Final answer:
The nurse should monitor the client's vital signs before and after administering epoetin, as it is essential for assessing response to the medication and detecting adverse effects.
Step-by-step explanation:
When administering epoetin intravenously to a client who has renal failure, the correct action for the nurse to take is B. Monitor the client's vital signs before and after administration. Monitoring vital signs is crucial because it helps in assessing the client's response to the medication and in detecting any adverse effects such as hypertension. It is crucial to continuously assess a patient's hemoglobin levels during epoetin therapy to avoid an excessive increase, which can be dangerous. Known allergies should never be disregarded, as even rare allergic reactions can be severe.