Summary of "جلسه دوم فارماکولوژی قسمت اول"

Summary of "جلسه دوم فارماکولوژی قسمت اول" (Pharmacology Session 2, Part 1)

This video is a lecture on the general principles of pharmacology, focusing primarily on Pharmacokinetics and an introduction to Pharmacodynamics. The instructor explains how drugs interact with the body and how the body affects drugs, covering key concepts and mechanisms involved in drug absorption, distribution, metabolism, and excretion.

Main Ideas and Concepts

1. Introduction to Pharmacology Branches

Pharmacology has two main branches:
- Pharmacokinetics: How the body affects drugs (absorption, distribution, metabolism, excretion).
- Pharmacodynamics: How drugs affect the body (to be discussed later).

2. Pharmacokinetics: Four Main Phases

A. Absorption

Definition: Movement of a drug from the site of administration into the bloodstream.
Factors affecting absorption:
- Route of administration: IV, oral, topical, etc., affect absorption rate and extent.
- pH and ionization: Drugs are absorbed better in their non-ionized (non-polar) form because absorption membranes are phospholipid bilayers favoring fat-soluble compounds.
  - Acidic drugs absorb better in acidic environments (e.g., stomach).
  - Alkaline drugs absorb better in alkaline environments (e.g., intestines).
- Concentration gradient: Higher drug concentration at the site increases absorption.
- Blood flow: Greater blood flow at the absorption site enhances drug absorption (e.g., intramuscular > skin).
- Drug Formulation: Tablets, capsules, powders, suspensions, and solutions differ in dissolution and absorption rates.
Bioavailability: Percentage of administered drug reaching systemic circulation unchanged.
- Oral drugs often have less than 100% bioavailability due to First-pass Metabolism in the liver.
- IV administration provides 100% bioavailability initially.
First-pass Metabolism: Drugs absorbed from the GI tract enter the portal vein and pass through the liver where some are metabolized before reaching systemic circulation.

B. Distribution

Movement of drug from bloodstream to tissues.
Mainly by diffusion along concentration gradients.
Influenced by:
- Blood flow to tissues.
- Binding to plasma proteins (e.g., globulins) which retains drugs in circulation.
- Tissue affinity (e.g., anesthetics accumulate in fat, Tetracyclines in bone).
- Anatomical barriers such as the Blood-brain Barrier and placental barrier limit drug distribution to certain sites.

C. Metabolism

Primarily occurs in the liver.
Main metabolic reactions: oxidation and conjugation.
Produces metabolites:
- Polar metabolites: water-soluble, excreted by kidneys.
- Non-polar metabolites: excreted via bile into feces.
Metabolism affects drug activity and elimination.

D. Excretion

Removal of drugs/metabolites from the body.
Main routes:
- Kidneys (excrete polar/water-soluble compounds via urine).
- Liver (excretes non-polar compounds via bile/feces).
- Minor routes: lungs, sweat glands, hair follicles.
Reabsorption can occur in renal tubules, especially for lipid-soluble drugs.

3. Half-Life of Drugs

Defined as the time required for the drug concentration to reduce by half in the body.
Factors increasing Half-Life:
- Decreased renal plasma flow (less excretion).
- Increased plasma protein binding (less free drug available for metabolism).
- Decreased liver metabolism (slower drug breakdown).
Half-Life influences dosing intervals and drug accumulation.

4. Pharmacodynamics

To be discussed in a future session. Focuses on drug effects on the body.

Methodology / Key Points Summary (Bullet Format)

Pharmacokinetics Phases:
- Absorption:
  - Drug entry into bloodstream.
  - Influenced by route, pH, ionization, concentration, blood flow, formulation.
  - Bioavailability affected by First-pass Metabolism.
- Distribution:
  - Drug movement to tissues.
  - Influenced by blood flow, protein binding, tissue affinity, barriers.
- Metabolism:
  - Mainly liver-based.
  - Produces polar and non-polar metabolites.
- Excretion:
  - Mainly renal (polar drugs) and biliary (non-polar drugs).
  - Minor routes include lungs and sweat.
Drug Formulation Impact:
- Tablets/capsules require disintegration and dissolution.
- Powders dissolve faster.
- Solutions/suspensions absorbed directly.
First-pass Effect:
- Oral drugs metabolized in liver before systemic circulation.
Half-Life Determinants