One-Compartment Open Model

One Compartment Open Model explains drug absorption, distribution, and elimination using a single compartment in pharmacokinetics.

One-Compartment Open Model

• The one-compartment open model is one of the simplest pharmacokinetic models used to describe drug disposition in the body.
• It assumes that the body acts as a single, uniform compartment where the drug is evenly distributed instantaneously after administration.

Key Assumptions:

1. The body is represented as a single, homogenous compartment.
2. Drug equilibrates instantly within the compartment after administration.
3. Elimination follows first-order kinetics, meaning that the rate of elimination is proportional to the drug concentration.
4. Drug is removed irreversibly (hence, it is an “open” system).
5. There is no consideration of separate compartments for tissues or organs.

This model is widely used to describe the pharmacokinetics of drugs that distribute rapidly and uniformly in the body after administration.

Mathematical Representation:

• The drug concentration C at time t is given by:
• $C = C_0 e^{-k_e t}$
• Where:
  • $C_0$ = Initial drug concentration
  • ​ $k_e$ = Elimination rate constant
  • t = Time
• This equation shows that the drug concentration decreases exponentially over time.

Types of One-Compartment Models Based on Drug Administration Route

1. The one-compartment model can be adapted for different drug administration routes:
   • Intravenous bolus
   • Intravenous infusion
   • Extravascular administration (e.g., oral, subcutaneous, or intramuscular)

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