What is pharmacokinetics in pharmacology?

Definition

Pharmacokinetics is the branch of pharmacology that studies how a drug moves through the body over time. It describes the processes of absorption, distribution, metabolism, and excretion (often abbreviated as ADME). Pharmacokinetics answers the question: "What does the body do to the drug?"

Key parameters include:

• $C_{\text{max}}$: Maximum plasma concentration
• $T_{\text{max}}$: Time to reach $C_{\text{max}}$
• $t_{1/2}$: Elimination half-life
• $V_d$: Volume of distribution
• $CL$: Clearance

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Worked Example

Example:
A patient receives a single 500 mg intravenous (IV) dose of a drug. The plasma concentration decreases according to first-order kinetics with an elimination rate constant $k = 0.2, \text{hr}^{-1}$. What is the plasma concentration after 4 hours if the initial concentration ($C_0$) is $20, text{mg/L}$? **Solution:** First-order elimination is described by: %%MATH_DISPLAY_0%% Plug in the values: - $C_0 = 20, text{mg/L}$ - $k = 0.2, text{hr}^{-1}$ - $t = 4, text{hr}$ Calculate: %%MATH_DISPLAY_1%% Using $e^{-0.8} approx 0.4493$: %%MATH_DISPLAY_2%% --- ## Key Takeaways - Pharmacokinetics describes how the body absorbs, distributes, metabolizes, and excretes drugs (ADME). - Key parameters (e.g., $t_{1/2}$, $V_d$, $CL$) help determine dosing and frequency.

• Understanding pharmacokinetics is essential for safe and effective drug therapy.