In this pilot feasibility study, we utilized MDC to determine the neuropharmacokinetics of temozolomide co-administered with regadenoson to assess temozolomide drug entry. We hypothesized that regadenoson would transiently impact the permeability of temozolomide as it did in rodents resulting in increased brain interstitium (BI) and brain:plasma AUC ratio. The primary aim of this trial was to measure brain interstitial temozolomide concentrations pre and post regadenoson using MDC in patients with recurrent high grade glioma. The secondary endpoint was to evaluate tolerability of temozolomide with a single dose of regadenoson in the post-operative setting.