PHARMACOKINETICS AND DRUG
DISPOSITION
A pharmacokinetic-based test to prevent
severe 5-fluorouracil toxicity
Background and Objectives: Dihydropyrimidine dehydrogenase (DPD) plays a key role in the catabolism of
5-fluorouracil (5-FU) to 5-fluoro-5,6-dihydrouracil (5-FDHU), and as such, an impairment of DPD has
been recognized as an important factor for altered 5-FU and 5-FDHU pharmacokinetics, predisposing
patients to the development of severe 5-FU–associated toxicity. Our objectives were to avoid severe 5-FU
toxicities in patients with greatly impaired 5-FU and 5-FDHU pharmacokinetics after the administration of
a reduced test dose of 5-FU and to investigate possible 5-FU or 5-FDHU pharmacokinetic parameters of the
test dose related to the most common drug toxicities that affect patients after the first cycle of 5-FU
chemotherapy.
Methods: Pharmacokinetics of 5-FU/5-FDHU and DPD activity in peripheral blood mononuclear cells
(PBMCs) were examined in 188 gastrointestinal cancer patients given a test dose of 5-FU, 250 mg/m
2
,2
weeks before starting the planned 5-FU treatment of 370 mg/m
2
plus L-folinic acid, 100 mg/m
2
, for 5 days
every 4 weeks. Drug levels were examined by HPLC, and toxicities were graded according to World Health
Organization criteria.
Results: The 5-FU test dose was well tolerated in all patients. Of 188 patients, 3 (1.6%) had marked
alterations of 5-FU/5-FDHU pharmacokinetics (ie, 5-FU half-life [t
½
] >5 hours, 5-FU total body clear-
ance [CL
TB
] <1L·h
1
·m
2
, and 5-FDHU time to reach maximum plasma concentration [t
max
] >45
minutes); they were excluded from 5-FU treatments and treated with irinotecan, which was well tolerated.
The plasma disposition of 5-FU in the remaining 185 patients revealed an area under the curve (AUC) of 3.73
2.18 h · g/mL (mean SD), maximum plasma concentration (C
max
) of 16.78 8.61 g/mL, and t
½
of 0.16 0.15 hour, whereas the CL
TB
was 65.67 31.86 L · h
1
·m
2
. The 5-FDHU plasma profile
showed a C
max
value of 3.64 1.94 g/mL, whereas the t
max
value was 26.63 10.06 minutes, with an
AUC value of 3.71 1.90 h· g/mL. The PBMC DPD activity was 202.15 141.14 pmol
5-FDHU · min
1
· mg
1
protein (95% confidence interval, 165-239.3 pmol 5-FDHU · min
1
· mg
1
pro-
tein). A significant correlation between 5-FU AUC and 5-FDHU AUC was found (r 0.5492, P < .0001),
continued on next page
Guido Bocci, MD, PhD, Cecilia Barbara, MD, Francesca Vannozzi, MD,
Antonello Di Paolo, MD, PhD, Alessandro Melosi, MD, Gemma Barsanti, MD,
Giacomo Allegrini, MD, Alfredo Falcone, MD, Mario Del Tacca, MD, PharmD, and
Romano Danesi, MD, PhD Pisa, Lucca, and Livorno, Italy
From the Division of Pharmacology and Chemotherapy, Department
of Internal Medicine, University of Pisa, Pisa; Division of Medical
Oncology, General Hospital, Lucca; and Division of Medical On-
cology, General Hospital, Livorno.
Supported by a research grant from CNR-MIUR (National Research
Council–Ministry of Education, University and Research) (legge
449/97-99) and from the Ministry of Education, University and
Research to Dr Del Tacca (PRIN, Programmi di Ricerca di
Interesse Nazionale, project 2004) and Dr Danesi (PRIN project
2005).
Received for publication June 12, 2006; accepted June 19, 2006.
Reprint requests: Guido Bocci, MD, PhD, Division of Pharmacology
and Chemotherapy, Department of Internal Medicine, University
of Pisa, Via Roma, 55, I-56126 Pisa, Italy.
E-mail: g.bocci@med.unipi.it
Clin Pharmacol Ther 2006;80:384-95.
0009-9236/$32.00
Copyright © 2006 by the American Society for Clinical Pharmacology
and Therapeutics.
doi:10.1016/j.clpt.2006.06.007
384