metabolism.  Then there are biochemical changes where the foreign substances become more ionized, polar, water soluble. That is, they are transformed in such a way that they are easier to eliminate than originally.
• Expression To finish the process comes the elimination of drugs that happens mainly in the kidney and liver.

These factors determine the concentration of the drugs in their place of action.

Routes of administration of drugs

On the other hand the routes of administration for the drugs can be direct or indirect.

Direct

In this case, natural barriers such as the skin and mucosa are crossed, producing a rupture thereof. They can be via:

• Subcutaneous
• Intravascular
• Intramuscular

Indirect

They happen when the medication has to go through the natural barrier by itself. Such is the case of:

• Oral.
• Oral.
• Rectal.

What is pharmacodynamics?

It is called this way to the study of the biochemical and physiological effects that the drugs produce in the organism. This process is carried out by means of a receptor, or target, with which the drug joins to initiate its effects and provoke a pharmacological action.

What is a bullseye?

For an effect to exist, the drug has to interact with a target. In molecular biology there are numerous macromolecules that carry out vital functions in the structure of the celland whose alteration is related to some diseases.

These macromolecules are the targets, the place of the organism in which a drug exerts its action. The main biological targets belong to three types of receptor biomolecules:

Lipids

The number of drugs that act on the lipids of the membrane is relatively small. They usually give rise to an alteration of the physical-chemical properties of the same. Such is the case of a large percentage of antiseptics and some antibiotics that act with a mechanism of this type.

These are responsible for three specific tasks in living organisms:

• They act as energy reserves when converted into triglycerides.
• They have a structural function: the phospholipids of the bilayers of the cell membranes.
• They behave like regulatory chemical messengers. That is, steroids.

The biological targets associated with lipids are related to the function of the cell membrane.

Proteins

Proteins form a community of macromolecules in the structure and functioning of the cell. According to their function they are classified in: 

• Enzymes  These are the catalysts of living beings. If there were no chemical reactions in the cells, they would be slow and there would be no life.
• Transport proteins.  They are present in the cell membranes and act as input channels for the molecules that we take with the diet and that are transformed into more complex molecules. Such is the case of the carbohydrates, proteins and nucleic acids found in cells.
• Structural proteins.  It fulfills functions of interaction with other molecules, in such a way that one of these molecules interacts with its target, producing changes or expressions in it.

Nucleic acids

These are the polymer macromolecules that are formed by the union of nucleotides, which in turn form the DNA and RNA molecules.  On the other hand there are some drugs that, during the processes of replication, transcription or translation, have action on Nucleic Acids and cause cell death.

Therefore this group of drugs is used as antineoplastic, antibacterial and antiviral. That is, at the molecular level, most of the drugs that act on nucleic acids give rise to the alteration of their secondary structure.

In the case of DNA, it is translated into the intercalation of the base pairs, followed by alkylation and hydrolysis or by chain cutting.

How do medicines work?

The target cells react with a: hormone, antigen, antibody, antibiotic or other specific substance. These hormones are released into our body through the bloodstream, there they remain until a target cell fits and fulfills its function.

The same hormone can affect different targets and equally a target can be the target of several hormones. Meanwhile, the effects of a hormone on the target are also varied;  that is, more than 50 hormones in the body exert different functions when linked to the proper target.

However, it must be taken into account that the arrival and fixation of the drug in the tissues depends on: 

• The concentration of the drug between blood and tissue.
• Characteristics of the barrier that crosses.
• Degree of ionization.
• Capillary diameter
• Blood flow.
• Fat solubility.
• Solubility.
• Size.

References

Dr. J. Bruno Montoro Rosano. Basic principles of pharmacology. Barcelona: Vall d Hebron, 2015.

Antonio Mª Rabasco Álvarez. Biopharmacy and Basic Pharmacokinetics. Barcelona: 1996, Pharmacokinetics.

Council on Family Health, “Drug interactions / Spanish” available at: https://www.fda.gov/downloads/Drugs/ResourcesForYou/UCM163357.pdf