A nurse is preparing to administer IV vancomycin to a client. Which laboratory value must be checked BEFORE administration?

VANCOMYCIN is a glycopeptide antibiotic used primarily for MRSA and other gram-positive organisms. It is one of the most important antibiotics to monitor because of significant toxicity risks. NEPHROTOXICITY — RENAL MONITORING: Vancomycin is eliminated by the kidneys; impaired renal function causes accumulation; creatinine and BUN must be checked before initiation and monitored every 2-3 days during therapy; dosing must be adjusted for renal impairment (reduced dose or extended dosing interval based on creatinine clearance); signs of nephrotoxicity: rising creatinine, decreased urine output. OTOTOXICITY — HEARING: Vancomycin can damage hearing (both cochlear and vestibular toxicity); more common with high levels or prolonged therapy; warn clients to report ringing in ears (tinnitus), hearing changes, dizziness. SERUM VANCOMYCIN LEVELS — TROUGH MONITORING: Trough level is drawn just before the next scheduled dose (within 30 minutes); current AUC (area under the curve) monitoring is the preferred approach in many institutions but trough remains common; traditional therapeutic trough: 15-20 mcg/mL for serious infections; levels above 20 mcg/mL significantly increase nephrotoxicity risk. 'RED MAN SYNDROME': Not an allergy but a rate-related reaction — flushing, erythema, and hypotension from too-rapid infusion; prevented by infusing over at least 60 minutes (often 60-90 minutes for 500-1000mg doses); if it occurs, slow or stop infusion, give diphenhydramine. NURSING ROLE: Check renal function labs before each course and monitor during; schedule trough draws correctly; administer slowly; educate client on side effects to report.