From the Guidelines
Trough levels of medications should be checked just before the next scheduled dose, when the concentration of the drug in the bloodstream is at its lowest point, as recommended by the Infectious Diseases Society of America 1. This timing is crucial for medications with narrow therapeutic windows such as vancomycin, aminoglycosides (gentamicin, tobramycin, amikacin), anticonvulsants (phenytoin, carbamazepine, valproic acid), immunosuppressants (tacrolimus, cyclosporine, sirolimus), and lithium. For example, if a patient takes vancomycin every 12 hours, the trough level should be drawn approximately 30 minutes before the next scheduled dose. It's essential to document the exact time of the last dose and when the sample was collected to ensure accurate interpretation, as stated in the vancomycin therapeutic guidelines 1. Consistently timing blood draws is vital because trough levels help determine if the medication concentration remains above the minimum effective concentration without falling too low, which could lead to treatment failure or antimicrobial resistance. Some key points to consider when monitoring trough levels include:
- Trough vancomycin concentrations are the most accurate and practical method to guide vancomycin dosing 1
- Serum trough concentrations should be obtained at steady-state conditions, prior to the fourth or fifth dose 1
- Monitoring of peak vancomycin concentrations is not recommended 1
- Target trough levels typically range from 10-20 mcg/mL depending on the infection being treated, with higher targets for more serious infections like endocarditis or meningitis 1
- Trough vancomycin monitoring is recommended for serious infections and patients who are morbidly obese, have renal dysfunction, or have fluctuating volumes of distribution 1
From the FDA Drug Label
Close monitoring of serum concentrations of vancomycin may be warranted in these patients. Close monitoring of serum concentrations of vancomycin is recommended in these patients. Measurement of vancomycin serum concentrations can be helpful in optimizing therapy, especially in seriously ill patients with changing renal function.
The trough level of vancomycin should be checked in patients where close monitoring is warranted, such as:
- Pediatric patients
- Neonates
- Patients with impaired renal function
- Elderly patients
- Seriously ill patients with changing renal function 2
From the Research
Trough Level Monitoring
- Trough levels are used to monitor the concentration of certain medications in the blood, particularly those with a narrow therapeutic index (NTI) 3, 4.
- The timing of trough level monitoring depends on the medication and the individual patient's characteristics, such as renal function and age 5, 6.
Vancomycin Trough Levels
- Vancomycin trough levels are typically monitored to ensure that the concentration of the medication is within a therapeutic range, usually between 15-20 mg/L 5, 6, 7.
- However, studies have shown that trough levels may not always be a reliable indicator of the medication's effectiveness or toxicity, and that area under the curve (AUC) guided monitoring may be a more accurate approach 5, 6.
- The American Society of Health-System Pharmacists guidelines recommend AUC-guided monitoring for vancomycin, and studies have shown that this approach can reduce the risk of nephrotoxicity 6.
Factors Affecting Trough Levels
- Renal function is a significant factor in determining trough levels, as medications are often cleared from the body through the kidneys 5, 6.
- Age, comorbid illnesses, and concomitant medications can also affect trough levels and should be taken into account when monitoring medication concentrations 3, 4, 7.
Clinical Outcomes and Costs
- Studies have shown that targeting higher vancomycin trough levels can improve clinical outcomes, such as reducing the duration of therapy and improving success rates 7.
- However, higher trough levels can also increase the risk of nephrotoxicity, which can lead to longer hospital stays and increased costs 6, 7.