The Pharmacodynamics or pharmacodynamics Is the study of the effects of drugs on the human body and animal or on the microorganisms or parasites present within it.
This discipline analyzes the interaction of drugs with living organisms at different levels: sub-molecular, molecular, cellular, tissue, organ and whole body.
That is, it looks at the reactions of both Cells As of the organs to understand the reaction as a whole.
Through these analyzes, pharmacodynamics allow us to know how long it takes for a drug to take effect, which part of the body will act or whether it will have any side effects.
Selectivity of action in pharmacodynamics
Selectivity is the ability of each drug to"select"the place of the organism in which it must act. Each drug has a higher or lower degree of selectivity and this is also subject to pharmacodynamic analysis.
Some drugs are applied directly in the place where their effects are required. Eye drops or ointments for the skin are examples of this.
However, most drugs enter the body by injection or by mouth. In these cases, the drug enters the system and"selects"which organs to affect. In these cases three different degrees of selectivity can be observed:
- There are drugs that are practically non-selective since their action is directed simultaneously to several organs or tissues. Atropine, for example, is geared towards the muscular relaxation of the digestive system but can also produce muscular relaxation of the respiratory system.
- Other drugs are relatively selective because their action is directed at any area that is affected. For example, Ibuprofen acts on any part of the body that has inflammation.
- Finally there are other very selective drugs, which only act on a specific organ. It is the case of digoxin, which is used for heart failure and has effect only in the heart.
Selectivity, rather than a"select"ability, has to do with the compatibility of chemical compounds with the biological structure of the organism.
Interaction with receptors and enzymes
The action of drugs depends on their interaction with certain elements of the organism. It is necessary to take into account that each medicine has particular forms of interaction with receptors and enzymes and this depends on its functioning.
The receivers
Receptors can be defined as the gateway to cells. They are molecules that are in the surface of these and only let enter those substances necessary for its normal operation.
Usually these are substances that the body naturally produce, such as hormones or neurotransmitters. These substances are compatible only with the receptors of those cells that need them to fulfill their basic functions.
The drugs perform a similar process: imitating the action of natural substances, enter the cells through the receptors. In this way they can help to inhibit or stimulate functions as the need arises.
For example, painkillers act on certain brain receptors that are designed to receive substances that control pain.
Each drug is designed to target different receptors. This is the cause of selectivity: drugs travel all over the bloodstream but only target receptors with which they have compatibility.
According to their relationship with the receptors, the drugs are classified as agonists or antagonists:
The Agonist drugs Are related to the receiver. Thanks to this they are fixed to it and in this way manage to stimulate the desired functions in the cell.
The Antagonistic drugs Are also related to the receiver. However, they are fixed to it to block it and reduce or eliminate its response
The enzymes
Enzymes are molecules responsible for regulating the rate of chemical reactions that occur in the body.
There are drugs that are not directed at the cellular receptors, but at the enzymes. These drugs have the function of increasing or slowing down certain chemical processes and are classified as inhibitors or inducers.
An example of these drugs is lovastatin, which has the goal of reducing cholesterol. This is achieved by inhibiting the functioning of the enzyme HMG-CoA reductase, which is responsible for regulating the production of cholesterol in the body.
Other pharmacological interactions
As noted, most drugs interact with receptors and enzymes to modify their natural functions.
However, there are also other types of drugs that work through physical and chemical reactions.
An example of a chemical reaction is produced by antacids, which are bases that interact with acids to neutralize stomach acids.
The action of drugs
The drugs do not create new physiological functions, they only apply changes on the functions that already exist.
They can stimulate, inhibit or accelerate these functions in order to generate specific reactions in the organism.
These actions are measured according to certain relative properties that allow to predict what the results of the use of a determined drug will be:
- Reversibility Refers to the property of the drugs to lose their binding to the receptors and allow the cell to regain its normal functioning.
- Affinity Is the mutual force of the link between a drug and a receptor. Higher affinity implies a greater effect of the drug on the cell.
- Intrinsic activity Is the ability of a drug to produce an effect when it is attached to a receptor.
- The power Refers to the amount of drug required to produce a specific effect on an organ or tissue
- The effectiveness Refers to the ability of a drug to produce a particular response.
- The effectiveness Refers to the efficacy of a drug in its actual context. For example, a drug that has side effects can be abandoned by patients and as a result loses effectiveness.
- Specificity Refers to the number of mechanisms involved. Less specific drugs are targeted at several receptors at a time to achieve the expected effect while the more specific drugs target a single receptor.
- The tolerance Refers to the adaptation of the organism to the continuous presence of a drug.
References
- All Sands. (S.F.). What Is Pharmacodynamics. Retrieved from: allsands.com
- Clinic Gate. (2015). Basic Principles and Pharmacodynamics. Retrieved from: clinicalgate.com
- Farinde, A. (S.F.). Drug Dynamics. Recovered from: merckmanuals.com
- Lees, P. (2004). Principles of pharmacodynamics and their applications in veterinary pharmacology. Retrieved from: researchgate.net
- Teuscher, N. (2010). What is pharmacodynamics? Recovered from: certara.com.