In pharmacokinetics, which scenario would most likely increase the rate of distribution to tissues?

In pharmacokinetics, which scenario would most likely increase the rate of distribution to tissues?

• A. Lower capillary permeability
• B. Increased capillary permeability
• C. Decreased blood flow
• D. Lower tissue affinity

Answer: (B)

The rate at which a drug distributes to tissues hinges on how easily it can cross the capillary wall. When capillary permeability is increased, the endothelial barrier becomes more permissive, so more drug molecules can pass from the blood into the interstitial space and then into tissue, speeding up distribution. If permeability is low, crossing the capillary wall is harder and distribution slows. Blood flow to the tissue is another factor: reduced flow means less drug is delivered to the capillaries in the first place, limiting distribution rate. Tissue affinity affects how much drug stays in tissue once it arrives, not how fast it gets there, so lowering affinity doesn’t increase distribution speed and may reduce tissue levels after entry. Inflammation, for example, can raise permeability and thus accelerate distribution to affected tissues.

The rate at which a drug distributes to tissues hinges on how easily it can cross the capillary wall. When capillary permeability is increased, the endothelial barrier becomes more permissive, so more drug molecules can pass from the blood into the interstitial space and then into tissue, speeding up distribution. If permeability is low, crossing the capillary wall is harder and distribution slows. Blood flow to the tissue is another factor: reduced flow means less drug is delivered to the capillaries in the first place, limiting distribution rate. Tissue affinity affects how much drug stays in tissue once it arrives, not how fast it gets there, so lowering affinity doesn’t increase distribution speed and may reduce tissue levels after entry. Inflammation, for example, can raise permeability and thus accelerate distribution to affected tissues.