Final answer:
The nurse should advise the client to notify the healthcare provider immediately if a rash occurs after taking ampicillin sodium, as this could indicate a serious allergic reaction or a severe condition requiring urgent medical attention.
Step-by-step explanation:
If a client is receiving ampicillin sodium (Omnipen) for a sinus infection, the nurse should instruct the client to notify the healthcare provider immediately if a rash occurs. While nausea, diarrhea, and headache can be common side effects of antibiotics, a rash may indicate an allergic reaction, which can be serious. Additionally, an antibiotic-associated rash could be a sign of a more severe condition such as Stevens-Johnson syndrome or toxic epidermal necrolysis, both of which require urgent medical attention. Prompt reporting of a rash is essential for timely evaluation and appropriate management of potentially serious adverse reactions.