Variables
Description
What is this formula?
Drug clearance describes the theoretical volume of plasma completely cleared of a drug per unit time. It relates the rate of drug elimination to the drug concentration in plasma.
Clearance is one of the most important pharmacokinetic parameters because it helps determine maintenance dose and dosing interval.
When to use it
Use this formula when the elimination rate of a drug and its plasma concentration are known.
It is commonly applied in pharmacokinetic analysis, renal clearance studies, hepatic clearance estimation, and therapeutic drug monitoring.
Example
A drug is eliminated at a rate of 50 mg/h, and its plasma concentration is 5 mg/L.
Data:
Re = 50 mg/h
C = 5 mg/L
Formula:
CL = Re/C
Substitution:
CL = 50/5
Result:
CL = 10 L/h
Applications
- Maintenance dose calculation
- Therapeutic drug monitoring
- Renal and hepatic pharmacokinetic analysis
- Drug development studies
- Comparison of elimination capacity between patients
Note
This formula is a simplified pharmacokinetic relationship. Clearance may vary with concentration, organ function, protein binding, blood flow, and nonlinear kinetics. It is most directly applicable when drug elimination behaves approximately linearly over the concentration range considered.