Pharmacokinetics: Absorption, Distribution, Metabolism & Excretion

Summary

This video explains pharmacokinetics, the study of how the body processes drugs, focusing on the four main components of ADME: Absorption, Distribution, Metabolism, and Excretion. It covers various drug administration routes, factors influencing absorption, and the concept of bioavailability. The video also dives into metabolism phases, including phase one (oxidation) and phase two (conjugation), as well as elimination processes. It further explores concepts like half-life, clearance, and how the body reaches steady-state drug concentrations. The video provides essential insights for understanding drug behavior in the body and its therapeutic effects.

Takeaways

• 😀 Pharmacokinetics is the study of how the body processes a drug, focusing on absorption, distribution, metabolism, and excretion (ADME).
• 😀 Absorption refers to the movement of a drug into the bloodstream via different routes such as oral, intravenous, or inhalation.
• 😀 Drug absorption is influenced by factors such as solubility, molecular weight, pH, and blood flow to the absorption site.
• 😀 Bioavailability is the fraction of an administered drug dose that reaches systemic circulation unchanged.
• 😀 Intravenous administration has 100% bioavailability because it bypasses the first-pass metabolism in the liver.
• 😀 The first-pass effect reduces bioavailability of oral drugs as they undergo metabolism in the gut and liver before entering systemic circulation.
• 😀 Drug distribution depends on factors like membrane permeability, lipophilicity, plasma protein binding, and the drug’s volume of distribution.
• 😀 Drugs with high lipophilicity and small molecular size tend to have a higher volume of distribution and are more likely to enter tissues.
• 😀 Metabolism converts drugs into active or inactive metabolites, primarily in the liver, and can be classified into phase 1 (oxidation/reduction) and phase 2 (conjugation).
• 😀 The clearance rate measures how fast a drug is eliminated from the body, and it is crucial in determining the drug's duration of effect.
• 😀 Half-life is the time it takes for the plasma concentration of a drug to decrease by 50%, and it helps in determining dosing schedules and reaching steady-state concentrations.

Q & A

What is pharmacokinetics?

Pharmacokinetics is the study of how the body processes a drug, focusing on the movement of drugs into, through, and out of the body.

What does ADME stand for in pharmacokinetics?

ADME stands for Absorption, Distribution, Metabolism, and Excretion, which are the four main components of pharmacokinetics.

How do different routes of administration affect drug absorption?

The route of administration influences how a drug is absorbed into the body. For example, intravenous drugs are absorbed directly into the bloodstream, while oral drugs must be absorbed through the gastrointestinal tract, which can be affected by factors like food and acidity.

What is bioavailability?

Bioavailability is the fraction of an administered dose of a drug that reaches the systemic circulation in an unchanged form. It is influenced by factors such as absorption rates and the first-pass effect.

What is the first-pass effect?

The first-pass effect refers to the metabolism of drugs in the gut and liver before they enter the bloodstream, which reduces the drug's bioavailability, especially for oral drugs.

What factors influence drug distribution in the body?

Factors influencing drug distribution include membrane permeability, lipophilicity (ability of the drug to cross membranes), molecular size, plasma protein binding, and the volume of distribution.

How does plasma protein binding affect drug distribution?

Plasma protein binding slows down the distribution of drugs because it reduces the amount of free (unbound) drug available to enter tissues, thereby limiting its distribution.

What are the two phases of drug metabolism?

Drug metabolism occurs in two phases: Phase 1, where the drug is oxidized or reduced to a more polar form, and Phase 2, where the drug is conjugated with a polar group to increase water solubility for easier elimination.

What is the role of cytochrome P450 enzymes in drug metabolism?

Cytochrome P450 enzymes are responsible for oxidizing or reducing drugs in Phase 1 of metabolism, making them more polar and water-soluble, which helps in their elimination from the body.

What is the difference between zero-order kinetics and first-order kinetics in drug elimination?

In zero-order kinetics, the rate of drug elimination is constant and independent of drug concentration, while in first-order kinetics, the amount of drug eliminated is proportional to its concentration in the body.