Excretion: Posaconazole is predominantly eliminated in the feces (71% of the radiolabeled dose up to 120 hours) with the major component eliminated as parent drug (66% of the radiolabeled dose). Renal clearance is a minor elimination pathway, with 13% of the radiolabeled dose excreted in urine up to 120 hours (<0.2% of the radiolabeled dose is parent drug).
 
Posaconazole delayed-release tablet is eliminated with a mean half-life (t½) ranging between 26 to 31 hours.
 
Posaconazole oral suspension is eliminated with a mean half-life (t½) of 35 hours (range: 20-66 hours).

12.4 Microbiology

Mechanism of Action:
 
Posaconazole blocks the synthesis of ergosterol, a key component of the fungal cell membrane, through the inhibition of cytochrome P-450 dependent enzyme lanosterol 14α-demethylase responsible for the conversion of lanosterol to ergosterol in the fungal cell membrane. This results in an accumulation of methylated sterol precursors and a depletion of ergosterol within the cell membrane thus weakening the structure and function of the fungal cell membrane. This may be responsible for the antifungal activity of posaconazole.

Activity in vitro:
 
Posaconazole has in vitro activity against Aspergillus fumigatus and Candida albicans, including Candida albicans isolates from patients refractory to itraconazole or fluconazole or both drugs [see Clinical Studies (14), Indications and Usage (1) and Dosage and Administration (2)]. However, correlation between the results of susceptibility tests and clinical outcome has not been established. Posaconazole interpretive criteria (breakpoints) have not been established for any fungus.

Drug Resistance:
 
Clinical isolates of Candida albicans and Candida glabrata with decreased susceptibility to posaconazole were observed in oral swish samples taken during prophylaxis with posaconazole and fluconazole, suggesting a potential for development of resistance. These isolates also showed reduced susceptibility to other azoles, suggesting cross-resistance between azoles. The clinical significance of this finding is not known.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility
 
No drug-related neoplasms were recorded in rats or mice treated with posaconazole for 2 years at doses higher than the clinical dose. In a 2-year carcinogenicity study, rats were given posaconazole orally at doses up to 20 mg/kg (females), or 30 mg/kg (males). These doses are equivalent to 3.9- or 3.5-times the exposure achieved with a 400-mg BID oral suspension regimen, respectively, based on steady-state AUC in healthy volunteers administered a high-fat meal (400-mg BID oral suspension regimen). In the mouse study, mice were treated at oral doses up to 60 mg/kg/day or 4.8-times the exposure achieved with a 400-mg BID oral suspension regimen.
 
Posaconazole was not genotoxic or clastogenic when eva luated in bacterial mutagenicity (Ames), a chromosome aberration study in human peripheral blood lymphocytes, a Chinese hamster ovary cell mutagenicity study, and a mouse bone marrow micronucleus study.
 
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