A phase I and pharmacologic study of weekly gemcitabine in combination with infusional 5-fluorodeoxyuridine and oral calcium leucovorin

Purpose: Since preclinical studies have shown more than additive cytotoxicity and DNA damage with the combination of gemcitabine and 5-fluoro-2′-deoxyuridine (FUDR), we studied this combination in a phase I trial. Methods: Gemcitabine alone was given in cycle 1 as a 24-h, 2-h or 1-h i.v. infusion weekly for 3 of 4 weeks; if tolerated, a 24-h i.v. infusion of FUDR was added with oral leucovorin. The cycle was aborted for grade 3 thrombocytopenia, grade 4 neutropenia, and grade 2 or worse nonhematologic toxicity. Results: During cycle 1, six of eight patients who received 150 or 100 mg/m² over 24 h had dose-limiting neutropenia, thrombocytopenia, fatigue or mucositis. Six of seven patients treated with 1000 mg/m² over 2 h required a gemcitabine dose reduction for cycle 2 (thrombocytopenia, neutropenia, fatigue). Of 25 assessable patients who received gemcitabine 1000 mg/m² over 1 h, 7 did not complete cycle 1 due to thrombocytopenia (n = 6) or diarrhea (n = 1). Of 42 patients entered, 27 received at least one course of gemcitabine/FUDR (5-19.5 mg/m² over 24 h) without appreciable toxicity. Due to a shortage of FUDR, the protocol was closed early. Gemcitabine plasma concentrations averaged 0.061 μM (24 h), 16.3 μM (2 h), and 31.9 μM (1 h). In 21 paired bone marrow mononuclear cell samples obtained before treatment and during FUDR infusion, thymidylate synthase ternary complex was only seen during FUDR infusion. Conclusions: Gemcitabine 100-150 mg/m² over 24 h was poorly tolerated, whereas toxicity was acceptable with 800-1000 mg/m² over 1 h. Inhibition of the target enzyme was demonstrated at all FUDR doses.