Ticket 31

1. Distribution of medicinal substances in the body. Biotransformation of medicinal substances in the body and ways of their excretion. Concept and bioavailability.

2. Narcotic (opioid) analgesics. Classification. Mechanism of action. Side effects. Contraindications Comparative evaluation of drugs. Antagonists of narcotic analgesics.

3. Laxatives. Classification. Mechanism of action. Indications for use. Side effects. Contraindications Comparative evaluation of drugs.

4. Complications arising from the use of antibiotics, measures for their prevention.

1. Distribution of medicinal substances in the body. Biotransformation of medicinal substances in the body and ways of their excretion. Concept and bioavailability.

1. After absorption, many medicinal substances nonspecifically and reversibly bind to blood plasma proteins, mainly albumin. In this case, different drugs compete with each other for the same binding zones on the surface of the protein and displace each other. Protein-bound drug fractions do not penetrate into tissues and are virtually devoid of pharmacological action. Only the free fraction of the drug in plasma has the ability to penetrate tissues and act. The binding capacity of the blood decreases significantly with protein starvation, liver diseases, extensive burns, with age, and with the replacement of blood loss with protein-free fluids. 2. A dynamic equilibrium is maintained between the free fraction of the drug and the fraction bound by proteins: as the free substance is released into the tissue, its amount is replenished due to the previously bound proteins. When administered intravenously, the following stages occur: - the preparation of the drug in the blood reaches peak concentrations and enters primarily into well-vascularized tissues (heart, brain, kidneys, lungs), which take on the toxic effect; -in the next minutes after administration, the drug is distributed throughout the entire aqueous phase, including organs with slow blood flow (skeletal muscles, subcutaneous tissue) 3. drugs with high lipophilicity are absorbed by adipose tissue, creating a depot that releases the drug as its concentration in the blood decreases brain, kidneys, lungs), which take on the toxic effect; -in the next minutes after administration, the drug is distributed throughout the aqueous phase, including organs with slow blood flow (skeletal muscles, subcutaneous tissue) 3. drugs with high lipophilicity are absorbed by adipose tissue, creating a depot that releases the drug as its concentration in the blood decreases brain, kidneys, lungs), which take on the toxic effect; -in the next minutes after administration, the drug is distributed throughout the entire aqueous phase, including organs with slow blood flow (skeletal muscles, subcutaneous tissue) 3. drugs with high lipophilicity are absorbed by adipose tissue, creating a depot that releases the drug as its concentration in the blood decreases

The significance of biotransformation lies in converting a dangerous substance into a less toxic and water-soluble substance, in order to subsequently remove them with the kidneys, bile, then (excretion routes). This goal is achieved by transferring drug molecules to more polar, more ionized, less lipophilic, less binding to plasma and tissue proteins, less penetrating through biological barriers that are not reabsorbed in the kidneys and intestines.

Biotransformation occurs in the cells of the liver, intestines, lungs, skin and blood plasma. A certain amount is excreted in the urine unchanged.

There are 2 phases of biotransformation: 1) the molecules undergo hydrolysis, oxidation or reduction. 2) When administered orally, the drug begins to undergo biotransformation already in the intestine and during the first passage through the liver, that is, before entering the systemic circulation. This stage of biotransformation is defined as first pass metabolism.

Bioavailability (bioavailability) is characterized by the fraction of the drug from the administered dose that enters the systemic circulation in an active form. Depends on: presystemic metabolism, properties of the drug form, the rate of absorption, conditions affecting the adsorption of drugs.