Final answer:
The nurse should withhold the drug and notify the prescriber immediately.
Step-by-step explanation:
Based on the information provided, the nurse should take action b. Withhold drug & notify the prescriber immediately. The plasma digoxin level of 0.7 ng/mL is within the therapeutic range for digoxin, which is typically 0.5-2 ng/mL. However, the nurse should still withhold the drug and notify the prescriber to ensure that the dosage is appropriate and to discuss any potential concerns or adjustments.