Recently, it was reported that when vancomycin levels are determined after port sampling, levels can be falsely increased potentially leading to wrong dose adjustments.

The investigators conducted an in vitro experiment using several central venous port devices, in which different flushing techniques were evaluated yielding residual vancomycin levels of less than 0.5 mg/L.

In this study, the investigators want to evaluate this flushing technique in vivo in 15 patients admitted with catheter-related infection and treated with systemic vancomycin and vancomycin antibiotic lock.

The purpose is to assess if correct flushing can avoid spurious vancomycin levels obtained via port sampling.

Inclusion Criteria:

• adult patients,
• having central venous port device,
• treated with systemic vancomycin in combination with vancomycin antibiotic lock

Exclusion Criteria:

• pregnant women,
• children,
• patients with 'do not resuscitate' (DNR) code

Adult patients admitted for catheter related infection with methicillin-resistant coagulase-negative staphylococci (MR-CNS) and treated with systemic vancomycin in combination with vancomycin antibiotic lock via central venous port device.