A drug is administered as a constant IV infusion. It has a clearance of 5 L/h and a target steady-state concentration of 2 mg/L. What infusion rate is required to maintain this concentration?

• A 2.5 mg/h
• B 5 mg/h
• C 20 mg/h
• D 10 mg/h ✓

Explanation

At steady state, the rate of drug administration equals the rate of elimination: R₀ = Css × CL. Therefore, R₀ = 2 mg/L × 5 L/h = 10 mg/h. This is the fundamental pharmacokinetic principle that steady-state concentration is determined solely by clearance and infusion rate, not by volume of distribution. Volume of distribution determines only the time to reach steady state (approximately 4–5 half-lives), not the steady-state concentration itself.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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