Prolonged infusion gemcitabine: A clinical phase I study at low- (300 mg/m2) and high-dose (875 mg/m2) levels

Gemcitabine (GEM) is a novel nucleoside analogue with a unique mechanism of action. Preliminary studies have shown a mild, schedule-dependent toxic profile with a broad range of MTDs and promising antitumor activity in various solid tumors. This phase I study describes the infusion length-effect relationships of low- (300 mg/m²) and high-dose (875 mg/m²) GEM, administered on days 1, 8 and 15 at 4-week intervals in a step-wise escalation of duration (≤ 33%) at a starting level of 60 minutes. At least 3 patients entered each infusion-level step and 3 more cases were treated in the presence of significant toxicity. Conservative criteria for toxicity were employed, including treatment delay until recovery with infusion de-escalation in the subsequent course. Forty-seven patients (29 at low- and 18 at high-dose GEM levels) with various solid tumors, including 9 (taken as a reference) who had received the same dose levels over 30 min. entered the study. All but 9 patients (with pancreatic cancer) had been previously treated with chemotherapy and all had extensive visceral disease. A striking infusional-effect relationship was observed at both GEM dose levels. Four escalation steps were required to define the maximum tolerated infusion time (MTIT) at 6 hours for 300 mg/m² GEM, with leucopenia being dose-limiting. At 875 mg/m², although no limiting toxicity was observed (in spite of increased severity of leucopenia), no escalation was attempted following the 1-hour infusion, due to the limiting rate (58% of 12 patients) of toxic delay requiring shorter infusions. Toxicity was usually mild (no grade 4 event was recorded) showing the usual profile, although there was a trend towards increased non-hematologic toxicity (i.e. LFT abnormalities) as compared with the MTD previously defined using a 30-min. infusion schedule (1370 mg/m²). Eight patients achieved a PR: 1 with NSCLC, 1 with gastric and 2 with bladder cancer at 300 mg/m² (1 with a 3- and 3 with a 6-hour infusion) and 2 with pancreatic, 1 with cervical and another with bladder cancer at 875 mg/m² (all but one with a 1-hour infusion). These data clearly suggest that the infusion duration is an important independent factor that influences the clinical effects of GEM. The present study not only defined the toxic profiles and the MTITs of the selected dose levels but demonstrated that GEM retained the antitumor activity at doses as small as 300 mg/m² when given as a prolonged infusion. Further studies should clarify the underlying mechanism(s) responsible for the erratic dose-effect relationships of GEM and establish the optimal dose-infusion level in the treatment of solid tumors.