Foundational Concepts in Pharmacokinetics

Foundational Concepts in Pharmacokinetics

• Pharmacokinetics (PK) is the study of how a drug moves through the body over time.
• Pharmacodynamics (PD) is the study of how a drug affects the body.
• Key processes involved in PK are absorption, distribution, metabolism, and excretion (ADME)
• PK principles are applied in clinical settings for safe and effective drug management.

Learning Objectives

• Define pharmacokinetics and pharmacodynamics
• Define absorption, distribution, metabolism, and excretion
• Define pharmacokinetic parameters: volume of distribution, half-life (t_1/2), clearance, etc.

Basic Concepts for Drug Action

• Pharmacokinetics (PK):
  • Pharmaco: Drug
  • Kinetics: Motion (drug movement in the body)
  • Processes include absorption, distribution, metabolism, and excretion (ADME)
• Pharmacodynamics (PD):
  • Pharmaco: Drug
  • Dynamics: Action (power/effect of a drug in the body)
  • Includes drug-receptor interactions, potency, and efficacy

Drug Administration

• Pharmacokinetic phase: Dose, dosage form, frequency, and route of administration impact drug levels over time.
• Pharmacodynamic phase: Drug concentration at the site of action determines the effect of the drug. The effect can be therapeutic or toxic.

What is Pharmacokinetics?

• Pharmacokinetics: Study of drug absorption, distribution, metabolism, and excretion (ADME).
• Clinical pharmacokinetics: Applying PK principles to achieve safe and effective drug therapy for individual patients.

Absorption

• Absorption is the entry of a drug into the systemic circulation.
• Important considerations for drug absorption include the route of administration.

Distribution

• Distribution is the partitioning of a drug throughout different body locations.
• Drugs distribute between plasma, extracellular fluid, and intracellular compartments.

Metabolism

• Metabolism is the process where a drug is chemically modified.
• Commonly involves specialized enzymatic systems, and is crucial for drug clearance.
• Key locations include liver (often a major site) and gut.

Drug Elimination

• The liver and kidneys are the major organs responsible for drug elimination.
• Metabolism and excretion occur in the liver, excretion in the kidneys.
• Excretion routes include urine and bile (major), sweat and breast milk (minor).

Therapeutic Concentration Range

• Therapeutic Concentration Range (TCR) is the plasma concentration range of a drug that is safe and effective for treating a disease.
• Ranges from a minimum effective concentration (MEC) to a maximum tolerated concentration (MTC).
• AUC (area under the curve) represents the total drug exposure over a given time.

Pharmacokinetic Parameters

• Volume of Distribution (Vd): A proportionality constant relating the amount of drug in the body to its concentration in a biological fluid (like plasma). Vd is measured in liters and represents the apparent volume in which the drug is distributed.
• Clearance (Cl): The volume of plasma cleared of a drug over a specified time period. Calculated as the rate of elimination divided by the plasma concentration.
• Half-life (t_1/2): The time required for the plasma concentration of a drug to decrease by one-half.

First- and Zero-Order Elimination

• Zero-order elimination: Drug elimination rate is constant, regardless of drug concentration.
• First-order elimination: Drug elimination rate is proportional to drug concentration.

Body Fluids and Tissues

• Body fluids include plasma, interstitial fluid, and intracellular fluid, with percentages of total body weight varying between the different body fluid compartments.

Whole Blood, Plasma & Serum

• Plasma and serum represent the part of whole blood after removing formed elements/cells and fibrinogen.
• Plasma is preferred for PK studies because the formed elements aren't included and their influences eliminated.

Therapeutic Drug Monitoring

• Monitoring drug concentrations to tailor doses based on individual patient needs.
• Aims at maintaining drug levels within the desired therapeutic range.
• A crucial part of this process involves understanding and applying pharmacokinetics (PK) and pharmacodynamics (PD).

Relationship between PD & PK

• Prescribed Dosing Regimen and patient compliance affect the PK phase of drug action. Adverse events or medication errors can also influence PK.
• The resulting drug effects/ action is directly related to drug receptors' status, genetic factors, drug-drug interactions, and tolerance.

Math Principles

• Logarithms (Logs): Used to simplify complex calculations.
• Exponents: used in mathematical calculations to express repeated multiplication.
• Natural log number: 2.71828

Graphing Data

• Linear graphs and semi-log graphs are used to display drug concentration over time, assisting in determining how drugs are metabolized.

This quiz covers the foundational concepts of pharmacokinetics and pharmacodynamics. You will explore key processes like absorption, distribution, metabolism, and excretion (ADME), as well as pharmacokinetic parameters such as volume of distribution and half-life. Enhance your understanding of how drugs move through and affect the body.