What is Pharmacokinetics?

Pharmacokinetics is the branch of pharmacology that describes what the body does to a drug over time. It focuses on how a drug is absorbed, distributed, metabolized, and eliminated, commonly summarized as ADME.

• How a drug enters the bloodstream
• Influenced by route of administration (oral, intravenous (IV), intramuscular (IM), etc.), drug formulation, and patient factors
• Determines bioavailability (fraction of drug that reaches systemic circulation)

• How the drug spreads throughout body tissues and fluids
• Affected by blood flow, tissue binding, plasma protein binding, and lipid solubility
• Described by volume of distribution (Vd)

• Chemical modification of the drug, mainly in the liver
• Often involves cytochrome P450 enzymes
• Can activate prodrugs or inactivate active drugs

• Removal of the drug from the body
• Primarily via kidneys (urine), but also bile, feces, lungs, and sweat
• Determines clearance and half-life

• Half-life (t½): Time for plasma drug concentration to reduce by half
• Clearance (Cl): Volume of plasma cleared of drug per unit time
• Steady state: Point where drug intake equals elimination
• Bioavailability (F): Fraction of administered dose reaching circulation

In short, pharmacokinetics explains drug concentration changes over time, helping determine dosing, frequency, and route of administration.