Final answer:
Rhogam is used to prevent HDN in an Rh-negative mother with an Rh-positive fetus by inactivating fetal Rh-positive erythrocytes in the maternal blood. A standard dose is given, and the exact amount of fetal blood neutralized by a specific dosage of Rhogam is based on clinical guidelines.
Step-by-step explanation:
The question pertains to the use of Rhogam, a drug administered to Rh-negative women during pregnancy to prevent hemolytic disease of the newborn (HDN) which can occur in subsequent pregnancies if the baby is Rh-positive. Rhogam contains anti-Rh antibodies that inactivate any fetal Rh-positive erythrocytes (red blood cells) that enter the maternal circulation, thereby preventing the mother's immune system from becoming sensitized and producing its own Rh antibodies which could attack the Rh-positive red blood cells of a future fetus. However, the original question which asks about the specific amount of fetal blood that can be neutralized by 300 micrograms of Rhogam cannot be directly answered without additional clinical information. Typically, a standard dose of Rhogam is given, which is considered effective for the vast majority of cases. The precise amount of fetal blood that can be neutralized by this dosage is established by clinical guidelines but is not specified in the information provided.