Steady-State Concentration Calculator

About this calculator

For a drug given as a continuous intravenous infusion, the plasma concentration rises and then levels off once the rate of drug entering the body equals the rate the body clears it — this plateau is the steady-state concentration (Css), and it depends only on the infusion rate and the drug’s clearance: Css = Infusion rate (R0) / Clearance (CL).

This relationship is basic pharmacokinetics, and it’s why Css is reached (practically) after about four to five drug half-lives regardless of the infusion rate — only the level it settles at changes with rate, not how long it takes to get there. Clinicians and pharmacists use this formula when dosing continuous infusions such as vasopressors, sedatives, or aminoglycoside antibiotics, to predict the concentration a given infusion rate will produce, or to work backward and pick an infusion rate that targets a desired concentration. This calculator computes Css from the infusion rate and clearance you enter — it is not medical advice and does not replace clinical dosing judgment.