Medicines (medicines). The origin of the drugs are divided into the following groups: 1) products of chemical synthesis; 2) products of vital activity of microorganisms (antibiotics, certain vitamins); 3) substances of plant origin (from medicinal plants);
4) substances of animal origin (hormone, enzyme preparations);
5) substances obtained from inanimate nature (minerals, products of processing of coal, oil and so on). The mechanism of therapeutic or preventive actions drugs can be divided into two large groups: some people have this action by changing the roles of certain Fiziol. systems of the body, others destroying microbes and parasites - pathogens. In the first case we speak of pathogenetic, in the second - about etiotropic therapy.
The effects of drugs is a result of their interaction with certain biochemical (reactive) structures of the organism, which leads to the change of flow of biochemical processes, as well as the functions of the relevant tissues and organs. Depending on the nature of chemical structure L. react with certain reactive structures, and as the last character in different tissues and cells the same, then L can provide election or pre-emptive action on certain tissues and cells. For the same reason L. acting on pathogens, selectively kill or inhibit the reproduction of some species of microbes and parasites, and almost no effect on other species.
As a rule, medicinal substances form with biochemical structures of the body weak ties (electrostatic, van-der Waals, hydrogen). Therefore, the effects of drugs reversible. Only in some cases the pharmacological substance (for example, alkylating antineoplastic agents, some of organophosphorus compounds) forms with reactive structure strong covalent bonds; L. valid until, until the biological resynthesis relevant reactive structures.
Types of action of medicines. Action L., manifested before the suction it in the blood, called the local (prerecording), after absorption - resorptive. The direct effect of drugs called effect that is a direct result of exposure HP jet structure. Due to the relationship between the individual authorities change the function of any of them, as a rule, leads to a more or less pronounced changes in other organs and Fiziol. the systems of the body. Therefore, the direct action of the drug is accompanied indirect effects, or secondary reactions to drugs, the effects of the organs and systems, not directly exposed to drugs. For the occurrence of indirect actions L. typical reflex mechanism. In such cases, the indirect effects are called reflex action L.
Along with the desired action L. may cause unwanted effects - side effects, which can be different depending on the chemical nature of the drugs and peculiarities of their interaction with the body. Among the severe side effects of L. is their teratogenic effects on the fetus, which may occur when prescribing to pregnant women and is a violation of the process of Foundation and development of tissues and organs of the fetus, leading to congenital malformations (see Embryopathy). Teratogenic properties L. became known recently and still poorly understood; therefore, during pregnancy, especially in its initial period, should be used cautiously L., especially if their application is no serious evidence.
Ways of introducing drugs into the body. Resorptive effect of drugs can be achieved enteral or parenteral their introduction. The main enteral ways - ingestion and introduction through the rectum. The ingestion all vsosavchegosa L. comes primarily in the liver, where it can undergo chemical transformations. At absorption of rectal L. partially goes through the system of portal vein to the liver, and partly through the inferior Vena cava directly to the heart. Thus, in this way of introduction part that absorb the medicine gets into the blood system without preliminary chemical transformations in the liver. Parenteral methods of administration (hypodermic, intramuscular, inhalation, IV and others) provide a faster absorption and higher concentration of L. in the blood.
Ways of introduction to HP to achieve their local actions are very diverse: medications applied to the skin, give kongungualny bag into the cavity of the nose, the ear canal, vagina, rectum, is inside (for example, astringent, laxatives, and so on), injected subcutaneously (for example, a local anesthetic substance), in the cavity of the joints, in serous cavity, into the subarachnoid space, and so on, it Should be borne in mind that in applying L. in order to achieve local action, and sometimes get resorptive effects, up to the phenomena of poisoning. The intensity of pharmacological reactions both at local and resorptive effect depends on the concentration of L. in the immediate vicinity of reactive structures with which it interacts. When resorptive effect of this concentration is primarily dependent on the dose imposed.
The selection of drugs. The selection of drugs from the body occurs mainly through the kidneys. The rate of excretion by the kidneys different HP unequal. As a rule, lipitoradverse L. longer linger in the body due to the greater of reabsorption in the renal tubules. In contrast, little soluble in lipids and well-soluble in water L., especially highly dissolvine substances relatively quickly leave the body, as they are less exposed reabsorption in the renal tubules. The most rapidly excreted from the body of medications that are active excretion renal tubular epithelium (e.g. penicillin). Some HP also highlighted the glands of digestive tract, and can be re-absorbed from the gut (for example, morphine, mercury compounds, fenolftalein, and others). Volatile substances are allocated through the respiratory tract with exhaled air. Practically it is important that HP also highlighted the Breasts; this should be considered when prescribing lactating women.

Transformation of drugs in the body. Chemical transformations L. occur mainly in the liver. As a rule, the transformations are lipitoradverse substances. At that produced products with more polar structure, which is why they are less than the original L., are reabsorption in the renal tubules and quickly leave the body. Thus, the body's ability to undergo chemical transformations of medicinal substance is a private demonstration produced in the process of evolution devices to accelerate the allocation of alien substances coming into it from the environment. Chem. turning L. kataliziruetsa enzymes low specificity contained mainly in mikrosomah liver cells. In most cases, chemical transformations L. lead to their inachtivirovnie, however, often as a result of these transformations medication buy pharmacological activity (for example, chemotherapy drugs from a number of arsenobenzene, bigumal, phenacetin, and others).
Sensitivity to L. depends on a number of factors, of which almost the most important age. Children are generally more sensitive to L. than adults, and to achieve the pharmacological reactions of the same intensity children with sufficient smaller dose HP (per 1 kg of body weight)than adults. The higher the sensitivity of children to L. depend on Fiziol. regulations in the child's body: in children less perfect compensatory mechanisms that align changing functions, developing under the influence of L. In children below the activity of enzymes of a liver microsomes that are involved in chemical transformations of drugs. In respect of HP which are not exposed in the body of chemical transformations, the sensitivity of children approaching sensitivity adults. Some pharmacological agents, in particular to substances that cause hypoxia, children are less sensitive than adults.
Sensitivity to many L. (hypnotic, analgesic media group morphine, to nitroglycerin, laxative, and so on) is lowered by their re - introduction of so-called addictive. Getting used to Leningrad, acting on the higher nervous activity, often accompanied by painful addiction. L., which long remain in the body (for example, long acting barbiturates, bromine, heart glycosides from digitalis and others), during the repeated application accumulate in gradually increasing concentrations that can lead to toxic complications. This phenomenon is called by a cumulation.
Some people observed idiosyncrasy (see) to certain HP, for example to iodine, aspirin, some antimalarial drugs and so on, When usual doses cause inflammation of mucous membranes, skin rashes, hemodynamic disorders, hemolysis, and so on (see Drug disease).
By the combined action L. often use their synergies, i.e. the action in one direction, thereby strengthening the therapeutic effect. Particularly valuable when this option synergy - augmentation (synergies, where the effect of combined effect of HP more than the sum of the effects of each component taken individually). To eliminate side effects L. sometimes use the phenomenon of antagonism medicinal substances, in which one HP prevents the action of another. So, in the treatment of epilepsy phenobarbital to address the nutritional effect of the drug it is sometimes prescribed in combination with caffeine or amphetamine, which are antagonists of phenobarbital as a hypnotic, but do not prevent him antiepileptic action. Especially often antagonism of drugs used in the treatment of acute poisoning.