Pharmacokinetic evaluation of gemcitabine and 2′,2′-difluorodeoxycytidine-5′-triphosphate after prolonged infusion in patients affected by different solid tumors

Background: The study determined pharmacokinetic parameters, toxicity profile and preliminary clinical activity of gemcitabine administered i.v. at different infusion rates in patients with a range of solid tumors. Patients and methods: Twenty patients were enrolled for both pharmacokinetic and clinical studies. Gemcitabine 300 mg/m(2) was administered during 1 h, 2 h or 3 h, and as a conventional dose of 1000 mg/m(2) during 30 min infusion. Administration was on days 1, 8 and 15 every 4 weeks. Results: Patients were randomly assigned to one of the four arms. After 30 min infusion of 1000 mg/m(2) gemcitabine the plasma concentration remained above the saturation level of 10-20 mu M, whereas after 1, 2 or 3 h infusion 300 mg/m(2) gemcitabine it remained below the saturation level for most of the time (being in the range 2.5-10 mu M). Gemcitabine triphosphate was determined in the four arms in white blood cells; for infusion times from 0.5 to 3 h there was a progressive enhancement of gemcitabine triphosphate levels. In all evaluable patients the toxicity was mild, myelosuppression being the main toxicity. No grade 3 or 4 toxicities occurred. Clinical response was similar in patients receiving 300 mg/m(2) gemcitabine in 2 and 3 h and in the 1000 mg/m(2) arm. Conclusions: 300 mg/m(2) gemcitabine during 3 h infusion produced the highest accumulation of gemcitabine triphosphate. Thus, to achieve the highest possible gemcitabine triphosphate level, prolonged infusion time would appear to be more important than a high dose administered as a short infusion. However, there was no substantial difference in toxicity or antitumoral activity in the all different patient groups.