Steady-State One-Compartment Concentration

What is this formula?

The steady-state one-compartment concentration formula calculates the average drug concentration reached during constant intravenous infusion when the rate of drug input equals the rate of drug elimination.

At steady state, concentration remains approximately constant as long as infusion rate and clearance remain unchanged.

When to use it

Use this formula for a drug administered by constant IV infusion under one-compartment, linear pharmacokinetic assumptions.

It is useful when designing infusion rates or estimating expected steady-state concentration.

Example

A drug is infused at 40 mg/h and its clearance is 5 L/h.

Data:

R0 = 40 mg/h

CL = 5 L/h

Formula:

Css = R0/CL

Substitution:

Css = 40/5

Result:

Css = 8 mg/L

Applications

- Intravenous infusion dosing

- Therapeutic drug monitoring

- Critical care pharmacokinetics

- Maintenance dose design

- Pharmacokinetic simulations

Note

This formula assumes linear pharmacokinetics, constant clearance, and constant infusion rate. It estimates the steady-state concentration after sufficient time has passed, typically about 4 to 5 half-lives. It may not apply accurately to drugs with nonlinear elimination, time-dependent clearance, or multicompartment distribution.