Oral administration of gemcitabine in patients with refractory tumors: a clinical and pharmacologic study.
OBJECTIVE
To determine the toxicity, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of oral gemcitabine (2',2'-difluorodeoxycytidine; dFdC) in patients with cancer.


METHODS
Patients with advanced or metastatic cancer refractory to standard therapy were eligible. Gemcitabine was administered p.o. starting at 1 mg once daily using dose escalation with three patients per dose level. Patients received one of two dosing schemes: (a) once daily dosing for 14 days of a 21-day cycle or (b) every other day dosing for 21 days of a 28-day cycle. Pharmacokinetics were assessed by measuring concentrations of dFdC and 2',2'-difluorodeoxyuridine (dFdU) in plasma and gemcitabine triphosphate in peripheral blood mononuclear cells, and pharmacodynamics by measuring the effect on T-cell proliferation.


RESULTS
Thirty patients entered the study. Oral gemcitabine was generally well-tolerated. The maximum tolerated dose was not reached. Mainly moderate gastrointestinal toxicities occurred except for one patient who died after experiencing grade 4 hepatic failure during cycle two. One patient with a leiomyosarcoma had stable disease during 2 years and 7 months. Systemic exposure to dFdC was low with an estimated bioavailability of 10%. dFdC was highly converted to dFdU, probably via first pass metabolism and dFdU had a long terminal half-life ( approximately 89 h). Concentrations of dFdCTP in peripheral blood mononuclear cells were low, but high levels of gemcitabine triphosphate, the phosphorylated metabolite of dFdU, were detected.


CONCLUSIONS
Systemic exposure to oral gemcitabine was low due to extensive first-pass metabolism to dFdU. Moderate toxicity combined with hints of activity warrant further investigation of the concept of prolonged exposure to gemcitabine.
Veltkamp
Stephan A
SA
Division of Experimental Therapy, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands. s.veltkamp@nki.nl
Jansen
Robert S
RS
Callies
Sophie
S
Pluim
Dick
D
Visseren-Grul
Carla M
CM
Rosing
Hilde
H
Kloeker-Rhoades
Susanne
S
Andre
Valerie A M
VA
Beijnen
Jos H
JH
Slapak
Christopher A
CA
Schellens
Jan H M
JH
D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics*; D019540:Area Under Curve; D049109:Cell Proliferation / Q000187:drug effects; D003841:Deoxycytidine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy*; D013601:T-Lymphocytes / Q000187:drug effects; D000093542:Gemcitabine
D000964:Antimetabolites, Antineoplastic; D003841:Deoxycytidine; D000093542:Gemcitabine