Variables
Description
What is this formula?
The one-compartment first-order absorption model describes drug concentration after extravascular administration such as oral, subcutaneous, or intramuscular dosing.
The model assumes:
- a single well-mixed compartment,
- first-order absorption,
- first-order elimination,
- constant pharmacokinetic parameters.
Drug concentration initially rises due to absorption and later decreases as elimination becomes dominant.
When to use it
Use this formula for drugs that can be reasonably represented by a one-compartment model after oral or other extravascular administration.
It is commonly used in pharmacokinetic modeling, formulation development, bioavailability studies, and drug simulations.
Example
A drug is administered orally.
Data:
F = 0.8
Dose = 500 mg
ka = 1.2 h⁻¹
k = 0.2 h⁻¹
Vd = 50 L
t = 4 h
Formula:
C = [F·Dose·ka·(e^(-kt)-e^(-kat))]/[Vd·(ka-k)]
Substitution:
C = [0.8×500×1.2×(e^(-0.2×4)-e^(-1.2×4))]/[50×(1.2-0.2)]
C ≈ 4.18 mg/L
Result:
C ≈ 4.18 mg/L
Applications
- Oral pharmacokinetics
- Drug absorption studies
- Bioavailability assessment
- Pharmacokinetic simulation
- Formulation optimization
Note
This model assumes first-order absorption and first-order elimination. It may not accurately describe drugs exhibiting saturable absorption, nonlinear elimination, delayed absorption, enterohepatic recirculation, or multicompartment distribution. More complex models may be required in such cases.