A client is receiving IV vancomycin. The infusion has been running for 20 minutes and the nurse notices facial flushing and hypotension. What is the likely cause and nursing action?

RED MAN SYNDROME (vancomycin-related): MECHANISM: NOT an allergic reaction — it is a direct mast cell degranulation triggered by too-rapid infusion; the faster the infusion, the more histamine release; PRESENTATION: Facial flushing/erythema; neck and chest redness ('red man' distribution); hypotension; pruritus (itching); can progress to bronchospasm and hypotension if severe; TIMING: Typically occurs during infusion or within 30-60 minutes of starting; TREATMENT: STOP or SLOW the infusion immediately; diphenhydramine (Benadryl) IV or IM; once reaction resolves, restart at a SLOWER rate; the standard recommendation is to infuse vancomycin at NO FASTER than 10-15 mg/min (typically 1g over at least 60 minutes, preferably 90 minutes); DISTINGUISH FROM TRUE ALLERGY: True allergy to vancomycin exists but is much less common; anaphylaxis would show urticaria, angioedema, bronchospasm — treat with epinephrine; the distribution and timing pattern distinguishes Red Man Syndrome from true allergy.