How can obesity influence pharmacokinetic parameters?

• A. Has no effect on PK.
• B. Decreases Vd for lipophilic drugs; increases clearance.
• C. Increases Vd for lipophilic drugs; may affect clearance depending on organ function; dosing often adjusted by weight.
• D. Only affects clearance, not Vd.

Answer: (C)

Obesity adds a lot of adipose tissue that acts as a large reservoir for lipophilic drugs, so the volume of distribution for these drugs increases. With a bigger Vd, a given dose yields a lower peak plasma concentration and often a longer elimination half-life, which can lead to accumulation if dosing isn’t adjusted. Clearance, on the other hand, is more variable and depends on how obesity affects organ function. Hepatic clearance can change with altered hepatic blood flow and enzyme activity, while renal clearance can be influenced by changes in glomerular filtration. Some patients may experience increased clearance due to higher organ perfusion, while others with obesity-related organ dysfunction may have reduced clearance. Because of these complexities, dosing is frequently guided by body weight, using appropriate weight metrics to balance distribution and clearance for lipophilic drugs.