In medicine, this method usually replaces the ingestion, if the substance can adversely affect the digestive tract. Acceptance through the skin is not particularly effective for most drugs, because the skin is a barrier to many chemical compounds and is relatively impermeable. But there are drugs that freely penetrate even through intact skin, and for them this method is quite applicable.
The absorption of drugs through the skin can be accelerated by selecting those parts of the body where the skin circulation is strongest. In addition, to improve the penetration of the drug can be mixed with other substances (for example, to make an oil mixture). In the form of a patch, you can take nitroglycerin – this removes the problem of the metabolism of a substance before it reaches its destination.
The choice of method depends on the properties of a particular substance, the purpose of its reception, as well as the advantages and disadvantages of a particular method of taking this substance in these circumstances. In tab. 4-2 are the main considerations for the eight drug intake methods that we discussed above. Table 4-3 shows the intake methods used for some substances.
Absorption of a drug 15
Absorption can also be defined as the rate and extent of a substance leaving a place where it was introduced. It is very important for the action of the drug. Absorption and the factors inactive on it are extremely important because they affect bioavailability. This is the part of the dose taken, reaching the place of its action or falling into the liquid, which will transfer it to its destination. Thus, the bioavailability of a drug is directly related to its effect.
Differences in the rate of absorption for different methods of administration are determined by many factors. Let’s give some examples. In all cases, except for intravenous injection, the drug must pass through at least one of the shell before it begins to spread throughout the body. Since shells are mainly composed of lipids (fats), those drugs that are better dissolved in fats are absorbed much faster. Alcohol is an example of a fat-soluble drug. Another factor is the form in which the drug is injected: it is absorbed faster in aqueous solution than in suspension, in a fat mixture or in solid form. This is due to the fact that in the state of an aqueous solution, it is already completely ready for absorption. The solubility of a substance taken in solid form depends on the conditions in the part of the body where absorption takes place. For example,Aspirin is practically insoluble in the acidic environment of the stomach, which limits the possibility of its absorption. The condition of the digestive tract affects the absorption of substances ingested through the mouth. Strong blood circulation in the place of absorption accelerates it. Finally, the area of the absorbing surface matters: the larger it is, the faster the substances are absorbed into the blood.
The factors affecting absorption are many, and they can act separately or all at once. Therefore, it is very difficult to accurately determine the effect of a drug on a person in certain conditions and at a certain time. Intravenous injection is the most effective way to deliver a drug to the site of its operation: the drug immediately connects with blood, the main element in the distribution system of substances in the body, and therefore many factors that delay absorption do not work.