Question

In one-compartment model, after IV bolus administration, the plasma concentration declines

• A. Sigmoidally with time
• B. Exponentially with time
• C. Logarithmically with time
• D. Linearly with time

Hint:

In a one-compartment model, the body is treated as a single uniform space. When a drug is given as an IV bolus (the whole dose injected at once into the blood), it spreads instantly and then starts to be eliminated.

Answer 1

The Correct Option is B

Step 1: IV bolus in a one-compartment model.
When a drug is given as an intravenous bolus, it is instantly distributed throughout the body (one compartment). There is no absorption phase; elimination begins immediately.

Step 2: First-order kinetics equation.
In a one-compartment model with first-order elimination: \( C(t) = C_0 \cdot e^{-k_e t} \) where C₀ is initial concentration, k_e is the elimination rate constant, and t is time. This is an exponential decay equation.

Step 3: What exponential decline means.
Exponential decline means the same fraction of drug is eliminated per unit time. On a linear plot, this appears as a curved downward slope. On a semi-logarithmic plot (log C vs time), it appears as a straight line.

Step 4: Eliminate the distractors.
Sigmoidal decline suggests an S-shaped curve (not first-order). Logarithmic decline is not the same as exponential. Linear decline would imply zero-order kinetics, where a constant amount (not fraction) is removed per unit time.

Step 5: Conclusion.
After IV bolus, plasma concentration in a one-compartment model declines exponentially with time, following first-order kinetics.


Answer: Option (2) — Exponentially with time