Phase I study of paclitaxel administered by ten-day continuous infusion

Pre-clinical data have suggested that prolonged exposure to paclitaxel enhances its cytotoxicity, but various clinical trials utilizing long-term infusions of paclitaxel have been limited by unacceptable hematologic toxicity, most notably significant neutropenia. A phase I study of paclitaxel administered over 10 days, was performed to evaluate the hematologic and non-hematologic toxicities as well as to determine the maximum-tolerated dose for the 10-day infusion duration.

Twenty-nine solid tumor patients (predominantly non-small cell lung cancer and head and neck cancer) were treated with paclitaxel at doses ranging from 5 mg/m2/day to 25 mg/m2/day administered as a 10-day continuous infusion via a pump every 21 days. Dose escalation was permitted within individual patients. Dose-limiting toxicity (DLT) was defined as grade 3 or 4 non-hematologic toxicity, ANC < or = 500 or platelet count < or = 25,000 for > or = 7 days or febrile neutropenia. The maximum tolerated dose (MTD) was defined as the highest dose level at which less than two out of six patients developed DLT. All of the patients had received prior chemotherapy; approximately two-thirds had received prior radiation as well. All patients received standard pre-medications for paclitaxel, including anti-histamines and corticosteroids. Prophylactic granulocyte colony-stimulating factor (G-CSF) was not used.

A total of 110 courses of paclitaxel were administered to 29 patients. The incidence of hematologic and non-hematologic toxicity was quite low among the patients treated at dose levels below 17 mg/m2/day. At higher doses, non-hematologic toxicities including arthralgias, myalgias, fatigue, nausea, stomatitis, and peripheral neuropathy were seen, although nearly all of the toxicities were less than grade 3 (NCI toxicity criteria). Hematologic toxicity mostly consisted of neutropenia and was more common at dose levels of 17 mg/m2/day or higher. Nevertheless, even at the highest dose levels (21 mg/m2/day and 25 mg/m2/day) grade 3 or 4 neutropenia occurred in only 50% of patients. Dose-limiting hematologic toxicity occurred in 2 of 4 patients treated at the 25 mg/m2/day dose level.

Paclitaxel can be safely administered as a 10-day infusion. The MTD for this schedule is 210 mg/m2. Unlike the 96-hour paclitaxel infusions, dose-reduction for myelosuppression may not be necessary because the MTD of paclitaxel when administered over a 10-day infusion is similar to the MTD of paclitaxel when infused over 3 or 24 hours.