Vancomycin Trough Timing

Draw the vancomycin trough level immediately before the fourth or fifth dose to ensure steady-state concentrations have been achieved. 1, 2

Timing Rationale

Steady-state is reached just before the fourth dose, making this the earliest reliable time point for accurate therapeutic drug monitoring 2
The trough must be drawn within 30 minutes before the next scheduled dose administration 3
Drawing levels earlier than the fourth dose (before steady-state) produces unreliable results that cannot guide dosing decisions 4

For serious infections (bacteremia, endocarditis, osteomyelitis, meningitis, hospital-acquired pneumonia, severe skin/soft tissue infections): target 15-20 mg/L 1, 2, 4
For less severe infections: target 10-15 mg/L 2
These ranges achieve an AUC/MIC ratio ≥400 for organisms with MIC ≤1 mg/L 1, 4

Morbidly obese patients require trough monitoring regardless of infection severity 2, 4
Patients with renal dysfunction or on dialysis need frequent monitoring, at least twice weekly even during continuous renal replacement therapy 4
Patients with fluctuating volumes of distribution (critically ill, septic shock, burns) have unpredictable pharmacokinetics requiring close monitoring 3
Treatment duration >7 days mandates ongoing trough monitoring 1, 2

Recheck trough with each dose adjustment to confirm the new regimen achieves target levels 4
For stable patients on prolonged therapy: recheck trough weekly 4
For patients with deteriorating or improving renal function: more frequent monitoring is mandatory 4
Monitor serum creatinine at least twice weekly throughout therapy to detect nephrotoxicity early 4

Short-course therapy ≤5 days does not require trough monitoring before the fourth dose 4
Lower-intensity dosing targeting troughs ≤15 mg/L for less severe infections may not require monitoring before the fourth dose 4

If trough >20 mg/L: immediately hold the next scheduled dose and recheck trough before administering any subsequent doses 1, 2, 4
Once trough decreases to 15-20 mg/L: resume vancomycin at reduced dose (approximately 15-20% reduction) or extend dosing interval 1
If trough <15 mg/L for serious infections: increase dose or shorten dosing interval and recheck before next dose 1

Never draw trough levels before the fourth dose unless using continuous infusion, as pre-steady-state levels are unreliable 2, 4
Never monitor peak levels—this provides no clinical value and is not recommended 1, 2, 4
Never continue the same dose when trough exceeds 20 mg/L, as this dramatically increases nephrotoxicity risk 4
Never use vancomycin when MIC ≥2 mg/L—switch to alternative antibiotics as target AUC/MIC ratios are not achievable 1, 4

For continuous infusion vancomycin: measure steady-state concentration after a loading dose, not a traditional trough 3
Target steady-state concentration is approximately 20 mg/L for continuous infusion, which can be higher for specific sites (CNS, endocarditis, bone) 3