During pregnancy, which combination of changes can alter Vd and fu?

• A. Increased plasma volume, reduced albumin, and altered tissue perfusion
• B. Decreased plasma volume, increased albumin, and reduced tissue perfusion
• C. No change in plasma volume or protein binding
• D. Decreased tissue perfusion with increased protein binding

Answer: (A)

During pregnancy, several physiologic changes shift how drugs distribute in the body and how much is bound to plasma proteins. The rise in plasma volume expands the intravascular and extracellular spaces, increasing the apparent volume of distribution (Vd), especially for hydrophilic drugs that distribute mainly into body fluids. At the same time, albumin levels fall due to hemodilution, reducing protein binding and increasing the fraction unbound (fu) for drugs that normally bind to albumin. Changes in tissue perfusion, with greater blood flow to many tissues and to the placenta, further influence how quickly and extent distribution occurs into tissues, also contributing to a larger Vd. Taken together, the combination of increased plasma volume, decreased albumin, and altered tissue perfusion best explains why both Vd can rise and fu can change during pregnancy. The other options describe changes that do not reflect the common pregnancy physiology and would not account for the observed shifts in distribution and protein binding.