Fludarabine phosphate is rapidly dephosphorylated to 2-fluoro-ara-A and then phosphorylated intracellularly by deoxycytidine kinase to the active triphosphate, 2-fluoro-ara-ATP. This metabolite appears to act by inhibiting DNA polymerase alpha, ribonucleotide reductase and DNA primase, thus inhibiting DNA synthesis. The mechanism of action of this antimetabolite is not completely characterized and may be multi-faceted.
Phase I studies in humans have demonstrated that fludarabine phosphate is rapidly
converted to the active metabolite, 2-fluoro-ara-A, within minutes after intravenous
infusion. Consequently, clinical pharmacology studies have focused on 2-fluoro-ara-A
pharmacokinetics. After the five daily doses of 25 mg 2-fluoro-ara-AMP/m2
to cancer patients infused over 30 minutes, 2-fluoro-ara-A concentrations show
a moderate accumulation. During a 5-day treatment schedule, 2-fluoro-ara-A plasma
trough levels increased by a factor of about 2. The terminal half-life of 2-fluoro-ara-A
was estimated as approximately 20 hours. In vitro, plasma protein binding
of fludarabine ranged between 19% and 29%.
A correlation was noted between the degree of absolute granulocyte count nadir and increased area under the concentration x time curve (AUC).
Limited pharmacokinetic data for FLUDARA FOR INJECTION are available from a
published study of children (ages 1-21 years) with refractory acute leukemias
or solid tumors (Children's Cancer Group Study 0971). When FLUDARA
FOR INJECTION was administered as a loading dose over 10 minutes immediately
followed by a 5-day continuous infusion, steady-state conditions were reached
Patients with Renal Impairment
The total body clearance of the principal metabolite 2-fluoro-ara-A correlated
with the creatinine clearance, indicating the importance of the renal excretion
pathway for the elimination of the drug. Renal clearance represents approximately
40% of the total body clearance. Patients with moderate renal impairment (17
- 41 mL/min/m2) receiving 20% reduced Fludara dose had a similar
exposure (AUC; 21 versus 20 nM • h/mL) compared to patients with normal
renal function receiving the recommended dose. The mean total body clearance
was 172 mL/min for normal and 124 mL/min for patients with moderately impaired
Two single-arm open-label studies of FLUDARA FOR INJECTION have been conducted
in adult patients with CLL refractory to at least one prior standard alkylating-agent
containing regimen. In a study conducted by M.D. Anderson Cancer Center (MDAH),
48 patients were treated with a dose of 22-40 mg/m2 daily for 5 days
every 28 days. Another study conducted by the Southwest Oncology Group (SWOG)
involved 31 patients treated with a dose of 15-25 mg/m2 daily for
5 days every 28 days. The overall objective response rates were 48% and 32%
in the MDAH and SWOG studies, respectively. The complete response rate in both
studies was 13%; the partial response rate was 35% in the MDAH study and 19%
in the SWOG study. These response rates were obtained using standardized response
criteria developed by the National Cancer Institute CLL Working Group3
and were achieved in heavily pre-treated patients. The ability of FLUDARA FOR
INJECTION to induce a significant rate of response in refractory patients suggests
minimal cross-resistance with commonly used anti-CLL agents.
The median time to response in the MDAH and SWOG studies was 7 weeks (range of 1 to 68 weeks) and 21 weeks (range of 1 to 53 weeks) respectively. The median duration of disease control was 91 weeks (MDAH) and 65 weeks (SWOG). The median survival of all refractory CLL patients treated with FLUDARA FOR INJECTION was 43 weeks and 52 weeks in the MDAH and SWOG studies, respectively.
Rai stage improved to Stage II or better in 7 of 12 MDAH responders (58%) and
in 5 of 7 SWOG responders (71%) who were Stage III or IV at baseline. In the
combined studies, mean hemoglobin concentration improved from 9.0 g/dL at baseline
to 11.8 g/dL at the time of response in a subgroup of anemic patients. Similarly,
average platelet count improved from 63,500/mm3 to 103,300/mm3
at the time of response in a subgroup of patients who were thrombocytopenic
1. Preventing Occupational Exposures to Antineoplastic and Other Hazardous
Drugs in Health Care Settings. NIOSH Alert 2004-165.
3. American Society of Health-System Pharmacists. ASHP guidelines on handling
hazardous drugs. Am J Health-Syst Pharm. 2006: 63 1172-1193.