A constant IV infusion of eflornithine at 1000 mg/h resulted in a steady state plasma concentration of 600 mg/L. What infusion rate would be required to obtain a steady state plasma concentration of 500 mg/L?[Fill in the blank]

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BlackTom AI · Accepted Answer

To approach this, recognize that at steady state for a constant IV infusion, the plasma concentration is proportional to the infusion rate, assuming clearance remains constant.

Option a: 500 mg/h. If we reduce the rate to 500 mg/h from 1000 mg/h, the steady-state concentration would roughly halve from 600 mg/L to about 300 mg/L, not 500 mg/L. Thus this option underestimates the required rate.

Option b: 1667 mg/h. Increasing the rate to 1667 mg/h would, by proportionality, raise the steady-state concentration to roughly 1000 mg/L (since 1667/1000 ≈ 1.667, and 1.667 × 600 mg/L ≈ 1000 mg/L). This overshoots the target 500 mg/L, so this option is too high.

Option c: 833 mg/h. Using direct proportionality, rate_needed = (desired concentration / current concentration) × current rate = (500 / 600) × 1000 = (5/6) × 1000 ≈ 833 mg/h. This matches the target 500 mg/L when clearance is unchanged, so this option aligns with the pharmacokinetic relationship.

Option d: 1200 mg/h. This increases the rate by 20% relative to 1000 mg/h, which would scale the concentration up by about 20%, giving around 720 mg/L, higher than the desired 500 mg/L. Therefore this option is too high.

Option e: 600 mg/h. This is a modest 40% reduction from 1000 mg/h, which would yield a steady-state concentration around 360 mg/L (assuming linear scaling with rate), not 500 mg/L. Hence this option does not meet the target.

In summary, the correct rate is the one that scales linearly with the desired concentration relative to the known condition: 500 mg/L is five-sixths of 600 mg/L, so the infusion rate should be five-sixths of 1000 mg/h, which is about 833 mg/h. The other options either under- or over-shoot the target due to incorrect scaling or misapplication of the proportional relationship.

A constant IV infusion of eflornithine at 1000 mg/h resulted in a steady state plasma concentration of 600 mg/L. What infusion rate would be required to obtain a steady state plasma concentration of 500 mg/L?[Fill in the blank]

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