Background Temozolomide is an alkylating agent approved by the U.S. Food and Drug Administration in 1999 for the treatment of patients with primary brain tumors. The aim of this study was to confirm the bioequivalence and safety of two strengths (20-100 mg) of generic temozolomide in the form of TOZ039 and Temodal(R)capsules administered to brain tumor patients. Study design An open-label, randomized, two-phase, two-period, crossover pharmacokinetic study was performed in a single institution. The reference and test drugs were prescribed at a dose of 150 mg/m(2)daily from days 1 to 5 of a 28-day cycle in the first phase; in the second phase, either a 150- or 200-mg/m(2)dose was prescribed, depending on patient tolerance. On days 1 and 2 of each phase, a fixed 200-mg dose was administered either as ten 20-mg capsules in the first cycle or two 100-mg capsules in the second cycle. Drug administration in the first two days was randomized, i.e., if TOZ309 was administered on day 1, Temodal(R)was administered on day 2, and vice versa. The rest of the prescribed dose was administered in the form of Temodal(R)and spread equally over days 3-5. Blood samples were obtained for pharmacokinetic evaluation on days 1 and 2. Bioequivalence was demonstrated if the geometric means ratio of the three main pharmacokinetic parameters (mean maximum plasma concentration (C-max), area under the concentration-time curve (AUC) 0-t, AUC(0-infinity)) fell within the equivalence boundary of 80-125%. Results Twenty-nine glioblastoma multiforme or anaplastic astrocytoma patients were enrolled and dosed with the test and reference formulations under fasting conditions. The 90% confidence interval of the geometric means ratio for C-max(91.08%, 106.18%), AUC(0-t)(98.62%,102.18%), and AUC(0-infinity)(98.65%, 102.21%) was well within the 80%-125% range for the 20-mg capsule, as was the C-max(90.49%, 113.32%), AUC(0-t)(99.89%, 104.63%) and AUC(0-infinity)(99.99%, 104.67%) for the 100-mg capsule drug product. Additionally, all the secondary pharmacokinetic parameters were not significantly different. After two cycles of treatment, there was no mortality among the 29 patients, treatment-related severe adverse events, or events that would require study discontinuation; however, one significant adverse effect (life-threatening seizures) occurred and was related to disease progression. Adverse events were reported in 82.8% (24/29) patients, and treatment emergent adverse events were reported in 72.4% (21/29) patients. Conclusion It can be concluded that 20-mg and 100-mg capsules of TOZ309 are bioequivalent to Temodal(R)capsules of the same strength under fasting conditions.