Background and importance According to the study by Bury D et al,1 vancomycin dosage should be 25% higher than standard dosages in neutropenic patients due to increased clearance of vancomycin in this population. Renal hyperfiltration is considered a possible mechanism.
Aim and objectives We aimed to determine the prevalence of subtherapeutic drug exposure in neutropenic patients under therapeutic drug monitoring (TDM) and the subsequent TDM dosage adjustments.
Material and methods This was a retrospective and descriptive study from 2010 to 2019. Patients with haematological disease with neutropenia and receiving vancomycin TDM by pharmacists were included. Demographic variables, Cockcroft–Gault creatinine clearance (CrCl), initial dosage, dose adjustments and the first two trough levels were collected. Renal impairment was defined as CrCl <60 mL/min. Dosages of 15–20 mg/kg/dose and trough levels between 10 and 20 µg/mL were considered optimal for intermittent infusion schedules, according to international guidelines.2
Results Forty-one patients were included (58.5% men). Median age was 62.9 years (IQR 19.4–48) and 80% of patients had CrCl ≥60 mL/min. We found that 65.9% of patients did not achieve therapeutic levels in the first determination; most (77.8%) received a subtherapeutic initial dose. Also, 22.2% achieved a subtherapeutic level despite being treated with a correct initial vancomycin dose, requiring ≥25% increase in the total vancomycin dose.
Regarding TDM dosage adjustments, 63.4% of patients required an increase in the total daily dose (77% needed a shorter dosing interval while 23% needed higher doses with the same dosing interval).
Conclusion and relevance More than a half of the patients had subtherapeutic vancomycin levels. Initial underdosage was the main cause of subtherapeutic levels. Nevertheless, 22.2% required ≥25% increase in dose to achieve target drug concentrations despite an initial therapeutic regimen, according to previous evidence. Shortening the dosing interval was the main TDM dosage adjustment, probably due to increased vancomycin clearance in this population.
References and/or acknowledgements 1. Bury D, et al. The effect of neutropenia on the clinical pharmacokinetics of vancomycin in adults. Eur J Clin Pharmacol 2019;75:921–928.
2. Rybak M, Lomaestro B, Rotschafer JC, et al. Therapeutic monitoring of vancomycin in adult patients: a consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm 2009;66:82–98.
No conflict of interest.
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