Six patients were enrolled on the study from May 2015 to April 2017. Five of the patients were deemed as evaluable. One patient was deemed unevaluable due to microdialysis catheter displacement, which occurred approximately 24 h after insertion. This displacement was attributed to manipulation of the patient’s surgical head dressing post-operatively. This patient was removed from study before any study medications were administered. Table 1 summarizes patient demographics. All patients underwent surgical debulking for their recurrent high grade glioma. Each catheter was placed in peritumoral tissue that was deemed to be non-contrast enhancing tissue by pre-operative MRI. In two patients, catheters were also placed in contrast enhancing areas approximately 5 mm from the surgical bed due to a subtotal resection. Catheter tip locations were accurately determined by superimposed CT and MRI imaging (Fig. 1). All evaluable patients tolerated microdialysis catheter insertion without associated bleeding, infection, pain or other incidents attributable to foreign material placement.Table 1Clinical demographicsPatientAgeGenderDiagnosisCatheter(s) tip placement area149MGlioblastomaNon-contrast and contrast enhancing268MGlioblastomaNon-contrast enhancing332MGlioblastomaNon-contrast and contrast enhancing460MGlioblastomaNon-contrast enhancing551MGlioblastomaNon-contrast enhancing670FGlioblastomaNon-contrast enhancingAll patients diagnosed with recurrent glioblastoma and catheter tips were placed in non-contrast enhancing tumor. In patients 1 and 3, tips were also placed in contrast enhancing tissue Fig. 1Catheter placement imaging. Brain CT and MRI superimposed delineating catheter placement and tumor margins. Patient 1 had one catheter tip placed in non-contrast enhancing area and the second in contrast enhancing tissue (a). Patient 2 had one catheter placed in non-contrast enhancing tissue (b). Superimposed images denote contrast enhancement in green. The white triangle indicates placement of catheter tips