If tissue affinity Kp increases while Q and Vt constant, tissue distribution half-life will:

If tissue affinity Kp increases while Q and Vt constant, tissue distribution half-life will:

• A. Decrease
• B. Increase
• C. Stay the same
• D. Increase because higher tissue affinity slows exit from tissue

Answer: (D)

During distribution, drug moves between plasma and tissue, with the rate governed by how quickly it enters tissue (k12) and how quickly it leaves tissue (k21). Tissue affinity (Kp) tells you how much drug is held in tissue at equilibrium. If Kp increases while blood flow and tissue volume stay the same, more drug is retained in tissue, which means the back-transfer from tissue to plasma slows down (k21 decreases). Since the distribution half-life reflects how fast the system approaches equilibrium between compartments, a slower exit from tissue lengthens this time. Therefore the tissue distribution half-life increases.

During distribution, drug moves between plasma and tissue, with the rate governed by how quickly it enters tissue (k12) and how quickly it leaves tissue (k21). Tissue affinity (Kp) tells you how much drug is held in tissue at equilibrium. If Kp increases while blood flow and tissue volume stay the same, more drug is retained in tissue, which means the back-transfer from tissue to plasma slows down (k21 decreases). Since the distribution half-life reflects how fast the system approaches equilibrium between compartments, a slower exit from tissue lengthens this time. Therefore the tissue distribution half-life increases.