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Antimicrobial Agents and Chemotherapy, October 2001, p. 2845-2855, Vol. 45, No. 10
Immunocompromised Host Section, Pediatric
Oncology Branch, National Cancer Institute,1
Surgery Branch, Veterinary Resources Program, National Center
for Research Resources,2 and
Pharmacokinetics Research Laboratory, Pharmacy Department,
Warren Grant Magnuson Clinical Center,3 National
Institutes of Health, Bethesda, Maryland
Received 7 November 2000/Returned for modification 30 April
2001/Accepted 20 July 2001
The compartmental pharmacokinetics of anidulafungin (VER-002;
formerly LY303366) in plasma were characterized with normal rabbits,
and the relationships between drug concentrations and antifungal
efficacy were assessed in clinically applicable infection models in
persistently neutropenic animals. At intravenous dosages ranging from
0.1 to 20 mg/kg of body weight, anidulafungin demonstrated linear
plasma pharmacokinetics that fitted best to a three-compartment open
pharmacokinetic model. Following administration over 7 days, the mean
(± standard error of the mean) peak plasma concentration (Cmax) increased from 0.46 ± 0.02 µg/ml at
0.1 mg/kg to 63.02 ± 2.93 µg/ml at 20 mg/kg, and the mean area
under the concentration-time curve from 0 h to infinity
(AUC0-
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.10.2845-2855.2001
Pharmacokinetic and Pharmacodynamic Modeling of Anidulafungin
(LY303366): Reappraisal of Its Efficacy in Neutropenic Animal Models of
Opportunistic Mycoses Using Optimal Plasma Sampling
) rose from 0.71 ± 0.04 to 208.80 ± 24.21 µg · h/ml. The mean apparent volume of distribution at
steady state (Vss) ranged from 0.953 ± 0.05 to 1.636 ± 0.22 liter/kg (nonsignificant [NS]), and
clearance ranged from 0.107 ± 0.01 to 0.149 ± 0.00 liter/kg/h (NS). Except for a significant prolongation of the terminal
half-life and a trend toward an increased Vss
at the higher end of the dosage range after multiple doses, no
significant differences in pharmacokinetic parameters were noted in
comparison to single-dose administration. Concentrations in tissue at
trough after multiple dosing (0.1 to 10 mg/kg/day) were highest in lung
and liver (0.85 ± 0.16 to 32.64 ± 2.03 and 0.32 ± 0.05 to 43.76 ± 1.62 µg/g, respectively), followed by spleen
and kidney (0.24 ± 0.65 to 21.74 ± 1.86 and <0.20 to
16.92 ± 0.56, respectively). Measurable concentrations in brain
tissue were found at dosages of
0.5 mg/kg (0.24 ± 0.02 to
3.90 ± 0.25). Implementation of optimal plasma sampling in persistently neutropenic rabbit infection models of disseminated candidiasis and pulmonary aspergillosis based on the Bayesian approach
and model parameters from normal animals as priors revealed a
significantly slower clearance (P < 0.05 for all
dosage groups) with a trend toward higher AUC0-24 values,
higher plasma concentrations at the end of the dosing interval, and a
smaller volume of distribution (P < 0.05 to 0.193 for
the various comparisons among dosage groups). Pharmacodynamic modeling
using the residual fungal tissue burden in the main target sites as the
primary endpoint and Cmax,
AUC0-24, time during the dosing interval of 24 h with
plasma drug concentration equaling or exceeding the MIC or the minimum
fungicidal concentration for the isolate, and tissue concentrations as
pharmacodynamic parameters showed predictable pharmacokinetic-pharmacodynamic relationships in experimental disseminated candidiasis that fitted well with an inhibitory sigmoid maximum effect pharmacodynamic model (r2, 0.492 to 0.819). However, no concentration-effect relationships were observed
in experimental pulmonary aspergillosis using the residual fungal
burden in lung tissue and survival as parameters of antifungal
efficacy. Implementation of optimal plasma sampling in discriminative
animal models of invasive fungal infections and pharmacodynamic
modeling is a novel approach that holds promise of improving and
accelerating our understanding of the action of antifungal compounds in vivo.
*
Corresponding author. Mailing address:
Immunocompromised Host Section, Pediatric Oncology Branch, National
Cancer Institute, National Institutes of Health, Building 10, Rm.
13N240, 10 Center Dr., Bethesda, MD 20892. Phone: (301) 402-0023. Fax:
(301) 402-0575. E-mail: walsht{at}mail.nih.gov.
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