Phase I Trial of Temozolomide Using an Extended Continuous Oral Schedule

Abstract

Temozolomide, a methylating imidazotetrazinone, has antitumor activity against gliomas, malignant melanoma, and mycosis fungoides and is presently administered as a 5-day oral schedule every 4 weeks. This Phase I study aimed to determine the maximum tolerated dose of temozolomide administered as a single oral daily dose for a continuous 6- or 7-week period, evaluate the plasma pharmacokinetics on this schedule, and compare total plasma exposure over 7 weeks with the conventional 5-day regimen. Twenty-four patients with varying tumor types (17 of 24 gliomas) received temozolomide. All had clinically evaluable, refractory disease; normal renal, hepatic, and bone marrow function; and WHO performance status ≤2. Temozolomide was administered at 50 mg/m²/day, increasing by 25 mg/m²/day/cohort until at 100 mg/m²/day grade 4 myelotoxicity forced dose reductions to 85 mg/m²/day, then 75 mg/m²/day. At 75 mg/m²/day the regimen was extended to 7 weeks, allowing the future potential combination with irradiation for primary gliomas. Patient responses (standard Union International Contre Cancer criteria; for gliomas objective response) and toxicity were assessed. Temozolomide plasma pharmacokinetics were determined on day 1 and at the beginning of the final week of administration (n = 5). The most frequent toxicities were myelosuppression and grades 1 and 2 nausea and vomiting. Grade 4 leucopenia and thrombocytopenia occurred in one of four patients receiving 100 mg/m²/day temozolomide and in one of seven patients receiving 85 mg/m²/day. These hematological toxicities did not exceed grade 2 in 10 patients receiving 75 mg/m²/day temozolomide. One of 4 malignant melanoma patients and 7 of 17 glioma patients (41%) demonstrated tumor responses. The overall response rate for this prolonged schedule was 33% (objective response, 7 of 24 patients; partial response, 1 of 24 patients); also, 6 of 17 glioma patients maintained SD. Peak plasma temozolomide concentrations were obtained 30–90 min after oral administration. Elimination in plasma was best described by a monoexponential equation with an elimination half-life of 96 ± 16 min. No plasma accumulation of temozolomide occurred. Toxicity was greatest in higher dose cohorts, with a resultant maximum tolerated dose of 85 mg/m²/day, whereas lower dose cohorts tolerated the schedule well. The area under the temozolomide plasma versus time curve was noncumulative between the first and last week of the schedule. Temozolomide administration of 75 mg/m²/day over a 7-week period permits a 2.1-fold greater drug exposure/4 weeks in comparison with the 5-day schedule of 200 mg/m²/day repeated every 28 days. The overall response rate was 33% (glioma patients, 41% and a further 25% SD). Temozolomide (75 mg/m²/day) for 7 weeks is the recommended starting dose for further assessment of this schedule.