Edema or fluid overload affects distribution of hydrophilic drugs by:

Edema or fluid overload affects distribution of hydrophilic drugs by:

• A. Reducing extracellular volume and decreasing distribution
• B. Not affecting distribution in the body
• C. Decreasing Vd and shortening half-life
• D. Expanding extracellular volume and increasing Vd

Answer: (D)

Edema expands extracellular fluid, which is the space where hydrophilic drugs mainly distribute. When this space gets larger, the volume of distribution increases for these drugs. With a fixed dose, more drug spreads into the expanded extracellular compartment, lowering peak plasma concentrations and often prolonging how long the drug stays in the body; if clearance remains the same, the half-life increases because it depends on the ratio of Vd to clearance. The other statements don’t fit because reducing extracellular volume would shrink distribution, claiming no effect ignores the change in extracellular fluid, and stating that Vd decreases with a shorter half-life contradicts the relationships between Vd and half-life.

Edema expands extracellular fluid, which is the space where hydrophilic drugs mainly distribute. When this space gets larger, the volume of distribution increases for these drugs. With a fixed dose, more drug spreads into the expanded extracellular compartment, lowering peak plasma concentrations and often prolonging how long the drug stays in the body; if clearance remains the same, the half-life increases because it depends on the ratio of Vd to clearance. The other statements don’t fit because reducing extracellular volume would shrink distribution, claiming no effect ignores the change in extracellular fluid, and stating that Vd decreases with a shorter half-life contradicts the relationships between Vd and half-life.