**Core Concept**
Erythropoietin (EPO) is a glycoprotein hormone that stimulates red blood cell production in the bone marrow. Longer-acting EPO derivatives are used to treat anemia in patients with chronic kidney disease, cancer, and HIV/AIDS.

**Why the Correct Answer is Right**
Darbepoetin alfa is a longer-acting EPO derivative that has an increased half-life due to additional carbohydrate molecules. This allows for less frequent dosing compared to native EPO. Darbepoetin alfa binds to the EPO receptor, activating the JAK/STAT signaling pathway, which promotes the transcription of genes involved in erythropoiesis. This results in increased production of red blood cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Sargramostim is a granulocyte-macrophage colony-stimulating factor (GM-CSF) analog, not an EPO derivative. It is used to stimulate white blood cell production in patients with cancer and HIV/AIDS.
**Option C:** Dornase alfa is a recombinant deoxyribonuclease (DNase) enzyme that breaks down DNA in the airways, reducing sputum viscosity in patients with cystic fibrosis. It is not related to EPO or erythropoiesis.
**Option D:** Oprelvekin is a recombinant interleukin-11 (IL-11) analog that stimulates platelet production in patients with thrombocytopenia. It is not an EPO derivative.

**Clinical Pearl / High-Yield Fact**
When selecting an EPO derivative, consider the patient's anemia severity, renal function, and response to previous treatments. Longer-acting EPO derivatives like darbepoetin alfa may be preferred for patients who require less frequent dosing.

**✓ Correct Answer: B. Darbepoetin alfa**