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Antimicrobial Agents and Chemotherapy, March 1999, p. 503-509, Vol. 43, No. 3
NeXstar Pharmaceuticals, Inc., Boulder,
Colorado,1 and Sierra Biomedical,
Inc. Sparks, Nevada2
Received 4 May 1998/Returned for modification 23 August
1998/Accepted 1 December 1998
Liposomal aminoglycosides have been shown to have activity against
intracellular infections, such as those caused by Mycobacterium avium. Amikacin in small, low-clearance liposomes (MiKasome) also has curative and prophylactic efficacies against Pseudomonas
aeruginosa and Klebsiella pneumoniae. To develop
appropriate dosing regimens for low-clearance liposomal
amikacin, we studied the pharmacokinetics of liposomal amikacin in
plasma, the level of exposure of plasma to free amikacin, and urinary
excretion of amikacin after the administration of single-dose
(20 mg/kg of body weight) and repeated-dose (20 mg/kg eight times at
48-h intervals) regimens in rhesus monkeys. The clearance of liposomal
amikacin (single-dose regimen, 0.023 ± 0.003 ml
min
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Pharmacokinetics and Urinary Excretion of Amikacin in
Low-Clearance Unilamellar Liposomes after a Single or Repeated
Intravenous Administration in the Rhesus Monkey
1 kg
1; repeated-dose regimen, 0.014 ± 0.001 ml min
1 kg
1) was over 100-fold
lower than the creatinine clearance (an estimate of conventional
amikacin clearance). Half-lives in plasma were longer than those
reported for other amikacin formulations and declined during the
elimination phase following administration of the last dose (from
81.7 ± 27 to 30.5 ± 5 h). Peak and trough (48 h)
levels after repeated dosing reached 728 ± 72 and 418 ± 60 µg/ml, respectively. The levels in plasma remained >180 µg/ml for
6 days after the administration of the last dose. The free amikacin concentration in plasma never exceeded 17.4 ± 1 µg/ml and fell rapidly (half-life, 1.47 to 1.85 h) after the
administration of each dose of liposomal amikacin. This and the low
volume of distribution (45 ml/kg) indicate that the amikacin in plasma
largely remained sequestered in long-circulating liposomes. Less
than half the amikacin was recovered in the urine, suggesting that the
level of renal exposure to filtered free amikacin was reduced, possibly
as a result of intracellular uptake or the metabolism of liposomal
amikacin. Thus, low-clearance liposomal amikacin could be administered
at prolonged (2- to 7-day) intervals to achieve high levels of
exposure to liposomal amikacin with minimal exposure to free amikacin.
*
Corresponding author. Present address: Biologistic
Services, 498 Skytrail Rd., Boulder, CO 80302. Phone: (303) 786-7243. Fax: (303) 786-7243. E-mail:
biopharm{at}worldnet.att.net.
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