CLINICAL PHARMACOLOGY
Pharmacokinetics and Metabolism
NOTE: The plasma concentrations reported below were measured by high-performance
liquid chromatography (HPLC) specific for itraconazole. When itraconazole in
plasma is measured by a bioassay, values reported may be higher than those obtained
by HPLC due to the presence of the bioactive metabolite, hydroxyitraconazole.
(See Microbiology.)
The pharmacokinetics of SPORANOX® (itraconazole) Injection
(200 mg b.i.d. for two days, then 200 mg q.d. for five days) followed by oral
dosing of SPORANOX® (itraconazole injection) Capsules were studied in patients with advanced HIV
infection. Steady-state plasma concentrations were reached after the fourth
dose for itraconazole and by the seventh dose for hydroxyitraconazole.
Steady-state plasma concentrations were maintained by administration of
SPORANOX® Capsules, 200 mg b.i.d. Pharmacokinetic parameters for itraconazole
and hydroxyitraconazole are presented in the table below:
Parameter |
Injection
Day 7
n=29 |
Capsule, 200 mg b.i.d.
Day 36
n=12 |
itraconazole |
hydroxyitraconazole |
itraconazole |
hydroxyitraconazole |
Cmax (ng/mL) |
2856 ± 866* |
1906 ± 612 |
2010 ± 1420 |
2614 ± 1703 |
tmax (hr) |
1.08 ± 0.14 |
8.53 ± 6.36 |
3.92 ± 1.83 |
5.92 ± 6.14 |
AUC0-12h (ng•h/mL) |
-- |
- |
18768 ± 13933 |
28516 ± 19149 |
AUC0-24h (ng•h/mL) |
30605 ± 8961 |
42445 ± 13282 |
-- |
- |
* mean ± standard deviation |
The estimated mean ±SD half-life at steady-state of
itraconazole after intravenous infusion was 35.4 ± 29.4 hours. In previous
studies, the mean elimination half-life for itraconazole at steady-state after
daily oral administration of 100 to 400 mg was 30-40 hours.
The plasma protein binding of itraconazole is 99.8% and that
of hydroxyitraconazole is 99.5%. Following intravenous administration, the
volume of distribution of itraconazole averaged 796 ± 185 L.
Each intravenous dose of 200 mg itraconazole contains 8g hydroxypropyl-βcyclodextrin
to increase the solubility of itraconazole. The pharmacokinetic profiles of
each are described below. (See Special Populations-Renal Insufficiency.)
Itraconazole is metabolized predominately by the cytochrome P450 3A4 isoenzyme
system (CYP3A4), resulting in the formation of several metabolites. Hydroxyitraconazole,
the major metabolite, has in vitro antifungal activity comparable to itraconazole.
Results of a pharmacokinetics study suggest that itraconazole may undergo saturable
metabolism with multiple dosing. Based on an oral dose, fecal excretion of the
parent drug varies between 3-18% of the dose. Renal excretion of itraconazole
and the active metabolite hydroxyitraconazole account for less than 1% of an
intravenous dose. Itraconazole is excreted mainly as inactive metabolites in
urine (35%) and feces (54%) within one week of an oral dose. No single excreted
metabolite represents more than 5% of a dose. Itraconazole mean total plasma
clearance is 278 ± 79 mL/min following intravenous administration. A
mean of 89.2% of the administered intravenous dose of hydroxypropyl-β-cyclodextrin
is excreted in urine. (See CONTRAINDICATIONS
and PRECAUTIONS: DRUG INTERACTIONS
for more information.)
Special Populations
Renal Insufficiency
A small fraction ( < 1%) of an intravenous dose of
itraconazole is excreted unchanged in urine.
After a single intravenous dose, the mean terminal
half-lives of itraconazole in patients with mild (CrCl 50-79 mL/min), moderate
(CrCl 20-49 mL/min), and severe renal impairment (CrCl < 20 mL/min) were
similar to that in healthy subjects (range of means 42-49 hr vs 48 hr in
renally impaired patients and healthy subjects, respectively). Overall exposure
to itraconazole, based on AUC, was decreased in patients with moderate and
severe renal impairment by approximately 30% and 40%, respectively, as compared
with subjects with normal renal function.
Data are not available in renally impaired patients during long-term use of
itraconazole. Dialysis has no effect on the half-life or clearance of itraconazole
or hydroxyitraconazole. (See CONTRAINDICATIONS,
PRECAUTIONS and DOSAGE
AND ADMINISTRATION.)
In patients with normal renal function, the pharmacokinetic
profile of hydroxypropylβ-cyclodextrin, an ingredient of SPORANOX® (itraconazole injection)
intravenous formulation, has a short half-life of 1 to 2 hours, and
demonstrates no accumulation following successive daily doses. In healthy
subjects and in patients with mild to severe renal insufficiency, the majority
of an 8 g dose of hydroxypropyl-β-cyclodextrin (per 200 mg itraconazole)
is eliminated in the urine. Following a single intravenous dose of itraconazole
200 mg, clearance of hydroxypropyl-β-cyclodextrin was reduced in subjects
with mild, moderate, and severe renal impairment, resulting in higher exposure
to hydroxypropyl-β-cyclodextrin; in these subjects, half-life values were
increased over normal values by approximately two-, four-, and six-fold,
respectively. In these patients, successive infusions may result in
accumulation of hydroxypropyl-β-cyclodextrin until steady state is
reached. Hydroxypropyl-β-cyclodextrin is removed by hemodialysis.
In patients with mild (defined as creatinine clearance 50-80 mL/min) and moderate
(defined as creatinine clearance 30-49 mL/min) renal impairment, SPORANOX® (itraconazole injection)
Injection should be used with caution. Serum creatinine levels should be closely
monitored and, if renal toxicity is suspected, consideration should be given
to modifying the antifungal regimen to an alternate medication with similar
antimycotic coverage. SPORANOX® (itraconazole injection) Injection is contraindicated in patients
with severe renal impairment (creatinine clearance < 30 mL/min). (See CONTRAINDICATIONS,
PRECAUTIONS, and DOSAGE
AND ADMINISTRATION.)
Hepatic Insufficiency
Studies have not been conducted with intravenous itraconazole in patients with
hepatic impairment. Itraconazole is predominantly metabolized in the liver.
Patients with impaired hepatic function should be carefully monitored when taking
itraconazole. A pharmacokinetic study using a single oral 100-mg dose of itraconazole
(one 100-mg capsule) was conducted in 6 healthy and 12 cirrhotic subjects. A
statistically significant reduction in mean Cmax (47%) and a twofold increase
in the elimination half-life (37 ± 17 hours vs. 16 ± 5 hours)
of itraconazole were noted in cirrhotic subjects compared with healthy subjects.
However, overall exposure to itraconazole based on AUC, was similar in cirrhotic
patients and in healthy subjects. The prolonged elimination half-life of itraconazole
observed in the single oral dose clinical trial with itraconazole capsules in
cirrhotic patients should be considered when deciding to initiate therapy with
other medications metabolized by CYP3A4. Data are not available in cirrhotic
patients during long-term use of itraconazole. (See BOX
WARNING, CONTRAINDICATIONS, PRECAUTIONS:
DRUG INTERACTIONS and DOSAGE
AND ADMINISTRATION.)
Decreased Cardiac Contractility
When itraconazole was administered intravenously to anesthetized dogs, a dose-related
negative inotropic effect was documented. In a healthy volunteer study of SPORANOX® (itraconazole injection)
Injection (intravenous infusion), transient, asymptomatic decreases in left
ventricular ejection fraction were observed using gated SPECT imaging; these
resolved before the next infusion, 12 hours later. If signs or symptoms of congestive
heart failure appear during administration of SPORANOX® (itraconazole injection) Injection, monitor
carefully and consider other treatment alternatives which may include discontinuation
of SPORANOX® Injection administration. (See WARNINGS,
PRECAUTIONS: DRUG INTERACTIONS and
ADVERSE REACTIONS: Post-marketing Experience
for more information.)
Microbiology
Mechanism of Action
In vitro studies have demonstrated that itraconazole
inhibits the cytochrome P450-dependent synthesis of ergosterol, which is a
vital component of fungal cell membranes.
Activity In Vitro and In Vivo
Itraconazole exhibits in vitro activity against Blastomyces
dermatitidis, Histoplasma capsulatum, Histoplasma duboisii, Aspergillus flavus,
Aspergillus fumigatus, Candida albicans, and Cryptococcus neoformans.
Itraconazole also exhibits varying in vitro activity against Sporothrix
schenckii, Trichophyton species, Candida krusei, and other Candida
species.
Candida krusei, Candida glabrata and Candida
tropicalis are generally the least susceptible Candida species, with
some isolates showing unequivocal resistance to itraconazole in vitro.
Itraconazole is not active against Zygomycetes (e.g., Rhizopus
spp., Rhizomucor spp., Mucor spp. and Absidia spp.), Fusarium
spp., Scedosporium spp. and Scopulariopsis spp.
The bioactive metabolite, hydroxyitraconazole, has not been
evaluated against Histoplasma capsulatum, Blastomyces dermatitidis,
Zygomycete, Fusarium spp., Scedosporium spp. and Scopulariopsis
spp. Correlation between minimum inhibitory concentration (MIC) results in
vitro and clinical outcome has yet to be established for azole antifungal
agents.
Itraconazole administered orally was active in a variety of
animal models of fungal infection using standard laboratory strains of fungi.
Fungistatic activity has been demonstrated against disseminated fungal
infections caused by Blastomyces dermatitidis, Histoplasma duboisii,
Aspergillus fumigatus, Coccidioides immitis, Cryptococcus neoformans,
Paracoccidioides brasiliensis, Sporothrix schenckii, Trichophyton rubrum, and
Trichophyton mentagrophytes.
Itraconazole administered at 2.5 mg/kg and 5 mg/kg via the
oral and parenteral routes increased survival rates and sterilized organ
systems in normal and immunosuppressed guinea pigs with disseminated Aspergillus
fumigatus infections. Oral itraconazole administered daily at 40 mg/kg and
80 mg/kg increased survival rates in normal rabbits with disseminated disease
and in immunosuppressed rats with pulmonary Aspergillus fumigatus infection,
respectively. Itraconazole has demonstrated antifungal activity in a variety of
animal models infected with Candida albicans and other Candida
species.
Resistance
Isolates from several fungal species with decreased
susceptibility to itraconazole have been isolated in vitro and from
patients receiving prolonged therapy.
Several in vitro studies have reported that some
fungal clinical isolates, including Candida species, with reduced
susceptibility to one azole antifungal agent may also be less susceptible to
other azole derivatives. The finding of cross-resistance is dependent on a
number of factors, including the species evaluated, its clinical history, the
particular azole compounds compared, and the type of susceptibility test that
is performed. The relevance of these in vitro susceptibility data to
clinical outcome remains to be elucidated.
Candida krusei, Candida glabrata and Candida
tropicalis are generally the least susceptible Candida species, with
some isolates showing unequivocal resistance to itraconazole in vitro.
Itraconazole is not active against Zygomycetes (e.g.,
Rhizopus spp., Rhizomucor spp., Mucor spp. and Absidia
spp.), Fusarium spp., Scedosporium spp. and Scopulariopsis
spp.
Studies (both in vitro and in vivo) suggest
that the activity of amphotericin B may be suppressed by prior azole antifungal
therapy. As with other azoles, itraconazole inhibits the 14C-demethylation step
in the synthesis of ergosterol, a cell wall component of fungi. Ergosterol is
the active site for amphotericin B. In one study the antifungal activity of
amphotericin B against Aspergillus fumigatus infections in mice was
inhibited by ketoconazole therapy. The clinical significance of test results
obtained in this study is unknown.
Clinical Studies
Empiric Therapy in Febrile Neutropenic Patients
An open randomized trial compared the efficacy and safety of
itraconazole (intravenous followed by oral solution) with amphotericin B for
empiric therapy in 384 febrile, neutropenic patients with hematologic
malignancies who had suspected fungal infections. Patients received either
itraconazole (injection, 200 mg b.i.d. for 2 days followed by 200 mg once daily
for up to 14 days, followed by oral solution, 200 mg b.i.d.) or amphotericin B
(total daily dose of 0.7-1.0 mg/kg body weight). The longest treatment duration
was 28 days. An outcome assignment of “success” required (a) patient
survival with resolution of fever and neutropenia within 28 days of treatment,
(b) absence of emergent fungal infections, (c) no discontinuation of therapy
due to toxicity or lack of efficacy, and (d) treatment for three or more days.
The success rate using an intent-to-treat analysis was 47% for the itraconazole
group and 38% for the amphotericin B arm.
Overview of Efficacy (Intent-to-Treat Population)
Efficacy Parameters |
SPORANOX®
N=179 (%) |
Amphotericin B
N=181 (%) |
Success |
Unevaluable* |
84 (47%) |
68 (38%) |
Failure |
24 (13%) |
44 (24%) |
Reason for Failure |
71 (40%) |
69 (38%) |
Intolerance after > 3 days of antifungal medication |
12 |
37 |
Persistent fever |
20 |
7 |
Change in antifungal medication due to fever |
13 |
1 |
Emergent fungal infection |
10 |
9 |
Documented bacterial or viral infection |
7 |
8 |
Insufficient response |
6 |
5 |
Deterioration of signs and symptoms |
2 |
0 |
Death after > 3 days antifungal medication |
1 |
2 |
Resolution of fever |
131 (73%) |
127 (70%) |
Survival |
161 (90%) |
156 (86%) |
* Treatment duration ≤ 3 days (including patients who died within 3 days, withdrew because of adverse events or were deemed ineligible due to a confirmed pre-treatment infection). |