Methods and rate of administration of drugs. Isolation of medicinal substances

Ways and methods of administration medicines into the body. Their classification, general and Comparative characteristics. Factors determining the choice of route of administration and dosage form.

Routes of administration of drugs into the body are divided into enteral and parenteral.

Enteral routes provide access medicinal substances into the body throughout the gastrointestinal tract (enteros - intestinal tube).

Enteral routes include oral, sublingual, subbucal, and rectal routes of drug administration.

1. Oral (oral, ingestion, per os)

The medicine is taken orally through the mouth. Once swallowed, the medicinal substance is released from the dosage form, dissolves in the contents of the stomach or intestines and is absorbed throughout the gastrointestinal tract, enters the portal vein system, passes through the bloodstream through the liver, then into the inferior vena cava, right heart, pulmonary circulation, left heart, then into the aorta and to organs and target tissues.

This is the simplest and convenient way introducing drugs into the body. It does not require the assistance of medical personnel and both liquid and solid dosage forms can be administered in this way. Provides both systemic and local action. Based on systemic action, drugs that are well absorbed from the cavity of the stomach or intestines should be prescribed. If it is necessary to create a high concentration of the drug in the gastrointestinal tract, on the contrary, it is desirable to use medicinal substances that are poorly absorbed, which makes it possible to obtain the desired local effect in the absence of systemic adverse reactions.

The disadvantages of the oral route of administration are: relatively slow entry of the drug into the general circulation, which, in the case of a resorptive action, slows down the onset therapeutic effect and does oral route administration of drugs unacceptable in the provision of emergency care ingested drugs undergo a first-pass effect in which significant amount the drug is metabolized in the intestinal wall and in the liver before the substance reaches the systemic circulation, which leads to a decrease in its bioavailability large individual differences in the rate and completeness of absorption the effect of food and other drugs on absorption inability to use based on the systemic effect of drugs that penetrate poorly through mucosa of the gastrointestinal tract (for example, the anti-tuberculosis antibiotic streptomycin and other antibiotics from the aminoglycoside group), or those that are destroyed in the gastrointestinal tract (insulin), this method is unacceptable if the patient is unconscious, some drugs, if they oral intake can cause gastrointestinal ulcers

2. Sublingual (under the tongue)

Provides, unlike oral administration, absorption directly into systemic circulation, bypassing the portal circulation of the liver and first-pass metabolism, which makes it possible to prescribe in this way medicinal substances that are destroyed when they are taken orally (for example, the b-agonist isoprenaline).

mucous membrane oral cavity has an abundant blood supply, which ensures the rapid entry of drugs into the blood and contributes to the same rapid offensive effect. This makes the sublingual route of administration especially convenient for emergency care in outpatient settings, for example, with angina attacks (taking nitroglycerin) or hypertensive crises (using clonidine or nifedipine).

One of the main disadvantages of the sublingual route of drug administration, which significantly limits its use, is the relatively small absorption area compared to that in the intestine, which allows only highly lipophilic substances to be administered in this way. high activity.

The most commonly administered sublingual drugs are in the form of solutions, powders and tablets.

3. Subbuccal (for the cheek)

The medicine is placed between the gums and the cheek.

It is a type of drug administration through the mucous membrane of the oral cavity, so that it has the same properties as the sublingual route.

It provides a certain advantage over the sublingual method if it is necessary to prolong absorption in order to increase the duration of action, for which special dosage forms are used, for example, in the form of slowly absorbable plates (trinitrolong), which are glued to the gum mucosa. If necessary, unlike oral administration, the effect of the drug can be easily stopped by removing the drug from the oral cavity.

4. Rectal administration (per rectum)

Administration of the drug through anus into the ampulla of the rectum.

Allows you to partially avoid the effect of the first pass, although not as complete as sublingual administration (the drug from the middle and lower parts of the rectum enters the general circulation, bypassing the liver, from the upper to the portal circulation).

This route of administration can be used for vomiting, obstruction of the esophagus, decreased portal circulation, in newborns, when injections are impossible or undesirable.

To disadvantages rectal route administration of drugs include pronounced individual fluctuations in the rate and completeness of absorption, psychological difficulties and inconvenience in use.

Drugs are administered rectally in the form of rectal suppositories or enemas.

parenteral routes. The drug is injected into the body, bypassing the gastrointestinal tract.

There are injection, inhalation, transdermal routes of administration, as well as topical application of drugs.

1. Injectable (injection)

The medicine is injected into the tissues with a needle and syringe or injected directly into the blood. Thus, most of the disadvantages of enteral routes of administration are overcome: substances that are not absorbed or destroyed in the gastrointestinal tract can be introduced into the body; drugs enter the systemic circulation, bypassing the liver; drug develops, as a rule, faster and more pronounced (due to faster and more complete absorption), which may have crucial when providing emergency care.

The disadvantages of injection routes are: the technique is invasive and painful, most often the help of medical staff is needed (although self-administration is possible), the sterility of the injected drugs and compliance with the rules of asepsis are accompanied by tissue damage, and therefore, there is a risk of complications associated with this.

Intravenous administration

Aqueous solutions of drugs (more rarely, specially prepared fatty ultra-emulsions) are injected into one of the superficial veins in the area of the elbow, hand or foot, in children - the scalp. If necessary, infusion of large volumes of fluid with high speed the introduction is carried out in veins of larger diameter, for example, in the subclavian vein.

Provides direct entry of the drug into the general circulation in full (100% bioavailability), which means it ensures high dosing accuracy and contributes to the fastest onset of the effect.

The main disadvantages of the intravenous route of administration include:

the impossibility of introducing oily solutions, suspensions, which makes it difficult to use medicinal substances that are poorly soluble in water, or precipitate when added to an isotonic sodium chloride solution or glucose solution, commonly used as solvents

special skills are required for injection, so in the vast majority of cases the assistance of trained personnel is necessary

Excessively high (toxic) concentrations of medicinal substances can be created in organs with good blood supply in the first minutes after administration

With the introduction of hypertonic solutions, irritants, long-term continuous infusion, thrombophlebitis may develop and venous thrombosis, and in case of extravasation of certain drugs (calcium chloride solution, strophanthin), the appearance strong irritation tissues and their necrosis.

Intra-arterial administration

Provides the creation of a high concentration of the drug in the basin of the corresponding artery. It is used to administer, for example, thrombolytic agents, which makes it possible to create them high concentration directly in the area of the existing thrombus and, if not completely avoided, then at least weaken the manifestations of their systemic action, as well as radiopaque agents (allows to improve the visualization of the relevant organs) and drugs that are rapidly metabolized (for example, prostaglandins).

It is rarely used for the administration of other drugs, as it is potentially more dangerous than intravenous. This is due to the fact that the introduction of a drug into an artery can provoke a spasm of the vessel, cause its thrombosis and thus lead to ischemia and tissue necrosis.

Intramuscular administration

The drug is injected into the thickness of the muscle tissue of skeletal muscles, such as the gluteus maximus, quadriceps femoris, or deltoid muscle of the shoulder. Muscles are well supplied with blood, which ensures the rapid entry of drugs into the general circulation and contributes to the same rapid development effect, however, such a sharp initial increase in the concentration of the drug in the blood as with intravenous administration not observed, and therefore, the risk of associated complications is absent.

In this way, sterile isotonic aqueous and oil solutions and suspension of medicinal substances. With the introduction of oil solutions and suspensions, the absorption of medicinal substances slows down, which makes it possible to prolong the effect of the drug. For example, a single intramuscular injection of a suspension of benzathine-benzylpenicillin ensures that the therapeutic concentration of this antibiotic in the blood is maintained for a month.

Max volume intramuscular injection should not exceed 10 ml. It should, if possible, avoid the introduction of irritating substances into the muscles, as well as hypertonic solutions.

Intramuscular injections due to the need for deep needle insertion, as a rule, cannot be performed by the patient on their own.

Subcutaneous administration

Injections are carried out in loose connective tissue subcutaneous fat most often in the shoulder, thigh or abdomen. Self-administration is possible, since deep penetration of the needle is not necessary.

Due to the relatively weak blood supply, the absorption of drugs is slowed down and the pharmacological effect, as a rule, develops later than with intramuscular administration. The absorption of drugs, and therefore the onset of their effect, can be accelerated by lightly massaging the injection site or applying warm heating pad causing mild hyperemia. If it is necessary to slow down the absorption and thereby prolong the action of drugs, use the introduction of their depot forms in the form of oily solutions or suspensions.

Sterile isotonic aqueous and oily solutions and suspensions of medicines are injected under the skin in a volume of 1-2 ml. The drugs administered should not irritant and cause a sharp vasoconstriction (as, for example, norepinephrine) due to the threat of inflammation or tissue necrosis at the injection site.

In severe violation peripheral circulation, which occurs, for example, in shock, the introduction of drugs under the skin is impractical due to a sharp slowdown in their absorption.

Introduction to the spinal canal

The injection is carried out between the spinous processes, usually the fourth and fifth lumbar vertebrae. In this case, the drug can be administered epidurally (into the space between the bone canal of the vertebrae and the dura mater) or subarachnoidly (under the soft meninges). In this way, it is possible to create a high concentration of medicinal substances, including those poorly penetrating through the BBB, in the cerebrospinal fluid and brain tissues.

The main disadvantages of the method, which significantly limit its use, are complex technique procedures that require special skills and experience, limiting the amount of injected solution (usually no more than 3-4 ml) due to the threat of excessive high rise intracranial pressure, undesirability reintroduction and the risk of spinal cord injury.

2. Inhalation administration

Drugs are introduced into the body through Airways using special devices or by inhalation in the form of gas mixtures, vapors or aerosols.

This route is the main one for introducing into the body gases (nitrous oxide) and volatile liquids (ether for anesthesia, halothane, enflurane, etc.), used as general anesthetics. It ensures their rapid absorption and development of the effect due to large area surface of the alveoli. The cessation of inhalation leads to a rapid cessation of the action of such drugs.

In case of respiratory diseases inhalation route promotes the delivery of drugs directly to target tissues, which reduces the total dose of the drug administered to the body and, consequently, reduces the likelihood of side effects associated with their systemic action. In this way, for example, aerosols of bronchodilators, corticosteroids, and some antibiotics are administered. It should be borne in mind that the depth of penetration of the drug into the respiratory tract depends on the size of the particles of the drug (particles with an average aerodynamic diameter of more than 5 microns settle mainly in the pharynx, 2 - 4 microns - in the bronchi, 0.5 - 3 microns - in alveoli), inhalation technique and inspiratory airflow.

Currently, for the inhalation administration of aerosols, metered-dose aerosol inhalers (freon-containing or CFC-free, as well as breath-activated), powder inhalers (for the administration of powdered substances) and nebulizers (jet and ultrasonic) are used.

When using most metered-dose aerosol inhalers containing propellant gas, in bronchial tree no more than 20 - 30% of the administered dose of the medicinal substance is received. The rest of the drug is deposited in the oral cavity, pharynx, then swallowed and absorbed, thus determining the development of systemic effects. Powder inhalers allow you to increase the fraction of the drug that reaches the lower respiratory tract up to 30 - 50%. The optimal ratio of local and system effects achieved when using nebulizers, the aerosol in which is created by passing a powerful jet of air or oxygen under pressure through the drug solution, or using ultrasound. In this case, a suspension of the smallest particles of a medicinal substance is formed, which the patient inhales through the mouthpiece or face mask. The respiratory fraction of drugs administered by metered-dose aerosol inhalers can be increased when used with spacers. The spacer is a special camera that is worn on the head of the dosing device of the inhaler. Allows you to increase the distance between the inhaler and the patient's mouth. As a result, the drug particles have time to lose excessive speed, the propellant gas partially evaporates, and the effect of the aerosol jet on back wall throats.

3. Transdermal administration. The transdermal route involves the application of a drug to the skin to provide a systemic effect. For this purpose, ointments, patches, gels are used, as well as recently developed special dosage forms that ensure the release of the drug at a given rate, the so-called transdermal therapeutic systems(TTS/TTS).

Preferanskaya Nina Germanovna

Associate Professor, Department of Pharmacology, Faculty of Pharmacy First Moscow State Medical University them. THEM. Sechenov, Ph.D.

Magnesium sulfate, taken by adults orally (orally) at a dose of 10-30 g in ½ glass of water, is poorly absorbed (no more than 20%), causes fluid retention, increases osmotic pressure in the gastrointestinal tract, increases intestinal motility and has a laxative effect. And taken orally (on an empty stomach) 20-25% solution of magnesium sulfate, 1 tbsp. spoon 3 times a day annoying nerve endings mucous membrane of the duodenum 12, increases the separation of cholecystokinin and gives a choleretic effect. With parenteral administration of magnesium sulfate, it has a calming effect on the central nervous system, and, depending on the dose administered, a sedative, hypnotic, narcotic effect. AT large doses it has a depressant effect on neuromuscular transmission and may exhibit anticonvulsant, curariform action. Magnesium sulfate lowers the excitability of the respiratory center and in large doses can easily cause respiratory paralysis. With intravenous (slow) or intramuscular injection of 5-20 ml of 20 or 25% magnesium sulfate solution, hypotensive effect, which is associated with the presence of myotropic antispasmodic properties and a calming effect. Along with this, the drug reduces the symptoms of angina pectoris and is used to stop arrhythmias ( ventricular tachycardia and arrhythmias associated with an overdose of cardiac glycosides). It is used to anesthetize childbirth, with colic, urinary retention, and other indications.

The route of administration has big influence on the duration of the drug. With enteral routes of administration, the onset of action (latent period) and the duration of action of the drug increase in comparison with parenteral (inhalation and injection) routes. The strength of the drug also depends on the route of administration. When the same dose of the active substance is administered to the body, the effectiveness of pharmacological therapeutic effect the drug will be 5-10 times more with the intravenous route of administration than with oral administration.

All ways of introducing drugs into the human body are divided into two main groups: enteral(through the digestive tract) and parenteral(bypassing gastrointestinal tract).

To enteral routes include the administration of drugs:

inside ( oral - per os);
sublingually (sub lingua);
transbuccal (cheekly);
rectally (per rectum).

parenteral routes introductions are divided into:

injection;
intracavitary;
inhalation;
transdermal (skin).

There is a less common classification of routes of administration:

routes of administration with violation of the integrity of the skin (injections, infusions);
routes of administration without violating the integrity of the integument, this includes all enteral routes, inhalation, dermal and introduction into natural body cavities (for example, into the ear, eye, nose, urethra, wound pockets).

ENTERAL ROUTE OF DRUG ADMINISTRATION

The most common, convenient and simple way to introduce drugs into the body is ingestion(orally, per os ) . Inside you can enter various dosage forms: solid(tablets, powders) and liquid(infusions, decoctions, solutions, etc.). This method of administration is natural, for in the same way we introduce food into the body. This route of administration does not require sterilization, special training sick or medical staff. Absorption of the drug by oral administration occurs over a large area (more than 120 m 2), which, with intensive blood circulation, makes it possible to quickly absorb the active substances (15-20 minutes) and provide the necessary pharmacological effect. The introduction inside is especially convenient when long-term treatment chronic patients. When treating patients with drugs taken by mouth, it is very important to prevent possible destruction and modifying them in the stomach or intestines. Many drugs are coated with enteric coatings to avoid contact with the aggressive hydrochloric acid of the stomach. Medicinal Substances (PM) different structure and origin interact with a variety of components found in the gastrointestinal tract, including digestive enzymes and food. Therefore, it is important to know what changes the drug undergoes when administered orally under the influence of the food itself, digestive juices, and, finally, to have an idea of the effect constituent parts food for drug absorption. It is advisable to administer drugs 30-40 minutes before. before meals or 1-2 hours after it. Medications designed to improve digestion - in 15 minutes. or during meals, lipophilic (fat-soluble) drugs - after meals. It is better to drink medicines with ½ or 1/3 cup of boiled or filtered water.

Some drugs are introduced into the body to obtain a very rapid therapeutic effect. sublingually(under the tongue). The mucous membrane of the oral cavity has an abundant blood supply, so the drug is quickly and well absorbed, the effect occurs after 1-2 minutes. In this case, the drug is released and absorbed into the system of the superior vena cava, enters the general circulation, bypassing the gastrointestinal tract and liver. Can be administered sublingually easily soluble tablets, solutions, drops(on a piece of sugar), keep them in your mouth until completely absorbed (about 15 minutes). Currently, many antiseptic drugs are available in the form chewable tablets, lozenges, for example, Septolete, Lizobakt, Laripront, etc. Validol, Nitroglycerin are administered sublingually to stop angina attacks. Painkiller Buprenorphine is available in sublingual tablets under the brand name "Ednok". The disadvantage of this route of administration is the small suction surface of the oral mucosa, the irritating effect of drugs or their unpleasant taste.

With the advent of new innovative dosage forms it became possible to use LS buccal(cheekly), which ensures their prolonged effect and constant concentration in the blood. Absorbable films, cheek patches or buccal tablets, applications contain lipophilic non-polar substances, are well absorbed through the buccal muscles by passive diffusion. With the introduction of Sustabukkal, its effect is manifested in 3-5 minutes. and continues until 6 o'clock. Other examples are turbutaline sulfate buccal mucoadhesive patch, Gramicidin C buccal tablets, Loracept, etc.

AT medical practice drugs are often injected rectally(through the rectum). Absorbed in the lower part of the rectum, the drug enters the lower hemorrhoidal veins and then into the general circulation, bypassing the liver. This is especially important when prescribing drugs that break down in the liver. With the correct shallow introduction, after which the patient manages to lie down a little on his side, the absorption occurs evenly and completely. The rectal route of administration ensures maximum bioavailability and rapid pharmacological effect of the drug. However, it must be remembered that deep administration is accompanied by the entry of drugs into the superior hemorrhoidal vein and further through the portal vein into the liver. This drug undergoes first pass through the liver (first pass metabolism), inactive metabolites are partially formed and its bioavailability is reduced. Used to administer drugs by the rectal route suppositories and microclysters. This method is promising and most convenient in comparison with oral administration of drugs for young children and the elderly. He found the most wide application in pediatric, gerontological and proctological practice, with various diseases of the lower sections digestive tract(hemorrhoids, fissures anus, spastic colitis, chronic constipation). For direct action on the rectal mucosa and pararectal tissue, drugs are administered in rectal suppositories , which provides the desired local effect.

The disadvantages of the rectal route of administration include the inconvenience of administration, especially if the drug must be administered at work, on a train, on an airplane or other in public places, because it requires a special individual setting. To reduce the pronounced individual fluctuations in the rate and completeness of its absorption of the drug, it is desirable to administer it after a cleansing enema or spontaneous bowel movement. It must be taken into account that the rectum does not produce digestive enzymes, therefore, high-molecular medicinal substances of protein, fat and polysaccharide structure will be poorly absorbed in it.

Continued in MA 11/12

Pharmacokinetics

Pharmacokinetics - a section of general pharmacology that studies the processes of absorption, distribution, metabolism and excretion of drugs (that is, this is how the body acts on the drug).

Ways of introducing drugs into the body

Medicinal substances are introduced into the human body different ways. The practitioner is given full right inject the drug into the body by any known route.

The choice of the method of administration is dictated by the following three circumstances:

The patient's condition: the severity of the disease (in cases threatening patient's life, fast-acting substances are introduced).

Drug properties (solubility, rate of effect development, duration of drug action).

intuition vocational training doctor.

Traditionally, enteral and parenteral routes of administration of drugs into the body are distinguished.

Enteral routes of administration(through the gastrointestinal tract):

oral (by mouth);

sublingual (under the tongue);

buccal (“gluing” to the buccal mucosa, gums);

duodenal (into the duodenum);

rectal (into the rectum).

Parenteral routes of administration(i.e. bypassing the gastrointestinal tract) :

subcutaneous;

intradermal;

intramuscular;

intravenous;

intra-arterial;

intraosseous;

subarachnoid;

transdermal;

inhalation.

Enteral routes of drug administration

Oral(lat.peros) - the most common method of administration. About 60% of all drugs are administered orally. For oral administration, various dosage forms are used: tablets, powders, capsules, solutions, etc. When taken through the mouth, the drug goes through the following steps:

Oral cavity → esophagus → stomach → small intestine → large intestine → rectum.

The absorption of a number of substances occurs partially from the stomach (weak electrolytes that are acidic in nature - aspirin, barbiturates, etc.). But the vast majority of drugs are absorbed mainly in the small intestine (this is facilitated by intensive blood supply and a large absorption surface - ≈ 120 m 2). Absorption of drugs when taken orally begins after 15-30 minutes.

After absorption in the intestine, the drug goes through the following steps:

Small intestine → absorption → portal vein → liver (partially destroyed) → inferior vena cava → big circle blood circulation → organs and tissues (therapeutic effect).

Advantages of the method:

simplicity and convenience;

naturalness;

relative safety;

sterility, hands of medical staff is not required.

The disadvantages of the method:

slow onset of effect;

low bioavailability;

individual differences in the speed and completeness of absorption;

influence of food and other substances on absorption;

the impossibility of using drugs that do not penetrate well through the mucosa of the gastrointestinal tract (streptomycin), which are destroyed in the gastrointestinal tract (insulin, pregnin);

inability to use with vomiting and coma.

Sublingual(lat. sublingua). The mucous membrane of the oral cavity has an abundant blood supply, and substances absorbed through it quickly enter the bloodstream. The effect of sublingual administration occurs by the end of the first minute. Pathway of medicinal substances:

Oral cavity → superior vena cava system → right heart → pulmonary circulation → left heart → aorta → organs and tissues (therapeutic effect).

This method introduces some fast-acting vasodilators (nitroglycerin, validol), steroid hormones and their derivatives (methyltestosterone, pregnin), gonadotropin and other drugs that are poorly absorbed or inactivated in the gastrointestinal tract.

Advantages of the sublingual route of administration:

medicines do not work gastric juice;

do not pass through the liver.

Disadvantage: inability to use drugs with bad taste and irritant to the oral mucosa.

buccal polymer films (trinitrolong) are used, which are “glued” to the buccal mucosa or gums. Under the influence of saliva, the films melt, release the pharmacologically active substance (nitroglycerin in trinitrolong) and create a therapeutic concentration in the systemic circulation for a certain time.

Duodenal route of administration . The probe is inserted through the esophagus into the duodenum and a liquid is injected through it (for example, magnesium sulfate as a choleretic). This makes it possible to quickly create a high concentration of the drug in the intestine. Advantage - the medicine is not exposed to the action of gastric juice. But this route of administration is technically complex and rarely used.

Rectally(lat. perrectum) medicinal substances are prescribed in the form of suppositories, solutions in enemas (V- no more than 50–100 ml + the solution must be heated to 37–38 º C, otherwise a reflex to emptying may occur). The therapeutic effect with this route of administration develops after 5–15 minutes. The drug route:

Rectum → lower and middle hemorrhoidal veins (about 50% of the medicinal substance) → inferior vena cava → systemic circulation → organs and tissues (therapeutic effect).

Part of the drug is absorbed through the superior hemorrhoidal vein and enters the liver through the portal vein, where it is partially metabolized.

Advantages of the rectal route of administration:

the medicinal substance is not exposed to the juices of the digestive tract;

does not irritate the gastric mucosa;

the medicinal substance bypasses the liver (about 50%);

can be used for vomiting, in an unconscious state.

The disadvantages of the method:

inconvenience, unhygienic;

individual differences in the speed and completeness of absorption.

Medicines can be administered naturally(inhalation, enteral, dermal) and with the help of technical means. In the first case of their transportation to internal environments The body is provided with the physiological suction ability of the mucous membrane and skin, in the second it happens by force.

It is rational to divide the routes of administration of drugs into enteral, parenteral and inhalation.

Enteral gilyah involves the administration of drugs through various departments alimentary canal. With sublingual (administration of drugs under the tongue) and subbucal (administration of drugs on the buccal mucosa) routes of administration, absorption begins quite quickly, the drugs exhibit general action, bypass the hepatic barrier, do not come into contact with hydrochloric acid of the stomach and enzymes of the gastrointestinal tract. Sublingually prescribed fast-acting drugs with high activity (nitroglycerin), the dose of which is quite small, as well as drugs that are poorly absorbed or destroyed in the digestive canal. The drug should be in the oral cavity until complete resorption. Swallowing it with saliva reduces the benefits of this route of administration. Frequent use sublingual medications can lead to irritation of the oral mucosa.

The oral route of administration involves swallowing the drug, followed by its passage through the alimentary canal. This way is the simplest and most convenient for the patient, does not require sterile conditions. However, only a small part of the drugs begins to be absorbed already in the stomach. For most drugs, a weakly alkaline environment is favorable for absorption. small intestine, so when oral administration pharmacological effect occurs only after 35-45 minutes.

Ingested drugs are exposed to digestive juices and may lose their potency. An example would be the destruction of insulin and other proteinaceous drugs by proteolytic enzymes. Some drugs are affected by the hydrochloric acid of the stomach and the alkaline contents of the intestine. In addition, substances that are absorbed from the stomach and intestines pass through the portal vein system to the liver, where they begin to be inactivated by enzymes. This process is called the first pass effect. This is why, and not because of poor absorption, doses of some drugs ( narcotic analgesics, calcium antagonists) when administered orally should be significantly greater than when injected into a vein. The biotransformation of a substance during its primary passage through the liver is called systemic metabolism. Its intensity depends on the speed of blood circulation in the liver. It is recommended to take medicines inside 30 minutes before meals.

Medicines are administered inside in the form of solutions, powders, tablets, capsules, granules. To prevent the destruction of certain medicinal substances in the acidic environment of the stomach, coated tablets are used that are resistant to the action of gastric juice, but soluble in the alkaline environment of the intestine. There are dosage forms (tablets with multilayer coating, capsules, etc.) that provide gradual absorption of the active substance, which allows prolonging the therapeutic effect of the drug (retard forms of drugs).

It should be remembered that in patients (especially the elderly) with impaired esophageal motility or in those who are in horizontal position, tablets and capsules can linger in the esophagus, forming ulcers in it. To prevent this complication, it is recommended to drink tablets and capsules large quantity water (at least 200 ml). Reducing the irritating effect of drugs on the gastric mucosa can be achieved by making them in the form of mixtures with the addition of mucus. In the case of a significant irritant (or ulcerogenic) effect, drugs, especially those that require long-term course application(for example, diclofenac sodium) it is advisable to take after meals.

The introduction of drugs through the mouth is impossible or difficult during vomiting, during convulsions, in a state of fainting.

Sometimes drugs are administered duodenalally (through a probe into the duodenum), which makes it possible to quickly create a high concentration of a substance in the intestine. So, for example, magnesium sulfate is administered (to achieve a choleretic effect or with diagnostic purpose).

Rectally (into the rectum) drugs are administered in the form of suppositories (suppositories) or enemas (for adults - no more than 50-100 ml). Rectal administration avoids the irritating effect of substances on the gastric mucosa, and also makes it possible to use them in cases where oral administration is difficult or impossible (nausea, vomiting, spasm or obstruction of the esophagus). Absorbed from the lumen of the rectum, drugs enter the bloodstream through portal vein, but by the system of the inferior vena cava, thus bypassing the liver. Therefore, the strength of the pharmacological action of drugs and the accuracy of dosing with the rectal route of administration is higher than oral, which allows you to administer drugs not only predominantly local action(mistsevoanestezuyuchi, anti-inflammatory, disinfectant), but also of general action (hypnotics, analgesics, antibiotics, cardiac glycosides, etc.).

parenteral route (bypassing the alimentary canal). All types of parenteral administration pursue the same goal - to deliver faster and without loss active substance medicinal product into the internal environment of the body or directly into the pathological focus.

Inhalation Iilah is the most physiological natural ways drug administration. In the form of aerosols, substances are prescribed mainly to obtain local effect(at bronchial asthma, inflammatory processes of the respiratory tract), although most substances (adrenaline, menthol, most antibiotics) introduced in this way are absorbed and also have a resorptive (general) effect. Inhalation of gaseous or finely dispersed solid and liquid drugs (aerosols) provides almost the same rapid entry into the blood as injection into a vein, is not accompanied by injury from an injection needle, and is important in relation to children, the elderly and malnourished patients. The effect is easy to control by changing the concentration of the substance in the inhaled air. The absorption rate depends on the volume of respiration, the area of the active surface of the alveoli, their permeability, the solubility of substances in lipids, the ionization of drug molecules, the intensity of blood circulation, etc.

To facilitate inhalation use non-volatile solutions, special sprayers (inhalers) are used, and the introduction and dosing of gaseous substances (nitrous oxide) and volatile liquids (ether for anesthesia) is carried out using devices (anesthesia) artificial ventilation lungs.

Cutaneous route widely used in dermatology for direct action on pathological process. Some substances are highly lipophilic, can partially penetrate the skin, be absorbed into the blood and have a general effect. Rubbing ointments and liniments into the skin promotes deeper penetration of medicinal substances and their absorption into the blood. With ointment bases lanolin, spermaceti and pork fat provide deeper penetration of medicinal substances into the skin than petroleum jelly, since they are closer in composition to the body's lipids.

Recently, special pharmacotherapeutic systems have been developed for transdermal delivery of a medicinal substance (for example, nitroglycerin) into the systemic circulation. These are special dosage forms that are fixed with an adhesive substance on the skin and provide a slow absorption of the medicinal substance, thereby prolonging its effects.

The introduction of drugs into the conjunctival sac, external ear canal, into the nasal cavity most often involves local impact on the pathological process in the relevant organs (conjunctivitis, otitis media, rhinitis). Some drugs for local application tend to exhibit a resorptive effect (for example, m-anticholinergics and anticholinesterase agents with glaucoma).

The introduction of drugs into the body cavity is used infrequently. Antibiotics are usually injected into the abdominal cavity during surgical operations. Introduction into the cavity of the joints, pleura is advisable for the elimination inflammatory processes(arthritis, pleurisy).

Among the parenteral routes of administration of drugs, injection is common: into the skin, under the skin, into the muscle, into the vein, into the artery, subarachnoid, subdural, suboccipital, intraosseous, etc.

The introduction into the skin is used mainly for diagnostic purposes (for example, a test for increased individual sensitivity to antibiotics and local anesthetics), as well as for vaccination.

Often drugs are injected under the skin and intramuscularly. These methods are used when it is impossible to administer substances through the mouth or into a vein, as well as to prolong the PHARMACOTHERAPEUTIC effect. The slow absorption of the medicinal substance (especially oily solutions) allows you to create a depot in the subcutaneous tissue or muscles, from which it gradually enters the bloodstream and is there in the right concentration. Substances that have a significant local effect should not be injected under the skin and into the muscle, as this can lead to inflammatory reactions, the formation of infiltrates and even necrosis.

Introduction into a vein saves the time required for the absorption of drugs in other ways of administration, makes it possible to quickly create their maximum concentration in the body and obtain a clear therapeutic effect, which is very important in cases of emergency care.

Only aqueous sterile solutions of drugs are injected into the vein; it is strictly forbidden to introduce suspensions and oily solutions (to prevent vascular embolism, it is vital important organs), as well as substances that cause intense blood clotting and hemolysis (gramicidin).

Medicines can be injected into a vein quickly, slowly in a stream and slowly in a drip. More often they are administered slowly (especially in children), since many drugs tend to cause an effect too quickly (strophanthin, ganglionic blockers, plasma-substituting fluids, etc.), which is not always desirable and can be life-threatening. Rational is drip introduction solutions, usually start with 10-15 drops per 1 minute. and gradually increase the speed; the maximum rate of administration is 80-100 drops per 1 minute.

The drug, which is injected into a vein, is dissolved in an isotonic solution (0.9%) NaCl or 5% glucose solution. Breeding in hypertonic solutions(for example, 40% glucose solution), except in some cases, is less advisable due to possible damage to the vascular endothelium.

Recently, a rapid (within 3-5 minutes) administration of drugs into a vein in the form of a bolus (Greek bolus) has been used. Bolos - com). The dose is determined in milligrams of the drug or in milliliters of a certain concentration of the substance in the solution.

The introduction into the artery allows you to create a high concentration of the drug in the area of blood supply to this artery. In this way, sometimes antitumor agents. To reduce their total toxic action the flow of blood can be artificially slowed down (compression of the veins). Also injected into the artery radiopaque agents to clarify the localization of a tumor, thrombus, aneurysm, etc.

Drugs that do not penetrate the blood-brain barrier well can be injected under the membranes of the brain - subarachnoid, subdural, suboccipital. For example, some antibiotics are used in cases infection tissues and membranes of the brain.

Intraosseous injections are used if it is technically impossible to inject into a vein (for children, the elderly), and sometimes for injection a large number plasma-substituting fluids (into the spongy substance of the calcaneus).

Benefits of parenteral routes of drug administration:

1. Pharmacological effect develops rapidly (magnesium sulfate reduces arterial pressure in hypertensive crisis).

2. High dosing accuracy (mg/kg body weight can be calculated).

3. The possibility of administering drugs that are destroyed by the enteral route (insulin, heparin).

4. The drug can be administered to patients in an unconscious state (insulin in diabetic coma).

Disadvantages of parenteral routes of drug administration:

1. It is necessary to sterilize the drug.

2. Need equipment, skill of medical personnel.

3. Danger of infection.

4. The introduction of drugs often causes pain.

Electrophoresis is often referred to as bloodless injection. Anions and cations of ionized drugs are able, under the influence of an electric field, to penetrate into the body through intact skin (through sweat and sebaceous glands) and mucous membranes. Partially, they linger in tissues, bind to cell proteins and interstitial fluid, and are partially absorbed further and enter the general circulation.

Pharmacology: lecture notes Valeria Nikolaevna Malevannaya

2. Routes of drug administration

Distinguish between enteral and parenteral route drug administration. enteral route- the introduction of the drug inside through the mouth ( per os), or orally; under the tongue ( sub lingua), or sublingually; into the rectum ( per rectum), or rectally.

Taking the drug through the mouth. Advantages: ease of use; comparative safety, absence of complications inherent in parenteral administration.

Disadvantages: slow development of the therapeutic effect, the presence of individual differences in the rate and completeness of absorption, the effect of food and other drugs on absorption, destruction in the lumen of the stomach and intestines (insulin, oxytocin) or when passing through the liver.

Take medicinal substances inside in the form of solutions, powders, tablets, capsules and pills.

Application under the tongue (sublingually). The drug enters the systemic circulation, bypassing the gastrointestinal tract and liver, starting to act after a short time.

Insertion into the rectum (rectal). A higher concentration of drugs is created than with oral administration.

Suppositories (suppositories) and liquids are administered using enemas. The disadvantages of this method: fluctuations in the speed and completeness of the absorption of drugs, characteristic of each individual, inconvenience in use, psychological difficulties.

parenteral route- this is different kinds injections; inhalation; electrophoresis; surface application of drugs to the skin and mucous membranes.

Intravenous administration (in / in). Medicines are administered in the form of aqueous solutions.

Advantages: rapid entry into the blood, if a side effect occurs, it is possible to quickly stop the action; the possibility of using substances that are destroyed, non-absorbable from the gastrointestinal tract. Disadvantages: with prolonged intravenous administration along the vein, pain and vascular thrombosis may occur, the risk of infection with hepatitis B viruses and human immunodeficiency.

Intra-arterial administration (in / a). It is used in cases of diseases of certain organs (liver, limb vessels), creating a high concentration of the drug only in the corresponding organ.

Intramuscular administration (in / m). Aqueous, oily solutions and suspensions of medicinal substances are administered. The therapeutic effect occurs within 10-30 minutes. The volume of the injected substance should not exceed 10 ml.

Disadvantages: the possibility of the formation of local soreness and even abscesses, the danger of accidentally entering the needle into a blood vessel.

Subcutaneous administration. Enter water and oil solutions. Do not inject subcutaneous solutions of irritating substances that can cause tissue necrosis.

Inhalation. Gases (volatile anesthetics), powders (sodium cromoglycate), aerosols are administered in this way. Inhalation of an aerosol achieves a high concentration of a medicinal substance in the bronchi with a minimal systemic effect.

Intrathecal administration. The drug is injected directly into the subarachnoid space. Application: spinal anesthesia or the need to create a high concentration of the substance directly in the CNS.

Local application. For getting local effect drugs are applied to the surface of the skin or mucous membranes.

electrophoresis It is based on the transfer of medicinal substances from the surface of the skin to deep-lying tissues using galvanic current.

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