Farmacocinética - Absorção, Distribuição, Biotransformação e Eliminação (Farmacologia) - Bio Aulas

Summary

In this video lesson, the concept of pharmacokinetics is explored, explaining what the body does to drugs. Key stages of pharmacokinetics are discussed: absorption (how drugs enter the bloodstream), distribution (how they are transported through the body), metabolism (how they are processed in the liver), and elimination (how they are excreted). The video also covers factors that influence absorption, such as lipid solubility, pH, and blood flow, as well as how the bioavailability of drugs is affected by metabolism and solubility. The lesson provides a comprehensive overview of how drugs move through and are processed by the body.

Takeaways

• 😀 Pharmacokinetics studies what the body does with a drug, while pharmacodynamics studies what the drug does to the body.
• 😀 Absorption is the transfer of the drug from its site of administration to the bloodstream, and it is not required for intravenous administration as the drug is directly placed in the bloodstream.
• 😀 Lipid-soluble drugs are more easily absorbed, as they can pass through the lipid membranes of cells more effectively than water-soluble drugs.
• 😀 The three main types of transport for drug absorption are passive diffusion, active transport, and endocytosis.
• 😀 Passive diffusion occurs along the concentration gradient, meaning the drug moves from a higher concentration to a lower one without energy input.
• 😀 Active transport requires energy (ATP) and works against the concentration gradient, transporting drugs from a lower to a higher concentration area.
• 😀 Endocytosis occurs when a drug molecule is too large to pass through the membrane and is absorbed by the cell via engulfment.
• 😀 Various factors influence absorption, such as pH, blood flow, surface area, and the presence of food or proteins like P-glycoprotein that may pump the drug out of cells.
• 😀 Bioavailability refers to the fraction of the drug that reaches systemic circulation after administration, with factors like first-pass metabolism affecting its amount.
• 😀 Drugs are typically distributed through the bloodstream, often binding to proteins like albumin to help transport them throughout the body.
• 😀 Biotransformation (or metabolism) primarily occurs in the liver, where drugs are chemically altered to become more water-soluble for elimination through urine or other means.

Q & A

What is the main difference between pharmacokinetics and pharmacodynamics?

Pharmacokinetics studies what the body does to a drug, such as absorption, distribution, metabolism, and elimination, while pharmacodynamics studies what the drug does to the body, including its effects and mechanisms of action.

What happens during the absorption of a drug?

Absorption is the process where a drug moves from its administration site into the bloodstream, allowing it to be transported to its site of action. This process is vital for most drug administrations, except when administered intravenously.

Why is the lipophilicity of a drug important for its absorption?

Lipophilic (fat-soluble) drugs are better absorbed because they can more easily pass through the lipid layers of cell membranes. In contrast, hydrophilic (water-soluble) drugs face more difficulty in this process.

How does passive transport differ from active transport in drug absorption?

Passive transport occurs without the use of energy and moves drugs from areas of higher to lower concentration. Active transport, on the other hand, requires energy to move drugs against a concentration gradient.

What role do the gastrointestinal pH and drug ionization play in absorption?

The pH of the environment affects whether a drug is in its ionized or molecular form, which impacts absorption. Weak acids are better absorbed in acidic environments, while weak bases are more easily absorbed in basic environments.

What is meant by 'bioavailability' of a drug?

Bioavailability refers to the fraction of the administered drug that reaches the bloodstream after absorption. It can be affected by factors such as metabolism and the method of administration.

What is the first-pass effect in drug metabolism?

The first-pass effect occurs when a drug administered orally is partially metabolized by the liver before it reaches the systemic circulation, reducing its bioavailability.

What are some factors that influence drug distribution in the body?

Factors such as blood flow, protein binding, and the ability to cross barriers like the blood-brain barrier can affect how a drug is distributed in the body.

What happens during the biotransformation or metabolism of a drug?

During metabolism, drugs are chemically altered in the liver to make them more water-soluble, often through oxidation, reduction, or conjugation, to prepare them for elimination.

How do kidneys contribute to drug elimination?

The kidneys filter drugs from the blood through glomerular filtration, secretion, and reabsorption processes. Lipophilic drugs may be reabsorbed, while hydrophilic drugs are typically excreted in urine.