One-Compartment Model with Intravenous Infusion

One Compartment Model with Intravenous Infusion explains constant drug input, steady state, and elimination in pharmacokinetics.

Definition of One-Compartment Model with Intravenous Infusion:

• Intravenous (IV) infusion is the continuous administration of a drug into the bloodstream at a controlled rate over a prolonged period.

Process:

1. The drug is infused at a constant rate (R) into the bloodstream.
2. Unlike IV bolus, the drug concentration gradually increases until it reaches a steady-state concentration.
3. The drug is simultaneously being distributed and eliminated.

Pharmacokinetics of IV Infusion:

• The concentration of the drug in plasma at time t is given by:
• $C = \frac{R}{k_e V_d} \left( 1 – e^{-k_e t} \right)$
• Where:
  • R = Infusion rate (mg/hr)
  •  $k_e$ = Elimination rate constant
  • ​$V_d$ = Volume of distribution

Steady-State Concentration (:

• After a certain period, the drug reaches a steady-state concentration, where the rate of drug administration equals the rate of elimination.
• $C_{ss} = \frac{R}{k_e V_d}$
• At steady-state, the drug concentration remains constant as long as the infusion continues.

Key Advantages of IV Infusion:

• Controlled plasma drug levels (avoids peak and trough fluctuations).
• Useful for drugs with a narrow therapeutic index (e.g., heparin, morphine).
• Can be stopped immediately if adverse effects occur.

Limitations:

• Slower onset of action compared to IV bolus.
• Requires careful monitoring to maintain desired drug levels.
• Risk of infection at the injection site if administered for a long period.

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