Once the patient was clinically stable, at least 24 h after the completion of surgery on post-operative day 1, and tolerating oral intake, they were administered temozolomide 150 mg/m2 orally once. On post-operative day 2, each patient was again given temozolomide 150 mg/m2 orally, and approximately 60 min later, each patient was administered intravenous regadenoson 0.4 mg once over 10 s. Previous studies have demonstrated temozolomide peak brain concentrations occur 90–120 min after administration [26, 27]. Additionally, preclinical studies with regadenoson have demonstrated the peak effect on barrier permeability occurs 30–60 min after administration [19, 24, 36]. Thus, we opted to administer regadenoson 60 min after temozolomide to ensure peak concentration of temozolomide in the brain and optimal mechanism of regadenoson action on brain vasculature simultaneously. Regadenoson was given with continuous ECG monitoring for a total of 10 min post injection, in the presence of a staff cardiologist (standard cardiac dosing regimen). Pre-temozolomide blood samples were collected 15 min prior to drug administration and then 1, 2, 3, 4, 8, and 18 h after the dose of temozolomide (5 ml per collection). The samples of blood were collected in heparinized syringes, promptly mixed by inversion, and then placed on wet ice until centrifugation at 1300×g for 10 min at 4 °C (within 1 h). The samples were processed to plasma within 30 min from centrifugation, and the pH of each sample was adjusted to < 4 with the use of 8.5% phosphoric acid. Plasma was then stored frozen at − 70 °C or below until subsequent batch analysis via liquid chromatography-tandem mass spectrometry (LC–MS/MS).