Background and Importance There are currently conflicting results in numerous studies on the effect of neutropenia on vancomycin plasma concentrations.

Aim and Objectives To evaluate the effect of neutropenia on pharmacokinetic parameters in patients treated with vancomycin.

Material and Methods Observational and retrospective study in patients treated with vancomycin in a tertiary level hospital, between July and June 2023. The clinical history was consulted and the following variables were collected: sex, age, creatinine, neutrophil count and vancomycin trough levels in blood. Neutropenic patients were considered if their levels were less than 1.5x10^9 neutrophils/L and vancomycin clearance (CLv) was calculated by the Matzke and Moellering methods. The data were processed in the SPSS v.25 statistical program: the Shapiro Wilks test was performed as a normality test and a statistical test was carried out according to the results (Student’s t-test or Mann-Whitney U-test).

Results We analysed 68 samples in 37 patients; of which 17 were male and a median age of 65 [18–90] years. Patients were classified into two groups according to the number of neutrophils, eight (11%) neutropenic patients and the 60 (89%) non-neutropenic. The Shapiro Wilks normality test showed normality in all variables, however the sample size of one group made it necessary to use a non-parametric test (Mann-Whitney U test). Mean trough levels in neutropenic patients were 9.6 (SD2.96) vs. 11 (SD7.04) in non-neutropenic patients (p=0.991). The mean CLv by Matzke and Moellering methods was 107,83 (SD39) and 88 (SD2.34) respectively in the group of neutropenic patients and in non-neutropenic patients it was 105.13 (SD39.3) and 85 (SD2.21); p=0.228 in both groups.

Conclusion and Relevance Although no statistically significant differences were found, probably due to the sample size, it can be observed that the group of neutropenic patients had lower vancomycin trough levels and a higher clearance than the non-neutropenic group. Furthermore, we can conclude that both methods of calculating Clv are similar in both groups of patients. Further studies are needed to demonstrate the effect of neutropenia on vancomycin levels and its consequences on treatment efficacy.

Conflict of Interest No conflict of interest.