Pharmacokinetics Overview

Definition: The study of how drugs are absorbed, distributed, metabolized, and excreted in the body.
Four Key Processes:
1. Absorption:
  - Process by which drugs enter the bloodstream.
  - Factors influencing absorption:
    - Route of administration (oral, intravenous, etc.)
    - Drug formulation (liquids vs. solids)
    - Gastrointestinal pH
2. Distribution:
  - Refers to how drugs disseminate throughout the body's tissues and fluids.
  - Influencing factors:
    - Blood flow to tissues (high in liver, kidneys, and heart)
    - Drug binding to plasma proteins (e.g., albumin)
    - Lipophilicity (fat solubility) vs. hydrophilicity (water solubility)
3. Metabolism:
  - Chemical alteration of a drug by the body, primarily in the liver.
  - Phase I reactions: oxidation, reduction, hydrolysis.
  - Phase II reactions: conjugation to enhance water solubility.
4. Excretion:
  - Elimination of drugs from the body, mainly via kidneys (urine).
  - Other routes: bile (feces), sweat, saliva, and milk.
  - Clearance: measure of the rate at which a drug is removed from the body.

Definition: The study of the effects of drugs on the body and the mechanisms of their action.
Key Concepts:
- Drug-Receptor Interaction:
  - Drugs exert effects by interacting with specific receptors (e.g., enzymes, hormones).
  - Agonists: activate receptors to produce a response.
  - Antagonists: block receptors, inhibiting a response.
- Dose-Response Relationship:
  - Relationship between the dose of a drug and the magnitude of its effect.
  - Potency: amount of drug needed to produce a specific effect.
  - Efficacy: the maximum effect achievable by the drug.
- Therapeutic Index:
  - Ratio measuring the safety of a drug.
  - Calculated as TD50 (toxic dose for 50% of the population) / ED50 (effective dose for 50% of the population).
- Side Effects and Toxicity:
  - Side effects are unintended effects, which can be mild or severe.
  - Toxicity occurs when drug levels exceed the therapeutic range.

Pharmacokinetics and pharmacodynamics are foundational to understanding how drugs work in the body.
Both fields explore different aspects of drug action and efficacy, which are crucial for safe and effective medication use.

Study of how drugs move throughout the body
Four main processes: absorption, distribution, metabolism, and excretion
Absorption: How drugs enter the bloodstream
- Influenced by route of administration, formulation, and gastrointestinal pH
Distribution: How drugs spread throughout the body
- Influenced by blood flow, drug binding to proteins, and drug solubility
- Drugs are more likely to go to areas with more blood flow (e.g., liver, kidneys, heart)
Metabolism: Chemical changes the body makes to a drug, mainly in the liver
- Helps make drugs more water-soluble, which makes them easier to excrete
Excretion: Removal of drugs from the body, primarily through the kidneys
- Excretion can also happen through bile, sweat, saliva, and milk
- Clearance measures how quickly a drug is removed from the body

Study of how drugs affect the body and how they work
Drug-receptor interaction: Drugs work by binding to specific receptors in the body
- Agonists: Activate receptors to produce a response
- Antagonists: Block receptors, preventing a response
Dose-response relationship: Relationship between the amount of drug and the effect it produces
- Potency: The amount of drug needed to produce a specific effect
- Efficacy: The maximum effect a drug can produce
Therapeutic index: A measure of drug safety
- Calculated by dividing the toxic dose for 50% of the population (TD50) by the effective dose for 50% of the population (ED50)
Side effects and toxicity:
- Side effects are unintended effects of drugs
- Toxicity occurs when drug levels are too high

Pharmacokinetics and pharmacodynamics are important for understanding how drugs work
They help explain how drugs are absorbed, distributed, metabolized, and excreted (pharmacokinetics)
They also explain how drugs interact with the body to produce their effects (pharmacodynamics)

The study of how drugs interact with living systems to produce effects
Drugs exert their actions by binding to specific receptors in the body
Agonists activate receptors and produce biological responses
Antagonists block receptors and prevent biological responses
Dose-response relationship describes the correlation between drug dose and its effect
The threshold dose is the minimum amount of drug required to elicit a measurable effect
Efficacy refers to the maximum effect the drug can produce
Potency denotes the amount of drug needed to achieve a specific effect
Drug actions can involve various mechanisms including enzyme inhibition, modulation of ion channels, and interaction with transporters
Therapeutic index (TI) measures drug safety and is the ratio between toxic dose and effective dose
A higher TI indicates a safer drug with a wider margin between effective and toxic doses
Pharmacogenetics studies how genetic variations influence individual drug responses
Variations in drug metabolism can affect efficacy and toxicity among patients
Factors like age, gender, disease state, and drug interactions can significantly influence pharmacodynamics
Understanding pharmacodynamics is crucial for accurate dose selection, predicting drug interactions, and maximizing therapeutic outcomes