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Antimicrobial Agents and Chemotherapy, February 2004, p. 384-387, Vol. 48, No. 2
0066-4804/04/$08.00+0 DOI: 10.1128/AAC.48.2.384-387.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Department of Medicine, Pediatrics,1 Duke Clinical Research Institute, Division of Infectious Diseases, Duke University Medical Center, Durham, North Carolina,2 Drug Discovery, J. Uriach & Cia, Palau-solità i Plegamans, Barcelona, Spain3
Received 23 July 2003/ Returned for modification 2 October 2003/ Accepted 14 October 2003
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0.0012 to 1.25 µg/ml, with the MICs for most isolates being between 0.039 and 0.156 µg/ml. Isolates were from human immunodeficiency virus (HIV)-infected and non-HIV-infected patients and were of serotypes A, B, and C; and the fluconazole MICs for some of the isolates were elevated. Infected rabbits were treated with either fluconazole or albaconazole at dosages ranging from 5 to 80 mg/kg of body weight/day. The peak concentrations of albaconazole in serum and cerebrospinal fluid (CSF) averaged 4.14 and 0.62 µg/ml, respectively, in animals receiving 80 mg/kg/day. Comparison of the concentrations in serum and CSF suggested a level of CSF penetration of approximately 15%. Despite limited penetration into the subarachnoid space, at all three doses tested albaconazole was as effective as fluconazole for the treatment of cryptococcal meningitis in rabbits. |
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The new triazole albaconazole (J. Uriach & Cía. S.A., Barcelona, Spain) (Fig. 1) is known to possess in vitro potency, broad-spectrum antifungal activity, good pharmacokinetics, and excellent oral bioavailability (1, 19). In this study we examined its in vitro and in vivo activities against the basidiomycetous pathogen C. neoformans. The activity of albaconazole was compared to that of fluconazole in vitro, and albaconazole was found to be very active against all 12 C. neoformans isolates tested, including an isolate for which the fluconazole MIC was 64 µg/ml. The in vivo efficacy of albaconazole was evaluated by using a standardized rabbit model of cryptococcal meningitis (11-17, 21, 24). The efficacy of albaconazole was compared to that of fluconazole, an agent with which there is significant experience for the prophylaxis, suppression, and treatment of cryptococcosis in humans and animals (4, 8, 9, 18, 20). Fluconazole and albaconazole were found to have similar therapeutic activities in this experimental model.
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FIG. 1. Chemical structure of albaconazole.
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Antifungal agents. For in vitro testing, 2 mg of albaconazole was dissolved in 2 ml of 100% dimethyl sulfoxide, which yielded a concentration of 1,000 µg/ml (50x solution), and was stored by a standard protocol (5). For in vivo testing at 80 mg/kg of body weight/day, albaconazole was prepared fresh daily by suspending 3.024 g in 27 ml of sterile 0.2% carboxymethyl cellulose with 1% Tween 80. Lower dosages were prepared accordingly so that the vehicle volume given in each regimen was the same. The suspension was made by first grinding drug with a small amount of 0.2% carboxymethyl cellulose-1% Tween in a mortar and pestle and then gradually adding the remainder of the solvent vehicle. The albaconazole suspension was administered by oral gavage with a 3-in. 18-gauge gavage needle. Fluconazole (a 40-mg/ml oral suspension; Diflucan; Pfizer, New York, N.Y.) was given daily by gavage at a dose of 5, 20, or 80 mg/kg.
Organisms. C. neoformans H99 (DUMC 135.97) was the clinical isolate used to establish meningitis in the rabbits (11, 14, 21). Eleven additional C. neoformans isolates chosen for in vitro susceptibility testing consisted of isolates from both AIDS and non-AIDS patients of serotypes A, B, and C; and the fluconazole MICs for the various isolates covered a broad range. The isolates studied were serotype B isolate DUMC 114.95; serotype C isolate 119.95; and serotype A isolates 109.97, 251.86, 124.96, 163.99, 133.95, 114.96, 135.97, 123.96, 158.03, and 125.96.
In vitro susceptibility testing. An approved method for yeast susceptibility testing, as modified for C. neoformans, was followed (7). This broth macrodilution method specifies the use of an inoculum of approximately 103 CFU/ml in RPMI 1640 medium with 3-(N-morpholino)propanesulfonic acid incubated at 35°C for 72 h. A total of 100 µl of each inoculum was plated so that an exact baseline count for each isolate could be established. The MIC endpoint for azole compounds is defined as an 80% reduction in growth compared to the growth of the drug-free control. For determination of fungicidal concentrations, tubes showing no growth were vortexed and a 100-µl aliquot from each was plated onto Sabouraud agar plates. The lowest drug concentration that killed at least 97% of the baseline inoculum was recorded as the minimum fungicidal concentration (MFC).
Antimicrobial assay. The concentration of albaconazole in serum and cerebrospinal fluid (CSF) samples was measured by a bioassay with yeast nitrogen base, agar diffusion (bioassay) plates, and Candida kefyr ATCC 46764 (3). Known concentrations of albaconazole were dissolved in dimethyl sulfoxide and prepared in serum and CSF obtained from infected, untreated control rabbits. The CSF standards contained albaconazole at concentrations ranging from 0.03125 to 1.0 µg/ml, and the serum standards contained albaconazole at concentrations ranging from 0.625 to 5 µg/ml. Controls included rabbit serum and CSF. The data were plotted by using Microsoft Excel software, and concentrations were calculated from the R2 value.
Production of cryptococcal meningitis. Beginning 1 day prior to inoculation and for the duration of the experiment, all animals received a daily intramuscular injection of hydrocortisone acetate (5.0 mg/kg; Sigma, St. Louis, Mo.). C. neoformans (H99) was grown at 35°C for 3 days on Sabouraud agar plates with chloramphenicol, harvested with a cotton swab, and suspended in 0.015 M phosphate-buffered saline at pH 7.4 to a density of 1.0 x 109 CFU/ml, as verified by quantitative culture. The rabbits were sedated and inoculated intracisternally with 0.3 ml of the yeast inoculum. On predetermined days following inoculation, intracisternal taps were performed, and approximately 0.5 ml of CSF was aspirated. The CSF was diluted in phosphate-buffered saline and cultured on Sabouraud agar with chloramphenicol. The results were expressed as the log10 CFU per milliliter of CSF.
Treatment regimens. Treatment regimens of 80 mg/kg/day for 14 days, 20 mg/kg/day for 23 days, or 5 mg/kg/day for 19 days were begun 2 days after inoculation of the rabbits. Six rabbits were assigned to the albaconazole group, and five rabbits each were assigned to the fluconazole and the untreated control group for each dose. The experiment with albaconazole at 5 mg/kg did not include an untreated control group. This exclusion was based on findings of consistent mortality in the control rabbits used in the experiments with the other two dosages and thus allowed us to minimize the number of deaths.
Statistical methods. Survival time data were analyzed by Kaplan-Meier curve analysis; P values derived from Kaplan-Meier curves are based on log-rank (nonparametric) testing. Fisher's exact test was used for categorical data. Because multiple tests were performed, the Bonferroni correction was used to interpret P values. The analysis was repeated by the Wilcoxon rank-sum test for continuous variables with multivariable regression modeling to account for multiple observations, and the results (not presented) were similar. In order to compare the organism burdens achieved with fluconazole and albaconazole, the data were analyzed by the generalized estimating equation (GEE). Analysis by GEE is a regression technique that accounts for multiple observations for each individual animal. An unstructured within-group correlation matrix was used in the regression with GEE. The outcome was the organism concentration, and the independent variable was the treatment (fluconazole or albaconazole).
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TABLE 1. MICs and MFCs of fluconazole and albaconazole for 12 isolates of C. neoformans
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TABLE 2. Albaconazole concentrations in serum and CSF of rabbits with cryptococcal meningitis
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FIG. 2. Results of treatment of cryptococcal meningitis with albaconazole or fluconazole or no treatment (controls). (a) Dosing at 80 mg/kg/day; (b) dosing at 20 mg/kg/day; (c) dosing at 5 mg/kg/day.
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FIG. 3. Comparison of survival of rabbits treated with albaconazole or fluconazole at all dosages or not treated (controls). Kaplan-Meier survival estimates predict a survival advantage for treated animals (P < 0.001).
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For in vivo testing we used a model of cryptococcal meningitis in immunosuppressed rabbits, and we standardized the model using C. neoformans isolate H99. The activity of albaconazole was compared to that of fluconazole, the azole with which there is the most experience in the management of cryptococcal infections in humans and animals. From pharmacokinetic measurements of albaconazole, we determined that the concentrations achievable in rabbit serum and CSF when a dose of 80 mg/kg was used were approximately 4 and 0.5 µg/ml, respectively. This concentration is more than 100-fold (serum) and 10-fold (CSF) higher than the MICs for most clinical isolates tested, including isolate H99, which was used for the in vivo studies.
Three dosage regimens were compared in the treatment experiments, and the results demonstrated that all doses of albaconazole and fluconazole have equivalent therapeutic activities in this animal model. In comparison to the C. neoformans yeast counts in the CSF of untreated animals, both albaconazole and fluconazole significantly reduced the yeast counts in the CSF over 2 weeks of treatment and produced a survival advantage. There was slow, consistent killing of C. neoformans over 2 weeks of treatment, but the subarachnoid space of most animals was not sterilized by the end of treatment.
Our interpretation of the results suggests that the pharmacokinetics and the potencies of these two triazoles are proportional for the treatment cryptococcosis. Specifically, fluconazole at the 80-mg/kg dose produces much higher concentrations in serum (65 to 75 µg/ml) and CSF (40 to 45 µg/ml) at 1 to 2 h postdosing (15). This translates into a level of penetration into CSF of 60%. These levels are approximately 10-fold higher than the fluconazole MIC for isolate H99. Similarly, albaconazole at the 80-mg/kg dose achieved concentrations in CSF (0.5 µg/ml) that were more than 10-fold higher than the albaconazole MIC for H99. However, albaconazole concentrations in CSF did not approach the MFC for H99 (20 µg/ml), and this might be the reason that albaconazole, like fluconazole, exhibited a slow onset of action and a gradual reduction in the yeast counts in CSF rather than rapid killing. Albaconazole possesses potent in vitro activity against C. neoformans isolates and shows signs of some fungicidal activity against certain isolates. It is possible that cryptococcal isolates in the subarachnoid space for which MFCs are lower might be killed more rapidly by albaconazole treatment. The rabbit model of cryptococcal meningitis has been an accurate predictor of drug activity in humans. Thus, this study suggests that further in vivo investigations of this triazole for the treatment of fluconazole-resistant isolates of C. neoformans in the rabbit are warranted and that albaconazole could potentially be effective for the treatment of human cryptococcosis.
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