Which statement about dialysis clearance is true?

• A. Dialysis can clear a drug only if the drug is unbound
• B. Dialysis clearance increases with higher molecular weight
• C. Dialysis clearance depends on molecular weight, protein binding, Vd, and dialytic parameters
• D. Dialysis always clears all drugs equally

Answer: (C)

Dialysis clearance depends on how readily a drug can move from blood into the dialysate, which is governed by the drug’s properties and the dialysis setup. Lower molecular weight drugs pass through the dialysis membrane more easily, while drugs that are highly protein-bound have only the free portion available for transfer, limiting clearance. Drugs with a large volume of distribution spend much of their time in tissues rather than in the blood, so they are not as accessible to the dialyzer, reducing net clearance. Dialytic parameters—membrane permeability and surface area, dialysate and blood flow rates, and the overall modality—also shape how fast transfer occurs. Put together, these factors mean clearance during dialysis is determined by molecular weight, protein binding, Vd, and dialytic settings, making that statement true.

The other ideas don’t fit because: clearance is not dictated by unbound drug alone—while the free fraction matters, binding dynamics and equilibrium influence how much can be cleared; higher molecular weight generally reduces, not increases, dialysis clearance; and not all drugs are cleared equally—drug properties and dialytic conditions cause wide variation in removal.