Final answer:
The primary rationale for administering pain medication in this manner is to achieve better pain control than with one medication alone.
Step-by-step explanation:
The primary rationale for administering pain medication in this manner, a combination of an opioid analgesic and a nonsteroidal anti-inflammatory drug (NSAID), is to achieve better pain control than with one medication alone. Opioids are effective in relieving pain, but they can have side effects and risks such as respiratory depression, addiction, and overdose. By combining the opioid with an NSAID, the patient can benefit from the pain-relieving properties of both medications while minimizing the potential adverse effects of the opioid.