As noted in Chapter 2, the most important thing that determines the effect of a substance entering the body is its quantity (these are components 1 and 2 in table 4-1). Pharmacology dose is determined on the basis of human weight, because the body of a larger person contains more fluid than the body of a smaller one. Consequently, if two such people take the same amount of a drug, then its concentration will be lower in the body (and, accordingly, in the organ on which this substance acts) of a larger person. The greater the content of the drug in one or another part of the body, the, as a rule, the stronger the effect. Therefore, the amount of the substance taken should be accurately calculated based on the weight of the person.
First, determine the desired dose of the drug in milligrams per kilogram of human weight. Then the patient is weighed. Then it is easy to calculate the desired dose for this person. For example, if the required dose is 0.8 mg / kg, a person weighs 80 kg, then he should be given 0.8 x 80 = 6.4 mg of the drug.
Methods of administration
In pharmacology, the expression “method of administration” means exactly how the substance enters the body. The strength of the substance (component 3 of table 4-1) largely depends on the method of administration. In this section, we will discuss eight ways. These are the five most common: oral administration, injection (includes three types – subcutaneous, intravenous and intramuscular) and inhalation. Three other important ways are intranasal (inhalation), sublingual (placement under the tongue) and transdermal (through the skin).
Orally. Swallowing is probably the most familiar way to take medicine. Such drugs come in the form of pills, capsules, powders, liquids. These are a variety of headache medications, cough syrups, cold pills, etc., that are available in every pharmacy. Virtually all of the most affordable medicines are taken by mouth. This is the safest, most convenient, and economical way to take medicine.
After ingestion, the substance enters the stomach and is absorbed in the small intestine. Both the speed and the strength of its action depend on how the substance makes this way. The main factor determining the final effect is the food that is in the digestive tract during the intake of the substance. The more food, the slower the stomach is emptied, and in addition, it can reduce the concentration of the drug. As a result, absorption begins late, and the level of the substance in the blood is low. (This result is clearly noticeable if you compare the degree of intoxication from drinking alcohol after a heavy meal and on an empty stomach.) In addition, food can envelop the substance, and it will be released from the body along with feces. Finally, the substance taken by mouth is absorbed by the blood more slowly than if taken in other ways.
Thus, the advantages of ingestion through the mouth (comparative safety, convenience and economy) are balanced by disadvantages – a long time before absorption and a low efficiency. Moreover, gastric acids released during digestion partially destroy some substances, in particular, heroin. Once in the blood, such altered substances pass through the liver, the main organ responsible for the metabolism of most substances, and therefore only a small part of the substance reaches the brain, which inevitably reduces its effect.
Injection. The basis of the three other most common methods of drug intake is an injection of a substance using a syringe. They are usually dissolved beforehand in a liquid (“carrier”) or mixed with it. Methods of administration associated with the injection of substances subcutaneous, intravenous and intramuscular. Subcutaneous intake Injecting a substance under the skin is the simplest of these three methods, since it suffices to pierce the skin with a needle. This method is used by many novice drug addicts. It is also used in medicine for the introduction into the body of substances that do not irritate tissues (because substances introduced in this way are absorbed gradually and slowly, although faster than when taken by mouth). You can pick up a carrier fluid with which the substance is absorbed into the blood the fastest.The subcutaneous route of administration is not suitable in two cases: if the substance is irritating to the tissue and if too much solution is required to obtain the desired effect.
Intramuscular intake. In order to inject a substance into a muscle, a deeper needle penetration is needed than with a subcutaneous injection. But if the substance injected in this way is dissolved in water, and there is intensive blood circulation in the muscle, it is absorbed faster. The rate of absorption depends on which muscle group is injected. It is also influenced by the type of carrier fluid in which the substance is dissolved. The lack of an intramuscular injection is that it causes pain at the injection site. In addition, such an injection should be done by a specially trained person, otherwise there is a high risk of blood poisoning and tissue damage.
Intravenous intake. This method removes most of the problems associated with absorption. The solution of the substance is injected directly into the vein, and it begins to act immediately. Therefore, this method is used in the provision of emergency medical care. You can enter the exact dose needed by this person. In addition, irritating substances can be administered intravenously (as well as irritating “carriers”), because the walls of blood vessels are relatively insensitive, and the substance also dissolves in the blood.
The benefits of intravenous administration are obvious. The main reason for its relatively rare use is that it is more likely to be associated with possible complications, because a large amount of the substance reaches the target organ very quickly. Another consideration is that if a substance is injected through a vein for a long time, it should be strong and healthy. In general, intravenous injection is associated with the risk that it should be done slowly and monitor the patient’s response. Of course, these requirements are met in a medical institution, but it is unlikely that the same thing happens where people take drugs.
People who regularly take heroin, cocaine or their mixture (“speedball”) intravenously are often referred to as “well-established” drug addicts. They inject the drug into the vein because they want immediate and strong action. The usual dangers of intravenous use in combination with the sudden strong effect of the drug cause a great deal of damage to human health. Today, the fatal outcome of intravenous drug use is common among drug addicts.
To prevent infection by diseases such as AIDS, hepatitis, or tetanus, sterile needles and solutions should be used when injecting drugs intravenously. Drugs introduced into the body in any of the three methods of injection bypass such protective mechanisms as the skin and mucosa. Thus, pathogenic microorganisms that the body cannot neutralize can be brought in with a dirty needle or non-sterile solution. Therefore, street addicts are at great risk of contracting AIDS.
Inhalation. Some drugs can be absorbed through the membranes of the lungs. With inhalation of such drugs, the desired effect is achieved quickly (faster than with subcutaneous or intramuscular injection). In order for the drug to be inhaled, it must be in a certain state. Inhalation is applicable to drugs that can be brought into the gaseous state. For example, you can inhale substances that are components of ordinary and affordable industrial products. Such substances with psychoactive properties are called inhalants. This, for example, benzene, toluene and ligroin. You can inhale drugs that are intended for use in the form of drops. Moreover, it is possible to inhalate a mixture of gas and narcotic with small particles. These are tobacco smoke and crack crack. Inhalation of the drug gives almost complete and rapid absorption.The disadvantage of inhalation is that only small amounts of the substance can be taken at a time.
Inhalation. A powder drug is inhaled through the nose. It is absorbed through the nasal mucosa and sinuses. Cocaine, heroin and snuff are usually taken in this way. Inhalation through the nose is a good way to quickly and completely absorb poorly soluble substances. True, if you inhale an annoying drug, it can disrupt blood circulation and cause serious harm. In this regard, we can give an example of the destructive effects of cocaine on the nasal septum and nasal tissue.
Dissolving under the tongue. A tablet of substance is placed under the tongue and dissolves with saliva. The substance is absorbed through the mucous membrane of the oral cavity. In this way, nitroglycerin is usually taken, used to relieve pain in the heart. This way you can take nicotine in the form of tobacco gum or “raw” powder.
Intake under the tongue gives a faster and more complete absorption of the substance than ingestion. In addition, this way you can take drugs that irritate the stomach and cause vomiting. In the form of pills, you can use almost any substance with narcotic properties. However, this method is less popular than one would expect, because many drugs have an unpleasant taste.
- One of the safest, most convenient and cost-effective ways to receive.
- The presence in the stomach of food slows down the absorption and reduces the amount of substance entering the blood.
- Gastric acids destroy some drugs, and thus reduce their effect.
- Subcutaneous injection
- The easiest of the three methods of injection.
- Absorption is faster than when taken by mouth, but slower than with other types of injections.
- A good way to take drugs that do not irritate the tissues, because they dissolve slowly and gradually, and the substance has a lasting effect.
- The method cannot be used if the substance is irritating to the tissue, or if a large volume of fluid is to be injected.
- Intramuscular injection
- It requires a deeper penetration into the tissue, but with proper preparation of the solution and the choice of a site with an intensive blood circulation for injection, it gives a faster absorption.
- Causes pain at the injection site.
- The use of this method by people without special training is associated with the risk of blood poisoning or tissue damage.
- Intravenous injection
- Gives the fastest absorption of all methods of administration.
- The substance has an immediate effect, so the method is good for emergency medical care.
- Since the substance acts immediately, you can enter the exact dose needed by a particular person.
- The best method of injection is for receiving irritating tissue drugs, since the walls of blood vessels are relatively insensitive, and the drug is further dissolved in the blood.
- Associated with the potential danger that a large amount of the drug will immediately reach the scene of action.
- Frequent use of this method requires healthy and strong veins.
- In order to avoid complications, the dose of the substance should be introduced gradually and following the reaction of the person.
- If the drug can be inhaled, it is absorbed almost completely and faster than with subcutaneous or intramuscular injection.
- At one time you can not enter a large number of substances.
- Inhalation through the nose
- If the drug is poorly soluble, it is the best way to take it.
- Inhalation of a drug that irritates tissue or interferes with blood circulation can cause serious harm.
- Dissolving under the tongue
- In principle, this method can take almost any drug (in the form of pills).
- The substance is absorbed faster and more fully than when ingested.
- A good way to take drugs that irritate the stomach and cause vomiting.
- The method is applied less frequently than is possible, since many drugs have an unpleasant taste.
- Through the skin
- Alternative to ingestion through the mouth, if the substance is bad for the digestive tract.
- Many substances cannot be taken in this way, since their skin is relatively poorly permeable.
- You can speed up absorption by choosing places with the best skin circulation, and improve the penetration of the drug through the skin by mixing it with another substance.