CLINICAL PHARMACOLOGY
Mechanism Of Action
Colony-stimulating factors are glycoproteins which act on
hematopoietic cells by binding to specific cell surface receptors and
stimulating proliferationâ differentiation commitmentâ and some end-cell
functional activation.
Endogenous G-CSF is a lineage-specific colony-stimulating
factor that is produced by monocytesâ fibroblasts, and endothelial cells. G-CSF
regulates the production of neutrophils within the bone marrow and affects
neutrophil progenitor proliferationâ differentiation, and selected end-cell
functions (including enhanced phagocytic abilityâ priming of the cellular
metabolism associated with respiratory burstâ antibody-dependent killing, and
the increased expression of some cell surface antigens). G-CSF is not
species-specific and has been shown to have minimal direct in vivo or in vitro
effects on the production or activity of hematopoietic cell types other than
the neutrophil lineage.
Pharmacodynamics
In phase 1 studies involving 96 patients with various
nonmyeloid malignanciesâ NEUPOGEN administration resulted in a dose-dependent
increase in circulating neutrophil counts over the dose range of 1 to 70
mcg/kg/day. This increase in neutrophil counts was observed whether NEUPOGEN
was administered intravenous (1 to 70 mcg/kg twice daily), subcutaneous (1 to
3 mcg/kg once daily), or by continuous subcutaneous infusion (3 to 11
mcg/kg/day). With discontinuation of NEUPOGEN therapyâ neutrophil counts
returned to baseline in most cases within 4 days. Isolated neutrophils
displayed normal phagocytic (measured by zymosan-stimulated chemoluminescence)
and chemotactic (measured by migration under agarose using
N-formyl-methionyl-leucyl-phenylalanine [fMLP] as the chemotaxin) activity in
vitro.
The absolute monocyte count was reported to increase in a
dose-dependent manner in most patients receiving NEUPOGEN; howeverâ the
percentage of monocytes in the differential count remained within the normal
range. Absolute counts of both eosinophils and basophils did not change and
were within the normal range following administration of NEUPOGEN. Increases in
lymphocyte counts following NEUPOGEN administration have been reported in some
normal subjects and patients with cancer.
White blood cell (WBC) differentials obtained during
clinical trials have demonstrated a shift towards earlier granulocyte
progenitor cells (left shift)â including the appearance of promyelocytes and
myeloblastsâ usually during neutrophil recovery following the
chemotherapy-induced nadir. In additionâ Dohle bodiesâ increased granulocyte granulationâ
and hypersegmented neutrophils have been observed. Such changes were transient
and were not associated with clinical sequelae, nor were they necessarily
associated with infection.
Pharmacokinetics
Filgrastim exhibits nonlinear pharmacokinetics. Clearance
is dependent on filgrastim concentration and neutrophil count: G-CSF
receptor-mediated clearance is saturated by high concentration of NEUPOGEN and
is diminished by neutropenia. In addition, filgrastim is cleared by the kidney.
Subcutaneous administration of 3.45 mcg/kg and 11.5
mcg/kg of filgrastim resulted in maximum serum concentrations of 4 and 49
ng/mLâ respectivelyâ within 2 to 8 hours. After intravenous administration, the
volume of distribution averaged 150 mL/kg and the elimination half-life was
approximately 3.5 hours in both normal subjects and cancer subjects. Clearance
rates of filgrastim were approximately 0.5 to 0.7 mL/minute/kg. Single
parenteral doses or daily intravenous dosesâ over a 14-day periodâ resulted in comparable
half-lives. The half-lives were similar for intravenous administration (231
minutesâ following doses of 34.5 mcg/kg) and for subcutaneous administration
(210 minutesâ following NEUPOGEN dosages of 3.45 mcg/kg). Continuous 24-hour
intravenous infusions of 20 mcg/kg over an 11 to 20-day period produced
steady-state serum concentrations of filgrastim with no evidence of drug
accumulation over the time period investigated. The absolute bioavailability of
filgrastim after subcutaneous administration is 60% to 70%.
Specific Populations
Patients Acutely Exposed To Myelosuppressive Doses Of Radiation
The pharmacokinetics of filgrastim is not available in
patients acutely exposed to myelosuppressive doses of radiation. Based on
limited pharmacokinetics data in irradiated non-human primates, the area under
the time-concentration curve (AUC), reflecting the exposure to filgrastim in
non-human primates at 10 mcg/kg dose of NEUPOGEN, appears to be similar to that
in humans at 5 mcg/kg. Simulations conducted using the population
pharmacokinetic model indicates that the exposures to filgrastim at a NEUPOGEN
dose of 10 mcg/kg in patients acutely exposed to myelosuppressive doses of
radiation are expected to exceed the exposures at a dose of 10 mcg/kg in
irradiated non-human primates.
Pediatric Patients
The pharmacokinetics of filgrastim in pediatric patients
after chemotherapy are similar to those in adult patients receiving the same
weight-normalized doses, suggesting no age-related differences in the
pharmacokinetics of filgrastim [see Use In Specific Populations].
Renal Impairment
In a study with healthy volunteers, subjects with
moderate renal impairment, and subjects with end-stage renal disease (n = 4 per
group), higher serum concentrations were observed in subjects with end-stage
renal disease. However, dose adjustment in patients with renal impairment is
not necessary.
Hepatic Impairment
Pharmacokinetics and pharmacodynamics of filgrastim are
similar between subjects with hepatic impairment and healthy subjects (n =
12/group). The study included 10 subjects with mild hepatic impairment
(Child-Pugh Class A) and 2 subjects with moderate hepatic impairment
(Child-Pugh Class B). Therefore, filgrastim dose adjustment for patients with hepatic
impairment is not necessary.
Animal Toxicology And Pharmacology
Filgrastim was administered to monkeysâ dogsâ hamstersâ
ratsâ and mice as part of a nonclinical toxicology program, which included
studies up to 1-year duration.
In the repeated-dose studiesâ changes observed were
attributable to the expected pharmacological actions of filgrastim (i.e.â
dose-dependent increases in white blood cell countsâ increased circulating
segmented neutrophilsâ and increased myeloid:erythroid ratio in bone marrow).
Histopathologic examination of the liver and spleen revealed evidence of
ongoing extramedullary granulopoiesis, and dose-related increases in spleen
weight were seen in all species. These changes all reversed after
discontinuation of treatment.
Clinical Studies
Patients With Cancer Receiving Myelosuppressive
Chemotherapy
The safety and efficacy of NEUPOGEN to decrease the
incidence of infectionâ as manifested by febrile neutropeniaâ in patients with
nonmyeloid malignancies receiving myelosuppressive anti-cancer drugs were
established in a randomizedâ double-blindâ placebo-controlled trial conducted
in patients with small cell lung cancer (Study 1).
In Study 1, patients received up to 6 cycles of
intravenous chemotherapy including intravenous cyclophosphamide and doxorubicin
on day 1; and etoposide on days 1, 2, and 3 of 21 day cycles. Patients were
randomized to receive NEUPOGEN (n = 99) at a dose of 230 mcg/m² (4 to 8
mcg/kg/day) or placebo (n = 111). Study drug was administered subcutaneously
daily beginning on day 4, for a maximum of 14 days. A total of 210 patients
were evaluable for efficacy and 207 were evaluable for safety. The demographic
and disease characteristics were balanced between arms with a median age of 62
(range 31 to 80) years; 64% males; 89% Caucasian; 72% extensive disease and 28%
limited disease.
The main efficacy endpoint was the incidence of febrile
neutropenia. Febrile neutropenia was defined as an ANC < 1,000/mm³ and
temperature > 38.2°C. Treatment with NEUPOGEN resulted in a clinically and
statistically significant reduction in the incidence of infectionâ as
manifested by febrile neutropenia, 40% for NEUPOGEN-treated patients and 76%
for placebo-treated patients (p < 0.001). There were also statistically
significant reductions in the incidence and overall duration of infection
manifested by febrile neutropenia; the incidence, severity and duration of
severe neutropenia (ANC < 500/mm³); the incidence and overall duration of
hospital admissions; and the number of reported days of antibiotic use.
Patients With Acute Myeloid Leukemia Receiving Induction Or
Consolidation Chemotherapy
The safety and efficacy of NEUPOGEN to reduce the time to
neutrophil recovery and the duration of fever, following induction or
consolidation chemotherapy treatment of patients with acute myeloid leukemia
(AML) was established in a randomized, double-blindâ placebo-controlledâ
multi-center trial in patients with newly diagnosed, de novo AML (Study 4).
In Study 4 the initial induction therapy consisted of
intravenous daunorubicin days 1, 2, and 3; cytosine arabinoside days 1 to 7;
and etoposide days 1 to 5. Patients were randomized to receive subcutaneous
NEUPOGEN (n = 259) at a dose of 5 mcg/kg/day or placebo (n = 262) from 24 hours
after the last dose of chemotherapy until neutrophil recovery (ANC ≥
1,000/mm³ for 3 consecutive days or ≥ 10,000/mm³ for 1 day) or for a
maximum of 35 days. The demographic and disease characteristics were balanced
between arms with a median age of 54 (range 16 to 89) years; 54% males; initial
white blood cell count (65% < 25,000/mm³ and 27% > 100,000/mm³); 29%
unfavorable cytogenetics.
The main efficacy endpoint was median duration of severe
neutropenia defined as neutrophil count < 500/mm³. Treatment with NEUPOGEN
resulted in a clinically and statistically significant reduction in median
number of days of severe neutropenia, NEUPOGEN-treated patients 14 days,
placebo-treated patients 19 days (p = 0.0001: difference of 5 days (95% CI:
-6.0, -4.0)). There was a reduction in the median duration of intravenous antibiotic
use, NEUPOGEN-treated patients: 15 days versus placebo-treated patients: 18.5
days; a reduction in the median duration of hospitalization, NEUPOGEN-treated
patients: 20 days versus placebo-treated patients: 25 days.
There were no statistically significant differences
between the NEUPOGEN and the placebo groups in complete remission rate (69% -
NEUPOGEN, 68% - placebo), median time to progression of all randomized patients
(165 days - NEUPOGEN, 186 days - placebo), or median overall survival (380 days
- NEUPOGEN, 425 days - placebo).
Patients With Cancer Undergoing Bone Marrow
Transplantation
The safety and efficacy of NEUPOGEN to reduce the
duration of neutropenia in patients with nonmyeloid malignancies undergoing
myeloablative chemotherapy followed by autologous bone marrow transplantation
was evaluated in 2 randomized controlled trials of patients with lymphoma
(Study 6 and Study 9). The safety and efficacy of NEUPOGEN to reduce the
duration of neutropenia in patients undergoing myeloablative chemotherapy
followed by allogeneic bone marrow transplantation was evaluated in a
randomized placebo-controlled trial (Study 10).
In Study 6, patients with Hodgkin's disease received a
preparative regimen of intravenous cyclophosphamide, etoposide, and BCNU
(“CVP”), and patients with non-Hodgkin's lymphoma received intravenous BCNU,
etoposide, cytosine arabinoside and melphalan (“BEAM”). There were 54 patients
randomized 1:1:1 to control, NEUPOGEN 10 mcg/kg/day, and NEUPOGEN 30 mcg/kg/day
as a 24-hour continuous infusion starting 24 hours after bone marrow infusion
for a maximum of 28 days. The median age was 33 (range 17 to 57) years; 56%
males; 69% Hodgkin's disease and 31% non-Hodgkin's lymphoma.
The main efficacy endpoint was duration of severe
neutropenia ANC < 500/mm³. A statistically significant reduction in the
median number of days of severe neutropenia (ANC < 500/mm³) occurred in the
NEUPOGEN-treated groups versus the control group (23 days in the control groupâ
11 days in the 10 mcg/kg/day group, and 14 days in the 30 mcg/kg/day group [11
days in the combined treatment groupsâ p = 0.004]).
In Study 9, patients with Hodgkin's disease and
non-Hodgkin's lymphoma received a preparative regimen of intravenous
cyclophosphamide, etoposide, and BCNU (“CVP”). There were 43 evaluable patients
randomized to continuous subcutaneous infusion NEUPOGEN 10 mcg/kg/day (n = 19),
NEUPOGEN 30 mcg/kg/day (n = 10) and no treatment (n = 14) starting the day
after marrow infusion for a maximum of 28 days. The median age was 33 (range 17
to 56) years; 67% males; 28% Hodgkin's disease and 72% non-Hodgkin's lymphoma.
The main efficacy endpoint was duration of severe
neutropenia. There was statistically significant reduction in the median number
of days of severe neutropenia (ANC < 500/mm³) in the NEUPOGEN-treated groups
versus the control group (21.5 days in the control group versus 10 days in the
NEUPOGEN-treated groups, p < 0.001). The number of days of febrile
neutropenia was also reduced significantly in this study (13.5 days in the
control group versus 5 days in the NEUPOGEN-treated groupsâ p < 0.0001).
In Study 10, 70 patients scheduled to undergo bone marrow
transplantation for multiple underlying conditions using multiple preparative
regimens were randomized to receive NEUPOGEN 300 mcg/m²/day (n = 33) or placebo
(n = 37) days 5 through 28 after marrow infusion. The median age was 18 (range
1 to 45) years, 56% males. The underlying disease was: 67% hematologic
malignancy, 24% aplastic anemia, 9% other. A statistically significant
reduction in the median number of days of severe neutropenia occurred in the
treated group versus the control group (19 days in the control group and 15
days in the treatment groupâ p < 0.001) and time to recovery of ANC to
≥ 500/mm³ (21 days in the control group and 16 days in the treatment
groupâ p < 0.001).
Patients Undergoing Autologous Peripheral Blood
Progenitor Cell Collection And Therapy
The safety and efficacy of NEUPOGEN to mobilize
autologous peripheral blood progenitor cells for collection by leukapheresis
was supported by the experience in uncontrolled trials, and a randomized trial
comparing hematopoietic stem cell rescue using NEUPOGEN mobilized autologous
peripheral blood progenitor cells to autologous bone marrow (Study 11).
Patients in all these trials underwent a similar mobilization/collection
regimen: NEUPOGEN was administered for 6 to 7 daysâ in most cases the apheresis
procedure occurred on days 5â 6, and 7. The dose of NEUPOGEN ranged between 10
to 24 mcg/kg/day and was administered subcutaneously by injection or continuous
intravenous infusion.
Engraftment was evaluated in 64 patients who underwent
transplantation using NEUPOGEN mobilized autologous hematopoietic progenitor
cells in uncontrolled trials. Two of the 64 patients (3%) did not achieve the
criteria for engraftment as defined by a platelet count ≥ 20â000/mm³ by
day 28. In clinical trials of NEUPOGEN for the mobilization of hematopoietic
progenitor cellsâ NEUPOGEN was administered to patients at doses between 5 to
24 mcg/kg/day after reinfusion of the collected cells until a sustainable ANC
(≥ 500/mm³) was reached. The rate of engraftment of these cells in the
absence of NEUPOGEN post transplantation has not been studied.
Study 11 was a randomized, unblinded study of patients
with Hodgkin's disease or non-Hodgkin's lymphoma undergoing myeloablative
chemotherapyâ 27 patients received NEUPOGEN-mobilized autologous hematopoietic
progenitor cells and 31 patients received autologous bone marrow. The
preparative regimen was intravenous BCNU, etoposide, cytosine arabinoside and
melphalan (“BEAM”). Patients received daily NEUPOGEN 24 hours after stem cell
infusion at a dose of 5 mcg/kg/day. The median age was 33 (range 1 to 59)
years; 64% males; 57% Hodgkin's disease and 43% non-Hodgkin's lymphoma. The
main efficacy endpoint was number of days of platelet transfusions. Patients
randomized to NEUPOGEN-mobilized autologous peripheral blood progenitor cells
compared to autologous bone marrow had significantly fewer days of platelet
transfusions (median 6 vs 10 days).
Patients With Severe Chronic Neutropenia
The safety and efficacy of NEUPOGEN to reduce the
incidence and duration of sequelae of neutropenia (that is feverâ infections,
oropharyngeal ulcers) in symptomatic adult and pediatric patients with
congenital neutropeniaâ cyclic neutropeniaâ or idiopathic neutropenia was
established in a randomized controlled trial conducted in patients with severe
neutropenia (Study 7).
Patients eligible for Study 7 had a history of severe
chronic neutropenia documented with an ANC < 500/mm³ on three occasions
during a 6-month period, or in patients with cyclic neutropenia 5 consecutive
days of ANC < 500/mm³ per cycle. In addition, patients must have experienced
a clinically significant infection during the previous 12 months. Patients were
randomized to a 4-month observation period followed by NEUPOGEN treatment or
immediate NEUPOGEN treatment. The median age was 12 years (range 7 months to 76
years); 46% males; 34% idiopathic, 17% cyclic and 49% congenital neutropenia.
NEUPOGEN was administered subcutaneously. The dose of
NEUPOGEN was determined by the category of neutropenia. Initial dose of
NEUPOGEN:
- Idiopathic neutropenia: 3.6 mcg/kg/day
- Cyclic neutropenia: 6 mcg/kg/day
- Congenital neutropenia: 6 mcg/kg/day divided 2 times per
day
The dose was increased incrementally to 12 mcg/kg/day
divided 2 times per day if there was no response.
The main efficacy endpoint was response to NEUPOGEN
treatment. ANC response from baseline (< 500/mm³) was defined as follows:
- Complete response: median ANC > 1,500/mm³
- Partial response: median ANC ≥ 500/mm³ and ≤
1,500/mm³ with a minimum increase of 100%
- No response: median ANC < 500/mm³
There were 112 of 123 patients who demonstrated a
complete or partial response to NEUPOGEN treatment.
Additional efficacy endpoints included a comparison
between patients randomized to 4 months of observation and patients receiving
NEUPOGEN of the following parameters:
- incidence of infection
- incidence of fever
- duration of fever
- incidence, duration, and severity of oropharyngeal ulcers
- number of days of antibiotic use
The incidence for each of these 5 clinical parameters was
lower in the NEUPOGEN arm compared to the control arm for cohorts in each of
the 3 major diagnostic categories. An analysis of variance showed no
significant interaction between treatment and diagnosisâ suggesting that
efficacy did not differ substantially in the different diseases. Although
NEUPOGEN substantially reduced neutropenia in all patient groupsâ in patients
with cyclic neutropeniaâ cycling persisted but the period of neutropenia was
shortened to 1 day.
Patients Acutely Exposed To Myelosuppressive Doses Of Radiation
(Hematopoietic Syndrome Of Acute Radiation Syndrome)
Efficacy studies of NEUPOGEN could not be conducted in
humans with acute radiation syndrome for ethical and feasibility reasons.
Approval of this indication was based on efficacy studies conducted in animals
and data supporting the use of NEUPOGEN for other approved indications [see DOSAGE
AND ADMINISTRATION].
Because of the uncertainty associated with extrapolating
animal efficacy data to humans, the selection of human dose for NEUPOGEN is
aimed at providing exposures to filgrastim that exceed those observed in animal
efficacy studies. The 10 mcg/kg daily dose is selected for humans exposed to
myelosuppressive doses of radiation because the exposure associated with such a
dose is expected to exceed the exposure associated with a 10 mcg/kg dose in
non-human primates [see Pharmacokinetics]. The safety of NEUPOGEN at a
daily dose of 10 mcg/kg has been assessed on the basis of clinical experience
in approved indications.
The efficacy of NEUPOGEN was studied in a randomized,
blinded, placebo-controlled study in a non-human primate model of radiation
injury. The planned sample size was 62 animals, but the study was stopped at
the interim analysis with 46 animals because efficacy was established. Rhesus
macaques were randomized to a control (n = 22) or treated (n = 24) group.
Animals were exposed to total body irradiation of 7.4 ± 0.15 Gy delivered at
0.8 ± 0.03 Gy/min, representing a dose that would be lethal in 50% of animals
by 60 days of follow-up (LD50/60). Starting on day 1 after irradiation, animals
received daily subcutaneous injections of placebo (5% dextrose in water) or
filgrastim (10 mcg/kg/day). Blinded treatment was stopped when one of the
following criteria was met: ANC ≥ 1,000/mm³ for 3 consecutive days, or
ANC ≥ 10,000/mm³ for more than 2 consecutive days within study day 1 to
5, or ANC ≥ 10,000/mm³ any time after study day 5. Animals received
medical management consisting of intravenous fluids, antibiotics, blood
transfusions, and other support as required.
Filgrastim significantly (at 0.023 level of significance)
reduced 60-day mortality in the irradiated non-human primates: 21% mortality
(5/24) in the filgrastim group compared to 59% mortality (13/22) in the control
group.