In the modern world there is a huge amount of medicines. In addition to the fact that each of them has specific physical and chemical properties, they are still participants in certain reactions in the body. So, for example, with the simultaneous use of two or more drugs, they can interact with each other. This can lead to both a mutual strengthening of the action of one or both agents (synergism), and to their weakening (antagonism).
The second type of interaction will be discussed in detail below. So, the antagonism in pharmacology. What is it?
Description of this phenomenon
The definition of antagonism in pharmacology came from the Greek: anti - against, agon - fight.
This is a type of drug interaction, in which there is a weakening or disappearance of the therapeutic effect of one or each of them. In this case, the substances are divided into two groups.
- Agonists are those that, when interacting with biological receptors, receive a response from them, thereby exerting their effect on the body.
- Antagonists are those that are unable to independently stimulate receptors, as they have zero internal activity. The pharmacological effect of such substances is due to interaction with agonists or mediators, hormones. They can occupy the same or different receptors.
It is possible to talk about antagonism only in the case of exact dosages and specific pharmacological effects of drugs. For example, with a different quantitative ratio, a weakening or complete absence of the action of one or each may occur, or, on the contrary, their strengthening (synergism) may occur.
An accurate assessment of the degree of antagonism can only be given by plotting. This method clearly demonstrates the dependence of the relations between substances on their concentration in the body.
Types of drug interactions with each other
Depending on the mechanism, there are several types of antagonism in pharmacology:
- physical;
- chemical;
- functional.
Physical antagonism in pharmacology - the interaction of drugs with each other is due to their physical properties. For example, activated carbon is an absorbent. In case of poisoning by any chemical substances, the use of coal neutralizes their effect and removes toxins from the intestines.
Chemical antagonism in pharmacology - the interaction of drugs is due to the fact that they enter into chemical reactions with each other. This type has found great application in the treatment of poisoning with various substances.
For example, with cyanide poisoning and the introduction of "sodium thiosulfate", the process of sulfonation of the former occurs. As a result, they turn into less dangerous for the body rodanides.
The second example: in case of heavy metal poisoning (arsenic, mercury, cadmium and others), “Cysteine” or “Unitiol” are used, which neutralize them.
The types of antagonism listed above are united by the fact that they are based on processes that can occur both within the body and in the environment.
Functional antagonism in pharmacology differs from the previous two in that it is possible only in the human body.
This view is divided into two subspecies:
- indirect (indirect);
- direct antagonism.
In the first case, drugs affect different elements of the cell, but one eliminates the effect of the other.
For example: curare-like drugs (Tubokurarin, Ditilin) act on skeletal muscles through cholinergic receptors, while they eliminate cramps, which are a side effect of strychnine on spinal cord neurons.
Direct antagonism in pharmacology
This species requires a more detailed study, as it includes many different options.
In this case, the drugs act on the same cells, thereby suppressing each other. Direct functional antagonism is divided into several subspecies:
- competitive;
- nonequilibrium;
- not competitive;
- independent.
Competitive antagonism
Both substances interact with the same receptors, while acting as rivals for each other. The more molecules of one substance bind to the cells of the body, the less receptors the molecules of another can take.
A lot of drugs enter precisely into competitive direct antagonism. For example, Diphenhydramine and Histamine interact with N-histamine receptors alone, and they are competitors for each other. The situation with vapors of substances is similar:
- sulfonamides (Biseptolum, Bactrim) and para-aminobenzoic acid (abbreviated: PABA);
- phentolamine - adrenaline and norepinephrine;
- hyoscyamine and atropine - acetyl choline.
In the examples listed, one of the substances is a metabolite. However, competitive antagonism is also possible in those cases when none of the compounds will be such. For instance:
- “Atropine” - “Pilocarpine”;
- "Tubokurarin" - "Ditilin."
The basis of the mechanisms of action of many drugs is the antagonistic relationship with other substances. So sulfonamides, competing with PABA, have an antimicrobial effect on the body.
The blocking of choline receptors by Atropine, Ditilin and some other drugs is due to the fact that they compete with acetylcholine in synapses.
Many drugs are classified precisely on the basis of their affiliation with antagonists.
Nonequilibrium antagonism
With nonequilibrium antagonism, two drugs (agonist and antagonist) also interact with the same bioreceptors, but the interaction of one of the substances is practically irreversible, since after that the activity of the receptors is significantly reduced.
The second substance fails to successfully interact with them, no matter how much it tries to have an effect. This is the type of antagonism in pharmacology.
An example that is the most striking in this case: dibenamine (as an antagonist) and norepinephrine or histamine (as agonists). In the presence of the former, the latter are not able to exert their maximum effect even at very high dosages.
Noncompetitive antagonism
Non-competitive antagonism is that one of the drugs interacts with the receptor outside its active center. As a result, the effectiveness of the interaction with these receptors of the second drug decreases.
An example of such a relationship of substances is the action of histamine and beta-adrenergic agonists on the smooth muscles of the bronchi. Histamine excites H1 cell receptors, thereby causing narrowing of the bronchi. Beta-adrenergic agonists (Salbutamol, Dopamine) act on beta-adrenergic receptors and cause bronchodilation.
Independent antagonism
With independent antagonism, drugs act on different cell receptors, changing its function in opposite directions. For example, spasm of smooth muscles caused by carbacholine as a result of its effect on m-cholinergic receptors of muscle fibers is reduced by adrenaline, which relaxes smooth muscles through adrenergic receptors.
Conclusion
It is extremely important to know what this antagonism is. In pharmacology, there are many types of antagonistic relationships between drugs. This must be taken into account by doctors while prescribing several drugs to the patient and to the pharmacist (or pharmacist) when they leave the pharmacy. This will help to avoid unforeseen consequences. Therefore, in the instructions for use of any medicine there is always a separate paragraph on the interaction with other substances.