Which statement best describes the role of lipophilicity in obesity-related drug distribution?

• A. Lipophilicity is the primary driver of how obesity distorts drug distribution
• B. TBW-based dosing is the best universal approach
• C. Hydrophilicity is the primary driver
• D. Dosing is unaffected by obesity

Answer: (A)

In obesity, how a drug distributes in the body is driven mainly by lipophilicity because the expanded fat mass provides a much larger reservoir for lipophilic compounds. Lipophilic drugs readily partition into adipose tissue, so as fat stores increase, the volume of distribution for these drugs increases. That means the same dose can lead to lower blood concentrations and potentially longer persistence in the body, which is a common reason dosing for obese patients must be reconsidered. Hydrophilic drugs, which stay more in water-filled compartments, don’t experience the same degree of change since those compartments don’t expand to the same extent as fat, so their distribution is less altered by obesity. TBW-based dosing is not universally best because it doesn’t account for the large fat mass that mainly affects lipophilic drugs, and saying dosing is unaffected by obesity ignores the real shifts in distribution and exposure.