Variables
Description
What is this formula?
The Average Steady-State Concentration (Css,av) estimates the mean plasma concentration maintained during repeated dosing once steady state has been reached.
When to use it
Use this formula when designing maintenance regimens, evaluating therapeutic exposure, and comparing dosing schedules.
Example
Data:
F = 0.8
D = 500 mg
Cl = 5 L/h
tau = 12 h
Formula:
Css,av = (F × D)/(Cl × tau)
Substitution:
Css,av = (0.8 × 500)/(5 × 12)
Result:
Css,av = 6.67 mg/L
Applications
- Therapeutic drug monitoring
- Maintenance dose design
- Pharmacokinetic modeling
- Bioavailability studies
- Clinical pharmacology
Note
This formula assumes linear pharmacokinetics, steady-state conditions, and constant drug clearance. Variations in absorption, metabolism, organ function, and patient adherence may cause actual average concentrations to differ from the calculated value.