A drug with a high volume of distribution is more likely to be which type of molecule?

A drug with a high volume of distribution is more likely to be which type of molecule?

• A. Hydrophilic
• B. Lipophilic
• C. Ionized
• D. Polar

Answer: (B)

A high volume of distribution means the drug moves beyond the plasma and into tissues. Lipophilic drugs partition into lipid-rich tissues and cross cell membranes readily, so they accumulate in tissues rather than staying in the blood. This extensive tissue distribution drives a large Vd. In contrast, hydrophilic, polar, or ionized molecules don’t cross membranes as easily and remain mainly in plasma or extracellular fluid, leading to a smaller Vd. So lipophilicity best explains a high Vd.

A high volume of distribution means the drug moves beyond the plasma and into tissues. Lipophilic drugs partition into lipid-rich tissues and cross cell membranes readily, so they accumulate in tissues rather than staying in the blood. This extensive tissue distribution drives a large Vd. In contrast, hydrophilic, polar, or ionized molecules don’t cross membranes as easily and remain mainly in plasma or extracellular fluid, leading to a smaller Vd. So lipophilicity best explains a high Vd.