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Antimicrobial Agents and Chemotherapy, February 1998, p. 459-461, Vol. 42, No. 2
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Rationale for and Efficacy of Prolonged-Interval Treatment
Using Liposome-Encapsulated Amikacin in Experimental
Mycobacterium avium Infection
S.
Leitzke,1,*
W.
Bucke,2
K.
Borner,3
R.
Müller,2
H.
Hahn,1 and
S.
Ehlers4
Department of Infectious Diseases, Benjamin
Franklin University Clinic, Free University of Berlin, D-12203
Berlin,1
Department of Pharmaceutical
Technology, Free University of Berlin, D-12169
Berlin,2
Department of Clinical
Chemistry and Clinical Biochemistry, Benjamin Franklin University
Clinic, Free University of Berlin, D-12200
Berlin,3 and
Division of Molecular
Infection Biology, Research Center Borstel, D-23845
Borstel,4 Germany
Received 11 June 1997/Returned for modification 18 August
1997/Accepted 26 September 1997
 |
ABSTRACT |
The potential of liposome-encapsulated antibiotics for prolonging
drug application intervals was investigated by using a murine model of
chronic lethal Mycobacterium avium infection. Liposomal encapsulation of amikacin, but not of ciprofloxacin, resulted in high
and sustained drug levels in infected tissues, exceeding the minimal
inhibitory concentration for M. avium for at least 28 days.
As a consequence, once-weekly and even once-monthly treatments with
liposomal amikacin significantly reduced bacterial replication in
infected tissues and extended the survival time of infected mice.
| |
TEXT |
Mycobacterium avium
continues to cause life-threatening disseminated infections in AIDS
patients (11, 12, 16, 21). Daily multiple-drug therapy must
often be continued throughout life and is frequently accompanied by
major side effects, resulting in poor patient compliance
(2). Therefore, alternative strategies which reduce the
toxicity of the drugs and allow for prolonged application intervals are
needed (1, 15).
Previous studies demonstrated the general usefulness of
liposome-encapsulated drugs in murine models of M. avium
infection (6-9). To capitalize on these findings, the aims
of our study were (i) to define suitable application intervals for
intermittent therapy based on a pharmacokinetic evaluation of drug
accumulation in infected organs and (ii) to establish whether
intermittent therapy with prolonged application intervals would be
effective in experimental M. avium infection.
Pharmacokinetic studies.
Female C57BL/6 mice (6 to 8 weeks old) were injected intravenously either with a single dose
of 600 mg of free or liposome-encapsulated amikacin (Bristol) or with
1,000 mg of free or liposome-encapsulated ciprofloxacin (Bayer).
Liposome encapsulation of the drugs was achieved by a modified ethanol
injection method, as described previously (5).
Two and 24 h following injection, three mice per regimen were
sacrificed and their livers, spleens, and lungs were homogenized in 0.1 N H3PO4. Amikacin levels in the samples were
measured by a fluorescence polarization immunoassay (13),
and ciprofloxacin was measured by high-performance liquid
chromatography analysis (4). The thresholds of detection
were 8 and 4 mg/kg of organ, respectively.
Drug concentrations measured 2 h after injection of
liposome-encapsulated antibiotics were 35.6 ± 9.8 mg of
amikacin/kg of liver, 162.0 ± 14.2 mg of amikacin/kg of spleen,
34.1 ± 2.4 mg of ciprofloxacin/kg of liver, and 69.2 ± 26.2 mg of ciprofloxacin/kg of spleen (means ± standard deviations).
In contrast, 2 h after application of aqueous drug preparations,
amikacin levels were below the level of detection, while ciprofloxacin
was still detectable at 10.2 ± 2.1 mg/kg of liver and 10.7 ± 1.4 mg/kg of spleen. At 24 h postinjection, however, only
liposome-encapsulated amikacin resulted in a sustained accumulation of
drug in the livers and spleens (59.1 ± 7.5 and 194.0 ± 51.0 mg/kg, respectively), while ciprofloxacin concentrations had fallen
below the threshold of detection. Thus, in contrast to previous studies
demonstrating the therapeutic efficacy of liposomal ciprofloxacin in
vitro (17, 18), our data obtained in vivo show a rapid
redistribution of ciprofloxacin from the target tissues, limiting its
therapeutic potential.
Extended pharmacokinetic studies were therefore performed with amikacin
only. For this purpose, amikacin concentrations were
determined in the
livers, spleens, lungs, and kidneys of uninfected
mice at intervals
from 2 h to 28 days following injection of a
single dose of 2,000 or 600 mg of liposome-entrapped or aqueous
amikacin. Two hours after
injection of the larger dose, the levels
of liposome-encapsulated
amikacin in the livers (Fig.
1) and spleens
were up to 30-fold higher
than those of aqueous amikacin.
Throughout
a period of 28 days after administration of liposomal
amikacin,
the drug concentrations in the livers and spleens after
injection
of either dose exceeded 8 mg/kg of organ. By contrast, 2 to
9
h after injection of aqueous amikacin, drug concentrations fell
below the threshold of detection in both organs.
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FIG. 1.
Concentrations of amikacin in the livers and lungs of
C57BL/6 mice at indicated time points after a single intravenous
injection of 600 (circles) or 2,000 (triangles) mg of either liposomal
(closed symbols) or free (open symbols) amikacin. The threshold of
detection is indicated ( ).
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|
With the lungs, administration of liposomal amikacin resulted in
approximately a fivefold-higher drug level at 2 h
postinjection
than administration of aqueous amikacin did. Amikacin
concentrations
fell below the threshold of detection at 9 h after
injection of
either the lower dose of liposomal amikacin or the higher
dose
of the aqueous preparation or at 6 days after injection of the
higher dose of liposomal amikacin (Fig.
1). These pharmacokinetic
studies extend the original findings of Cynamon et al. (
6).
Using rats, Swenson et al. (
19) previously showed that
liposomal
encapsulation of gentamicin resulted in the prolonged
presence
of the drug in the spleens (15 weeks) but not in the lungs (3
days).
Drug accumulation levels and retention times in the kidneys were
similar after injection of liposomal and aqueous amikacin,
showing a
dose-dependent decline throughout the observation period
(data not
shown). The increased drug accumulation in reticuloendothelial
system
organs is therefore unlikely to be accompanied by nephrotoxicity.
Similar conclusions were reached by Tomioka et al. (
20), who
studied the accumulation of free and liposome-entrapped kanamycin
in
the kidneys of mice.
Therapeutic efficacy of liposomal amikacin administered over
prolonged treatment intervals.
To test the therapeutic efficacy of
once-weekly and once-monthly administration of 2,000 mg of liposomal
amikacin during infection, C57BL/6 mice were inoculated intravenously
with 105 CFU of the virulent M. avium strain TMC
724 (a gift from F. Collins, Trudeau Institute, Saranac Lake, N.Y.).
Liposomal amikacin was given intravenously for 6 consecutive weeks or
months, starting on day 7 after infection, and bacterial loads were
monitored in the livers, spleens, and lungs of treated and untreated
mice, as described previously (9, 10). This model of
infection was chosen because it leads to the death of even
immunocompetent mice 120 to 150 days after infection (9).
By the end of therapy, weekly treatment with liposomal amikacin had
reduced the bacterial counts in the livers by more than
2 orders of
magnitude and replication of
M. avium organisms in
the
spleens (data not shown) and lungs had stabilized (Fig.
2).
Thus, a once-weekly treatment
schedule proved to be as effective
as previously reported regimens of
twice-weekly or even daily
injections (
3,
6,
8,
9).
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FIG. 2.
Time course of M. avium infection in the
livers and lungs of C57BL/6 mice treated intravenously once weekly
(closed circles) or once monthly (closed triangles) with 2,000 mg of
liposome-encapsulated amikacin or left untreated (open squares). The
time of death of control infected mice (+), the end of the observation
period after treatment with weekly application intervals
(), and the end of the
observation period after treatment with monthly application intervals
(#) are indicated.
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|
One month after a single injection of liposomal amikacin, the bacterial
loads in the livers were also found to be reduced.
Continuation of the
once-monthly therapy, however, did not further
reduce the bacterial
load (Fig.
2). In the spleens and lungs,
bacterial counts increased
during once-monthly treatment, albeit
at a lower rate than that in
untreated controls. As a reflection
of the low drug levels achieved in
the lungs after administration
of liposomal amikacin, overall treatment
efficacy in the lungs
was poor (Fig.
2) (
7,
8,
14).
Most importantly, monthly treatment led to a significantly prolonged
survival time of the treated animals, which all survived
the
observation period of 7 months, whereas all control infected
animals
died approximately 4 months after time of infection. This
benefit was
also observed when treatment was initiated at an advanced
stage of
infection.
In conclusion, our pharmacokinetic data concerning drug accumulation in
infected organs provided a sound basis for predicting
treatment
results. Since administration of a liposomal preparation
of amikacin
resulted in elevated drug concentrations in target
tissues for up to 28 days, treatment was effective even when given
only once a month. The
potential of liposomal amikacin in the
therapy of
M. avium
infection, i.e., in the substantial extension
of application intervals,
warrants further study with humans.
| |
ACKNOWLEDGMENTS |
We thank Ellen Borner for expert technical assistance.
This work was supported by grant MU 708/9-1 from the Deutsche
Forschungsgemeinschaft.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Infectious Diseases, Benjamin Franklin University Clinic, Free
University of Berlin, Hindenburgdamm 27, D-12203 Berlin, Germany.
Phone: 49-30-8445-3654. Fax: 49-30-8445-3830. E-mail:
Leitzke{at}zedat.fu-berlin.de.
| |
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Antimicrobial Agents and Chemotherapy, February 1998, p. 459-461, Vol. 42, No. 2
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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