NOXAFIL (Page 8 of 10)

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.

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.

Antimicrobial Activity:

Posaconazole has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections [see Indications and Usage (1)].

Microorganisms:

Aspergillus spp. and Candida spp.

Susceptibility Testing:

For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.

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 evaluated 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.

Posaconazole had no effect on fertility of male rats at a dose up to 180 mg/kg (1.7 × the 400-mg BID oral suspension regimen based on steady-state plasma concentrations in healthy volunteers) or female rats at a dose up to 45 mg/kg (2.2 × the 400-mg BID oral suspension regimen).

13.2 Animal Toxicology and/or Pharmacology

In a nonclinical study using intravenous administration of posaconazole in very young dogs (dosed from 2 to 8 weeks of age), an increase in the incidence of brain ventricle enlargement was observed in treated animals as compared with concurrent control animals. No difference in the incidence of brain ventricle enlargement between control and treated animals was observed following the subsequent 5-month treatment-free period. There were no neurologic, behavioral or developmental abnormalities in the dogs with this finding, and a similar brain finding was not seen with oral posaconazole administration to juvenile dogs (4 days to 9 months of age).

The clinical significance of this finding is unknown; therefore, the use of posaconazole injection to patients under 18 years of age is not recommended.

14 CLINICAL STUDIES

14.1 Prophylaxis of Aspergillus and Candida Infections with Posaconazole Oral Suspension

Two randomized, controlled studies were conducted using posaconazole as prophylaxis for the prevention of invasive fungal infections (IFIs) among patients at high risk due to severely compromised immune systems.

The first study (Oral Suspension Study 1) was a randomized, double-blind trial that compared posaconazole oral suspension (200 mg three times a day) with fluconazole capsules (400 mg once daily) as prophylaxis against invasive fungal infections in allogeneic hematopoietic stem cell transplant (HSCT) recipients with Graft versus Host Disease (GVHD). Efficacy of prophylaxis was evaluated using a composite endpoint of proven/probable IFIs, death, or treatment with systemic antifungal therapy (patients may have met more than one of these criteria). This assessed all patients while on study therapy plus 7 days and at 16 weeks post-randomization. The mean duration of therapy was comparable between the 2 treatment groups (80 days, posaconazole; 77 days, fluconazole). Table 24 contains the results from Oral Suspension Study 1.

Table 24: Results from Blinded Clinical Study in Prophylaxis of IFI in All Randomized Patients with Hematopoietic Stem Cell Transplant (HSCT) and Graft-vs.-Host Disease (GVHD): Oral Suspension Study 1
Posaconazolen=301 Fluconazolen=299
*
Patients may have met more than one criterion defining failure.
Use of systemic antifungal therapy (SAF) criterion is based on protocol definitions (empiric/IFI usage >4 consecutive days).
95% confidence interval (posaconazole-fluconazole) = (-11.5%, +3.7%).
§
Patients who are lost to follow-up (not observed for 112 days), and who did not meet another clinical failure endpoint. These patients were considered failures.
On therapy plus 7 days
Clinical Failure * 50 (17%) 55 (18%)
Failure due to:
Proven/Probable IFI 7 (2%) 22 (7%)
(Aspergillus) 3 (1%) 17 (6%)
(Candida) 1 (<1%) 3 (1%)
(Other) 3 (1%) 2 (1%)
All Deaths 22 (7%) 24 (8%)
Proven/probable fungal infection prior to death 2 (<1%) 6 (2%)
SAF 27 (9%) 25 (8%)
Through 16 weeks
Clinical Failure *, 99 (33%) 110 (37%)
Failure due to:
Proven/Probable IFI 16 (5%) 27 (9%)
(Aspergillus) 7 (2%) 21 (7%)
(Candida) 4 (1%) 4 (1%)
(Other) 5 (2%) 2 (1%)
All Deaths 58 (19%) 59 (20%)
Proven/probable fungal infection prior to death 10 (3%) 16 (5%)
SAF 26 (9%) 30 (10%)
Event free lost to follow-up § 24 (8%) 30 (10%)

The second study (Oral Suspension Study 2) was a randomized, open-label study that compared posaconazole oral suspension (200 mg 3 times a day) with fluconazole suspension (400 mg once daily) or itraconazole oral solution (200 mg twice a day) as prophylaxis against IFIs in neutropenic patients who were receiving cytotoxic chemotherapy for AML or MDS. As in Oral Suspension Study 1, efficacy of prophylaxis was evaluated using a composite endpoint of proven/probable IFIs, death, or treatment with systemic antifungal therapy (Patients might have met more than one of these criteria). This study assessed patients while on treatment plus 7 days and 100 days postrandomization. The mean duration of therapy was comparable between the 2 treatment groups (29 days, posaconazole; 25 days, fluconazole or itraconazole). Table 25 contains the results from Oral Suspension Study 2.

Table 25: Results from Open-Label Clinical Study 2 in Prophylaxis of IFI in All Randomized Patients with Hematologic Malignancy and Prolonged Neutropenia: Oral Suspension Study 2
Posaconazolen=304 Fluconazole/Itraconazolen=298
*
95% confidence interval (posaconazole-fluconazole/itraconazole) = (-22.9%, -7.8%).
Patients may have met more than one criterion defining failure.
Use of systemic antifungal therapy (SAF) criterion is based on protocol definitions (empiric/IFI usage >3 consecutive days).
§
Patients who are lost to follow-up (not observed for 100 days), and who did not meet another clinical failure endpoint. These patients were considered failures.
On therapy plus 7 days
Clinical Failure *, 82 (27%) 126 (42%)
Failure due to:
Proven/Probable IFI 7 (2%) 25 (8%)
(Aspergillus) 2 (1%) 20 (7%)
(Candida) 3 (1%) 2 (1%)
(Other) 2 (1%) 3 (1%)
All Deaths 17 (6%) 25 (8%)
Proven/probable fungal infection prior to death 1 (<1%) 2 (1%)
SAF 67 (22%) 98 (33%)
Through 100 days postrandomization
Clinical Failure 158 (52%) 191 (64%)
Failure due to:
Proven/Probable IFI 14 (5%) 33 (11%)
(Aspergillus) 2 (1%) 26 (9%)
(Candida) 10 (3%) 4 (1%)
(Other) 2 (1%) 3 (1%)
All Deaths 44 (14%) 64 (21%)
Proven/probable fungal infection prior to death 2 (1%) 16 (5%)
SAF 98 (32%) 125 (42%)
Event free lost to follow-up § 34 (11%) 24 (8%)

In summary, 2 clinical studies of prophylaxis were conducted with the posaconazole oral suspension. As seen in the accompanying tables (Tables 24 and 25), clinical failure represented a composite endpoint of breakthrough IFI, mortality and use of systemic antifungal therapy. In Oral Suspension Study 1 (Table 24), the clinical failure rate of posaconazole (33%) was similar to fluconazole (37%), (95% CI for the difference posaconazole–comparator -11.5% to 3.7%) while in Oral Suspension Study 2 (Table 25) clinical failure was lower for patients treated with posaconazole (27%) when compared to patients treated with fluconazole or itraconazole (42%), (95% CI for the difference posaconazole–comparator -22.9% to -7.8%).

All-cause mortality was similar at 16 weeks for both treatment arms in Oral Suspension Study 1 [POS 58/301 (19%) vs. FLU 59/299 (20%)]; all-cause mortality was lower at 100 days for posaconazole-treated patients in Oral Suspension Study 2 [POS 44/304 (14%) vs. FLU/ITZ 64/298 (21%)]. Both studies demonstrated substantially fewer breakthrough infections caused by Aspergillus species in patients receiving posaconazole prophylaxis when compared to patients receiving fluconazole or itraconazole.

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