CLINICAL PHARMACOLOGY
Microbiology
Mechanism Of Action
The active component of ABELCET® , amphotericin B, acts by binding to sterols in the cell membrane
of susceptible fungi, with a resultant change in the permeability of the membrane. Mammalian cell
membranes also contain sterols, and damage to human cells is believed to occur through the same
mechanism of action.
Activity In Vitro And In Vivo
ABELCET® shows in vitro activity against Aspergillus sp. (n=3) and Candida sp. (n=10), with MICs
generally <1 μg/mL. Depending upon the species and strain of Aspergillus and Candida tested,
significant in vitro differences in susceptibility to amphotericin B have been reported (MICs ranging
from 0.1 to >10 μg/mL). However, standardized techniques for susceptibility testing for antifungal
agents have not been established, and results of susceptibility studies do not necessarily correlate with
clinical outcome.
ABELCET® is active in animal models against Aspergillus fumigatus, Candida albicans, C. guillermondii,C. stellatoideae, and C. tropicalis, Cryptococcus sp., Coccidioidomyces sp., Histoplasma sp., and
Blastomyces sp. in which end-points were clearance of microorganisms from target organ(s) and/or
prolonged survival of infected animals.
Drug Resistance
Fungal species with decreased susceptibility to amphotericin B have been isolated after serial passage
in culture media containing the drug, and from some patients receiving prolonged therapy. Although the
relevance of drug resistance to clinical outcome has not been established, fungal species which are
resistant to amphotericin B may also be resistant to ABELCET® .
Pharmacokinetics
The assay used to measure amphotericin B in the blood after the administration of ABELCET® does not
distinguish amphotericin B that is complexed with the phospholipids of ABELCET® from amphotericin
B that is uncomplexed.
The pharmacokinetics of amphotericin B after the administration of ABELCET® are nonlinear. Volume
of distribution and clearance from blood increase with increasing dose of ABELCET® , resulting in
less than proportional increases in blood concentrations of amphotericin B over a dose range of 0.6-5
mg/kg/day. The pharmacokinetics of amphotericin B in whole blood after the administration of
ABELCET® and amphotericin B desoxycholate are:
Pharmacokinetic Parameters of Amphotericin B in Whole Blood
in Patients Administered Multiple Doses of ABELCET® or Amphotericin B Desoxycholate
Pharmacokinetic Parameter |
ABELCET® 5 mg/kg/day
for 5-7 days Mean ± SD |
Amphotericin B
0.6 mg/kg/day for 42 daysa
Mean ± SD |
Peak Concentration ( μg/mL) |
1.7 ± 0.8 (n=10)b |
1.1 ± 0.2 (n=5) |
Concentration at End of Dosing Interval
(μg/mL) |
0.6 ± 0.3 (n=10b |
0.4 ± 0.2 (n=5) |
Area Under Blood Concentration-Time
Curve
(AUC0-24h) (μg*h/mL) |
14.0 ± 7.0 (n=14)b,c |
17.1 ± 5 (n=5) |
Clearance (mL/h*kg) |
436.0.± 188.5 (n=14)b,c |
38.0 ± 15 (n=5) |
Apparent Volume of Distribution
(Vdarea) (L/kg) |
131.0.± 57.7 (n=8)c |
5.0.± 2.8 (n=5) |
Terminal Elimination Half-Life (h) |
173.4 ± 78.0 (n=8)c |
91.1 ± 40.9 (n=5) |
Amount Excreted in Urine Over 24 h After Last Dose (% of dose) |
0.9 ± 0.4 (n=8)c |
9.6 ± 2.5 (n=8) |
a Data from patients with mucocutaneous leishmaniasis. Infusion rate was 0.25 mg/kg/h.
b Data from studies in patients with cytologically proven cancer being treated with chemotherapy or
neutropenic patients with
presumed or proven fungal infection. Infusion rate was 2.5 mg/kg/h.
c Data from patients with mucocutaneous leishmaniasis. Infusion rate was 4 mg/kg/h.
d Percentage of dose excreted in 24 hours after last dose. |
The large volume of distribution and high clearance from blood of amphotericin B after the
admistration of ABELCET® probably reflect uptake by tissues. The long terminal elimination half-life
probably reflects a slow redistribution from tissues. Although amphotericin B is excreted slowly, there
is little accumulation in the blood after repeated dosing. AUC of amphotericin B increased
approximately 34% from day 1 after the administration of ABELCET® 5 mg/kg/day for 7 days. The
effect of gender or ethnicity on the pharmacokinetics of ABELCET® has not been studied.
Tissue concentrations of amphotericin B have been obtained at autopsy from one heart transplant patient
who received three doses of ABELCET® at 5.3 mg/kg/day:
Concentration in Human Tissues
Organ |
Amphotericin B
Tissue Concentration (μg/g) |
Spleen |
290.0 |
Lung |
222.0 |
Liver |
196.0 |
Lymph Node |
7.6 |
Kidney |
6.9 |
Heart 0 |
5. |
Brain |
1.6 |
This pattern of distribution is consistent with that observed in preclinical studies in dogs in which
greatest concentrations of amphotericin B after ABELCET® administration were observed in the liver,
spleen, and lung; however, the relationship of tissue concentrations of amphotericin B to its biological
activity when administered as ABELCET® is unknown.
Special Populations
Hepatic Impairment
The effect of hepatic impairment on the disposition of ABELCET® is not known.
Renal Impairment
The effect of renal impairment on the disposition of ABELCET® is not known. The
effect of dialysis on the elimination of ABELCET® has not been studied; however, amphotericin B is
not removed by hemodialysis when administered as amphotericin B desoxycholate.
Pediatric And Elderly Patients
The pharmacokinetics and pharmacodynamics of pediatric patients (≤16
years of age) and elderly patients (≥65 years of age) have not been studied.
Description Of Clinical Studies
Fungal Infections
Data from 473 patients were pooled from three open-label studies in which ABELCET® was provided
for the treatment of patients with invasive fungal infections who were judged by their physicians to be
refractory to or intolerant of conventional amphotericin B, or who had preexisting nephrotoxicity.
Results of these studies demonstrated effectiveness of ABELCET® in the treatment of invasive fungal
infections as a second line therapy.
Patients were defined by their individual physician as being refractory to or failing conventional
amphotericin B therapy based on overall clinical judgement after receiving a minimum total dose of 500
mg of amphotericin B. Nephrotoxicity was defined as a serum creatinine that had increased to >2.5
mg/dL in adults and >1.5 mg/dL in pediatric patients, or a creatinine clearance of <25 mL/min while
receiving conventional amphotericin B therapy.
Of the 473 patients, four were enrolled more than once; each enrollment contributed separately to the
denominator. The median age was 39 years (range of <1 to 93 years); 307 patients were male and 166
female. Patients were Caucasian (381, 81%), African-American (41, 9%), Hispanic (27, 6%), Asian (10,
2%), and various other races (14, 3%). The median baseline neutrophil count was 4,000 PMN/mm3; of
these, 101 (21%) had a baseline neutrophil count <500/mm3 .
Two-hundred eighty-two patients of the 473 patients were considered evaluable for response to
therapy; the other 191 patients were excluded on the basis of unconfirmed diagnosis, confounding
factors, concomitant systemic antifungal therapy, or receiving 4 doses or less of ABELCET® . For
evaluable patients, the following fungal infections were treated (n=282): aspergillosis (n=111),
candidiasis (n=87), zygomycosis (n=25), cryptococcosis (n=16), and fusariosis (n=11). There were
fewer than 10 evaluable patients for each of several other fungal species treated.
For each type of fungal infection listed above there were some patients successfully treated. However,
in the absence of controlled studies it is unknown how response would have compared to either
continuing conventional amphotericin B therapy or the use of alternative antifungal agents.
Renal Function
Patients with aspergillosis who initiated treatment with ABELCET® when serum
creatinine was above 2.5 mg/dL experienced a decline in serum creatinine during treatment (Figure 1).
Serum creatinine levels were also lower during treatment with ABELCET® when compared to the
serum creatinine levels of patients treated with conventional amphotericin B in a retrospective historical
control study. Meaningful statistical testing of the differences between these two groups is precluded
since these data were obtained from two separate studies.
Figure 1: Changes in Mean Serum Creatinine Over Time
Patients with Aspergillosis and Serum Creatinine >2.5 mg/dL at Baseline
[ ]= Number of patients at each time point.
Note: These curves do not represent the clinical course of a given patient, but that of an open-label
cohort of patients.
Figure 2: Changes in Mean Serum Creatinine Over Time
Patients with Fungal Infections and Serum Creatinine >2.5 mg/dL at Baseline
[ ]= Number of patients at each time point.
Note: These curves do not represent the clinical course of a given patient, but that of an open-label
cohort of patients.
In a randomized study of ABELCET® for the treatment of invasive candidiasis in patients with normal
baseline renal function, the incidence of nephrotoxicity was significantly less for ABELCET® at a dose
of 5 mg/kg/day than for conventional amphotericin B at a dose of 0.7 mg/kg/day.
Despite generally less nephrotoxicity of ABELCET® observed at a dose of 5 mg/kg/day compared
with conventional amphotericin B therapy at a dose range of 0.6-1 mg/kg/day, dose-limiting renal
toxicity may still be observed with ABELCET® . Renal toxicity of doses greater than 5 mg/kg/day of
ABELCET® has not been formally studied.