Routes of administration of drugs into the body

From the routes of drug in the body, its distribution and elimination depend exclusively timing of the therapeutic effect, its duration and severity. The route of administration the drug in the body due to the purpose of prescribing, view of the dosage form, Physico-chemical properties of the components, and state, physiological and pharmacodynamic characteristics of the organism, the main character and the presence of comorbidities and other indicators.

There are the following ways to the administration of drugs into the body: enteral (through blood) and parenteral (bypassing the gastrointestinal tract). When the absorption of drugs is set value of the suction surface. For comparison: area of ​​skin - 1,72 m2, light - 70 m2; total area, through which the absorption in the intestine, reaches 400-500 m2 by folds of the intestinal mucosa, the vast number of villi and microvilli.

Many drugs administered orally (through the mouth) - It is the most common method of administration, and, referring to the absorption, usually mean their transport through the membrane of epithelial cells GI, depending on the pH changes its various departments, surface area per unit volume of the suction (along the digestive tract), tissue perfusion, movement of mucus and bile, properties of the membranes of the epithelial cells. The drugs, taken orally, before you get into the blood, are two natural biological filter barrier – gastrointestinal mucosa and liver. Therefore, this route of administration of drugs is the most physiological.

However, some drug substances (benzilpenicillin, insulin and others.) destroyed in the acid environment of the stomach or by enzymes in the intestine, therefore they can be administered only parenterally.

For parenteral administration (intravenously, intraarterially, intramuscularly, subcutaneously) substance in contact with the tissues, usually, not changed. They, bypassing the biological filters, enter the bloodstream. This route of administration of drugs should be used as sparingly as possible to protect the body from foreign substances entering, can cause allergic reactions and infectious processes. Usually, the parenteral route of administration used for:

• emergency treatment, when you want to get a quick effect (eg, with pulmonary edema intravenous furosemide);
• administration of large volumes of drugs;
• prolonged administration of drugs (intravenously);
• drug administration, which may cause local tissue damage (eg, cytotoxic agents).

Vasoconstrictor and vasodilator agents promote, respectively, slowing down or accelerating absorption of drugs into the site of injection.

Intramuscular and subcutaneous drug administration does not have to penetrate through the skin, but must pass through the walls of capillaries. Due to the porosity of the capillaries major factor, determining the rate of absorption, It is a specific blood flow, however the rate of absorption of substances largely depend on the injection site. For Example, diazepam absorption when administered intramuscularly in a slightly vascularized portion may be lower, than after oral administration. Poorly absorbed in adequate conditions of poorly soluble salts of acids and bases.

For intramuscular and subcutaneous injection, aqueous and oily solutions, emulsions and suspensions. The rate of absorption depends on the nature of the solvent. The drugs are absorbed from aqueous solutions, usually, fast enough, while other drugs system (suspension, oily solutions, emulsion) provide a sustained action, that is commonly used in medical practice. For Example, when administered intramuscularly 40% solution of phenytoin sodium in propylene glycol at pH 12 proishodit absorption propylene, and tissue fluids, acting as a buffer, lower pH, shifting the equilibrium between the ionized form and the free acid. Sparingly soluble free acid precipitates, subsequent dissolution and absorption which is very slow (1-2 of the week).

Less commonly used spinal and intracranial (suboccipital, subarachnoid, subdural et al.) injection, require large medical experience. For these purposes, sterile, crystal clear true aqueous solutions of neutral. Action develops rapidly.

Medicines, input sublingual or rektalno, do not fall into the portal vein and the liver, these paths in the most rational administered drugs, are significantly destroyed during the first-pass metabolism.

The rectal route of administration is preferred for drugs, have an unpleasant taste, smell or irritating, and in pediatrics (when children are in a state of unconsciousness, We tend to vomit, moody and refuse to take medicine). When rectally administered drug reduces the possibility of unwanted side effects, especially allergic reactions. Sublingual and rectal routes of administration provide a rapid absorption of drugs (7-10 Min.).

In recent years, it has been developed Inhalation (via the respiratory tract) route of administration of drugs into the body. Inhalation any medication recommended before meals or later, 1,5 hours after meals, as the "limited" diaphragm does not allow a full breath.

The transdermal route, and the route of administration of drugs through the mucosal a great variety and are widely used in medical practice for local and general effects on the body. These methods are considered safe drug administration, since drugs are outside the body, and the dose can be changed. The surface of the suction applied medicines into ointments, Gels, creams, liniments, liquids in the form of compresses, transdermal therapeutic systems, patch, medical dressings, etc.. d. The drugs are absorbed through intact skin slightly. Their penetration is increased when applied to a wound, damaged skin, as well as the use of occlusive dressings.

Among dosage forms, applied to the mucosa, the most widely used eye drops, ointment, Polymer film, rinsing, and lotions, and sprays, nasal drops, ear drops. In this case, the efficacy of medicinal substances influenced by the same factors numerous, cited before.

Better absorption of substances promotes good blood flow to the site of absorption, as well as its state. When stagnation drugs enter the general circulation slowly and in small amounts. In this case, the route of administration elected by such drugs into the body, which provides better absorption and distribution in the body. For Example, at the stagnation in the intestine and liver it is recommended to introduce the drug sublingually or rectally.