Final answer:
The most accurate way to assess the effectiveness of an antipyretic in lowering fever is to measure the patient's oral temperature 30 minutes after administration of the medication.
Step-by-step explanation:
To evaluate the effectiveness of an antipyretic medication in reducing fever in a patient with an oral temperature of 101.6° F, the best nursing action is to assess oral temperature 30 minutes after the medication is administered. This approach directly measures the parameter that the antipyretic is intended to influence - body temperature - and provides a quantifiable data point to determine if the medication has produced the desired effect of lowering the fever. Other methods, such as assessing for physical aches touching the forehead to gauge skin temperature or observing skin color for signs of fever-related flushing, are less direct and may not accurately reflect changes in the patient's core temperature.