In a patient with polycythemia, the time to equilibrium for a drug is expected to be:

• A. Longer
• B. No change
• C. Shorter
• D. Impossible to determine

Answer: (C)

The key idea is how quickly a drug moves from blood into tissues and cellular compartments during the distribution phase. In polycythemia, hematocrit is high, so there’s more red blood cell mass and relatively less plasma volume. Drugs that partition into red blood cells or bind within the cellular blood compartment have a larger reservoir to distribute into, and the driving force for transfer into those cells is enhanced. This tends to speed up the redistribution of the drug from plasma into cells and tissues, making the distribution phase complete sooner. As a result, the time to reach equilibrium is shorter. If a drug stayed entirely in plasma, the effect might differ, but for drugs that occupy the cellular blood compartment, polycythemia accelerates distribution.