From the Guidelines
The first trough level for vancomycin should be drawn just before the fourth dose, which would be approximately 24 hours after starting therapy if administering 500mg every 6 hours. This recommendation is based on the guidelines provided by the Infectious Diseases Society of America, as outlined in the study by 1, which suggests that trough vancomycin concentrations should be obtained at steady state conditions, prior to the fourth or fifth dose. The study by 1 also supports this timing, stating that all patients receiving prolonged courses of vancomycin treatment should have at least 1 steady-state trough serum concentration measured just before the fourth dose. Some key points to consider when drawing the first trough level include:
- Collecting the blood sample within 30 minutes before the fourth dose is administered
- Ensuring that the medication has reached steady state concentrations in the body, which typically takes 3-4 half-lives
- Documenting the exact time the sample was collected and when the previous dose was administered to ensure accurate interpretation of results
- Targeting trough concentrations of 10-15 mg/L for most infections, and 15-20 mg/L for more serious infections like endocarditis, osteomyelitis, or MRSA pneumonia, as suggested by 1.
From the FDA Drug Label
The usual daily intravenous dose is 2 g divided either as 500 mg every 6 hours or 1 g every 12 hours. Each dose should be administered at no more than 10 mg/min or over a period of at least 60 minutes, whichever is longer.
The first trough for vancomycin, if started today with a dose of 500mg Q6hrs, would be immediately before the second dose, which is 6 hours after the first dose 2.
From the Research
Vancomycin Trough Levels
- The first trough for vancomycin is typically measured before the fourth dose, assuming a dosing interval of every 6 hours (Q6hrs) 3, 4.
- For a patient started on 500mg Q6hrs, the first trough level would be measured approximately 12-18 hours after the first dose, just before the fourth dose is administered.
- Factors that can affect vancomycin trough levels include age, gender, renal function, and weight 3, 5.
- Therapeutic vancomycin trough levels are generally considered to be between 15-20 mg/L for severe infections and 10-15 mg/L for less severe infections 3, 6.
Timing of Trough Measurement
- The timing of trough measurement is crucial to ensure accurate assessment of vancomycin levels 4, 7.
- Trough levels should be measured at steady state, which is typically achieved after 3-5 doses of vancomycin 4.
- Measuring trough levels too early or too late can lead to inaccurate results and potentially affect treatment outcomes 5, 6.
Clinical Implications
- Achieving therapeutic vancomycin trough levels is important for effective treatment of gram-positive infections 3, 6.
- High vancomycin trough levels (≥ 15 mg/L) have been associated with increased risk of nephrotoxicity, but also with improved clinical outcomes in some studies 5, 6.
- Further research is needed to fully understand the relationship between vancomycin trough levels and clinical outcomes 4, 7.