A hospitalized patient is receiving a drug by continuous intravenous infusion at 5 mg/h and has reached steady state with a plasma concentration of 2 mg/L. The infusion rate is increased to 10 mg/h. Which statement about the new steady state is correct?

• A The new steady state concentration will be 4 mg/L and will be reached sooner than before
• B The new steady state concentration cannot be predicted without knowing the volume of distribution
• C The new steady state concentration will be 2 mg/L because clearance increases with dose
• D The new steady state concentration will be 4 mg/L and the time to reach it depends only on the half-life ✓

Explanation

For a drug with first-order elimination given by constant infusion, Css equals infusion rate divided by clearance, so doubling the rate doubles Css to 4 mg/L. The time required to reach any new steady state is determined solely by the half-life, roughly four to five half-lives regardless of dose or route. Clearance does not rise with dose in linear kinetics, and volume of distribution influences the loading dose and half-life, not the eventual plateau.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.