Pharmacokinetics: Movement of Drugs in the Body

Pharmacokinetics

Definition: The study of the movement of drugs within the body, including absorption, distribution, metabolism, and excretion.

Key Concepts:

• Absorption:
  • The process by which a drug enters the bloodstream
  • Factors affecting absorption: route of administration, dosage form, pH, and blood flow
• Distribution:
  • The process by which a drug is dispersed throughout the body
  • Factors affecting distribution: blood flow, protein binding, and lipid solubility
• Metabolism:
  • The process by which a drug is chemically altered by the body
  • Types of metabolism: phase I (oxidation, reduction, hydrolysis) and phase II (conjugation)
  • Major organs involved in metabolism: liver, kidneys, and intestines
• Excretion:
  • The process by which a drug is eliminated from the body
  • Major routes of excretion: kidneys (urine), liver (bile), and lungs (exhaled air)

Pharmacokinetic Parameters:

• Bioavailability (F): The percentage of the administered dose that reaches the systemic circulation
• Volume of Distribution (Vd): The apparent volume of fluid that contains the drug at the same concentration as the plasma
• Clearance (CL): The rate at which a drug is eliminated from the body
• Half-Life (t1/2): The time it takes for the plasma concentration of a drug to decrease by 50%

Pharmacokinetic Models:

• One-Compartment Model: A simple model that assumes the drug is distributed uniformly throughout the body
• Two-Compartment Model: A more complex model that assumes the drug is distributed between two compartments: central and peripheral

Clinical Applications:

• Dose Adjustment: Pharmacokinetic parameters are used to adjust the dose of a drug based on individual patient factors, such as age, weight, and renal function
• Therapeutic Drug Monitoring: Pharmacokinetic parameters are used to monitor the plasma concentration of a drug and adjust the dose accordingly

Pharmacokinetics

• Study of the movement of drugs within the body, including absorption, distribution, metabolism, and excretion

Absorption

• Process by which a drug enters the bloodstream
• Factors affecting absorption:
  • Route of administration
  • Dosage form
  • pH
  • Blood flow

Distribution

• Process by which a drug is dispersed throughout the body
• Factors affecting distribution:
  • Blood flow
  • Protein binding
  • Lipid solubility

Metabolism

• Process by which a drug is chemically altered by the body
• Types of metabolism:
  • Phase I (oxidation, reduction, hydrolysis)
  • Phase II (conjugation)
• Major organs involved in metabolism:
  • Liver
  • Kidneys
  • Intestines

Excretion

• Process by which a drug is eliminated from the body
• Major routes of excretion:
  • Kidneys (urine)
  • Liver (bile)
  • Lungs (exhaled air)

Pharmacokinetic Parameters

• Bioavailability (F): Percentage of the administered dose that reaches the systemic circulation
• Volume of Distribution (Vd): Apparent volume of fluid that contains the drug at the same concentration as the plasma
• Clearance (CL): Rate at which a drug is eliminated from the body
• Half-Life (t1/2): Time it takes for the plasma concentration of a drug to decrease by 50%

Pharmacokinetic Models

• One-Compartment Model: Simple model that assumes the drug is distributed uniformly throughout the body
• Two-Compartment Model: More complex model that assumes the drug is distributed between two compartments: central and peripheral

Clinical Applications

• Dose Adjustment: Pharmacokinetic parameters are used to adjust the dose of a drug based on individual patient factors, such as age, weight, and renal function
• Therapeutic Drug Monitoring: Pharmacokinetic parameters are used to monitor the plasma concentration of a drug and adjust the dose accordingly