What is the reported range of enzyme inhibition/ transporter occupancy at doses of 300-900 mg?

• A. 10-20%
• B. 38-68%
• C. 70-90%
• D. 80-100%

Answer: (B)

Enzyme inhibition or transporter occupancy describes how much of the target is bound by the drug at a given dose. For a dose range of 300–900 mg, the occupancy is reported to be about 38–68%, meaning roughly one-third to two-thirds of the target sites are inhibited. This partial inhibition reflects how plasma concentrations reached at these doses interact with the drug’s binding affinity, yielding a substantial but not complete block of the enzyme or transporter. Individual differences in absorption, metabolism, protein binding, and tissue distribution explain the variability and the spread of the range. Occupancy tends to rise with concentration but plateaus as binding sites saturate, so even higher doses within this range don’t typically achieve near-total inhibition in most people. Therefore, 38–68% is the best fit for what’s observed at 300–900 mg.