2 Answers

  1. As always, I will not be brief and start with the preface, sorry:^)

    Overdose is an excess of the dose. For most medications, the following settings are set::

    • higher single doses (above which it is dangerous to take a single dose),
    • higher daily doses (above which it is dangerous to take a total of one day);

    — for most other substances (including some medications):

    • maximum permissible concentrations (above which ingestion from a particular object or environment is dangerous),
    • toxic doses (at which the first signs of poisoning occur),
    • semi-lethal doses (at which half of the subjects die).

    — these data are not taken out of thin air — they are established experimentally as a result of a number of tragic circumstances or during an animal experiment.

    The dose as the maximum concentration of a substance entering the body and being in it does not occur in a vacuum — it has a physiological basis:

    • On the one hand, substances are distributed throughout the body, along sensitive tissues and organs (the affinity of a substance to a tissue depends on its physical and chemical characteristics; in short, similar to similar: fat-soluble substances accumulate in fat-rich organs, and so on);
    • On the other hand, substances are processed in the body and removed from it.

    — both are carried out at a certain speed to a certain extent, and those who are interested can read more deeply about zero-and first-order kinetics (explaining this in my own words here, I will deviate too much from the topic).

    Processing of substances is carried out to a greater extent by the liver (liver cells, hepatocytes) and often by those tissues into which substances penetrate. Recycling is carried out for two purposes:

    1. to reduce the toxicity of the substance,
    2. to speed up its removal.

    The essence of recycling is to change the chemical structure of a substance-to deprive it of certain radicals or supplement it with them. As a result of processing, the physical and chemical properties of the substance change, its distribution in the body changes, and it goes to the kidneys or intestines, from where it is clearly removed. In most cases, everything ends well if the products of metabolism are not even more toxic substances, as in the case of methanol and its product damaging the optic nerve —formic acid.

    Processing, both in the liver and in other cells, is a chemical reaction, as mentioned above. Chemical reactions also represent the effects of substances on cells. In any chemical reaction, as is known (from the school course, who bothered to study it at all), substances turn one into another, most often reversibly, but due to the constant circulation through the body, it is rather irreversible. In order to transform a foreign substance, you need to use a substance from the body itself. Thus, the substances of the body's defense systems are wasted on neutralization reactions of substances coming from outside, and this pool is not infinite.

    The dose is determined precisely by how many molecules of the substance and the time they stay in the body is enough for the pool of the very substances involved in neutralization (those interested can read about the P450 cytochrome family). For ethanol, we have specific recycling systems (thank you, evolution!), but not for methanol, and they are only slightly suitable for processing alcohol isomers. We have absolutely nothing for metal poisons. Etc.

    If neutralization is ineffective, all xenobiotics (foreign substances) begin to enter the body's metabolic pathways, disrupting the natural course of things, forming even more toxic metabolites and entering into undesirable reactions with cell molecules, leading to disruption of their functions. �It is the organs in which the substance accumulates and/or is transformed to a greater extent that are affected (see above). Therefore, psychotropic substances mainly affect the brain, metal poisons muscle and bone tissue, and any substances — the liver.

  2. The principle laid down by Paracelsus is sola dosis facit venenum.

    If the highest single dose or the highest daily dose is exceeded ,the “medicine” begins to carry a toxic effect, has an unnecessary effect on the body.

    The bottom line is that drugs can not only affect certain systems, they also affect others, and more often either neutrally or negatively (see the list of side effects)

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