True or False: Increasing drug concentration will enhance therapeutic effect for a perfusion-limited drug but not for a permeability-limited drug.

True or False: Increasing drug concentration will enhance therapeutic effect for a perfusion-limited drug but not for a permeability-limited drug.

• A. False
• B. Partially true
• C. Not enough information
• D. True

Answer: (D)

Distribution can be limited by how fast blood delivers drug to tissues (perfusion) or by how slowly the drug crosses tissue barriers (permeability). In perfusion-limited distribution, tissue uptake is fast relative to blood flow, so increasing plasma concentration raises the amount of drug delivered to and available in the tissue, boosting the therapeutic effect up to other limiting factors. In permeability-limited distribution, the barrier to entry into the tissue is the bottleneck; the rate of transfer into tissue is governed by membrane crossing, so simply increasing plasma levels does not produce the same proportional increase in tissue exposure or effect. Because perfusion-limited drugs respond to higher plasma concentrations with greater tissue exposure, while permeability-limited drugs do not show the same degree of improvement, the statement is true.

Distribution can be limited by how fast blood delivers drug to tissues (perfusion) or by how slowly the drug crosses tissue barriers (permeability). In perfusion-limited distribution, tissue uptake is fast relative to blood flow, so increasing plasma concentration raises the amount of drug delivered to and available in the tissue, boosting the therapeutic effect up to other limiting factors. In permeability-limited distribution, the barrier to entry into the tissue is the bottleneck; the rate of transfer into tissue is governed by membrane crossing, so simply increasing plasma levels does not produce the same proportional increase in tissue exposure or effect. Because perfusion-limited drugs respond to higher plasma concentrations with greater tissue exposure, while permeability-limited drugs do not show the same degree of improvement, the statement is true.