Limited clinical studies have been performed in brain tumor patients evaluating drug delivery to the tumor bed using intracerebral microdialysis measurements [26, 31–34]. To date, the only chemotherapeutic agents evaluated have been methotrexate, temozolomide, bafetinib and 5-flucytosine [26, 32, 33, 35]. Portnow and colleagues studied serum and brain extracellular concentrations of temozolomide via MDC collected at 30 min time intervals post oral drug administration over 24 h. This study evaluated temozolomide drug delivery to the peritumoral non-contrast enhancing area in both primary and metastatic patients (n = 10). Collectively, they found that oral administration of temozolomide yielded an average brain:plasma AUC ratio of 17.8 ± 13.3%, with a peak drug concentration of approximately 2–3 h after administration and undetectable concentrations by 18 h . We designed this study to determine if FDA-approved doses of regadenoson would increase the temozolomide concentration in human brains with malignant glioma as measured by serial brain interstitial fluid assessments.