How would you expect Vd to change for a drug in a patient with ascites?

How would you expect Vd to change for a drug in a patient with ascites?

• A. Increase in Vd for Hydrophilic Drugs
• B. Decrease in Vd
• C. No Change in Vd
• D. Vd Becomes Irrelevant

Answer: (A)

Ascites expands the extracellular fluid compartment. Hydrophilic drugs, being water-soluble, mostly distribute into this fluid space rather than into fat or cells. When extracellular fluid increases, these drugs have more space to occupy, so the apparent volume of distribution rises. Clinically, this means a given dose yields a lower plasma concentration, and a larger loading dose may be needed to reach the target level. Lipophilic drugs distribute more into tissues and fat, which aren’t greatly expanded by ascites, so their Vd is less affected.

Ascites expands the extracellular fluid compartment. Hydrophilic drugs, being water-soluble, mostly distribute into this fluid space rather than into fat or cells. When extracellular fluid increases, these drugs have more space to occupy, so the apparent volume of distribution rises. Clinically, this means a given dose yields a lower plasma concentration, and a larger loading dose may be needed to reach the target level. Lipophilic drugs distribute more into tissues and fat, which aren’t greatly expanded by ascites, so their Vd is less affected.