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 are approximately 3.3 times higher than those obtained by HPLC due to the presence of the bioactive metabolite, hydroxyitraconazole. (See MICROBIOLOGY.)
The pharmacokinetics of itraconazole after intravenous administration and its absolute oral bioavailability from an oral solution were studied in a randomized crossover study in 6 healthy male volunteers. The observed absolute oral bioavailability of itraconazole was 55%.
The oral bioavailability of itraconazole is maximal when SPORANOX® (itraconazole) Capsules are taken with a full meal. The pharmacokinetics of itraconazole were studied in 6 healthy male volunteers who received, in a crossover design, single 100-mg doses of itraconazole as a polyethylene glycol capsule, with or without a full meal. The same 6 volunteers also received 50 mg or 200 mg with a full meal in a crossover design. In this study, only itraconazole plasma concentrations were measured. The respective pharmacokinetic parameters for itraconazole are presented in the table below:
| 50 mg
(fed) | 100 mg
(fed) | 100 mg
(fasted) | 200 mg
(fed) |
|---|
Cmax
(ng/mL) | 45 ± 16mean± standard deviation | 132 ± 67 | 38 ± 20 | 289 ± 100 |
Tmax
(hours) | 3.2 ± 1.3 | 4.0 ± 1.1 | 3.3 ± 1.0 | 4.7 ± 1.4 |
AUC0-∞
(ng·h/mL) | 567 ± 264 | 1899 ± 838 | 722 ± 289 | 5211 ± 2116 |
Doubling the SPORANOX® dose results in approximately a three-fold increase in the itraconazole plasma concentrations.
Values given in the table below represent data from a crossover pharmacokinetics study in which 27 healthy male volunteers each took a single 200-mg dose of SPORANOX® Capsules with or without a full meal:
| Itraconazole | Hydroxyitraconazole |
|---|
| Fed | Fasted | Fed | Fasted |
|---|
Cmax
(ng/mL) | 239 ± 85mean± standard deviation | 140 ± 65 | 397 ± 103 | 286 ± 101 |
Tmax
(hours) | 4.5 ± 1.1 | 3.9 ± 1.0 | 5.1 ± 1.6 | 4.5 ± 1.1 |
| AUC0-∞ (ng·h/mL) | 3423 ± 1154 | 2094 ± 905 | 7978 ± 2648 | 5191 ± 2489 |
| t1/2 (hours) | 21 ± 5 | 21 ± 7 | 12 ± 3 | 12 ± 3 |
Absorption of itraconazole under fasted conditions in individuals with relative or absolute achlorhydria, such as patients with AIDS or volunteers taking gastric acid secretion suppressors (e.g., H2 receptor antagonists), was increased when SPORANOX® Capsules were administered with a cola beverage. Eighteen men with AIDS received single 200-mg doses of SPORANOX® Capsules under fasted conditions with 8 ounces of water or 8 ounces of a cola beverage in a crossover design. The absorption of itraconazole was increased when SPORANOX® Capsules were coadministered with a cola beverage, with AUC0-24 and Cmax increasing 75% ± 121% and 95% ± 128%, respectively.
Thirty healthy men received single 200-mg doses of SPORANOX® Capsules under fasted conditions either 1) with water; 2) with water, after ranitidine 150 mg b.i.d. for 3 days; or 3) with cola, after ranitidine 150 mg b.i.d. for 3 days. When SPORANOX® Capsules were administered after ranitidine pretreatment, itraconazole was absorbed to a lesser extent than when SPORANOX® Capsules were administered alone, with decreases in AUC0-24 and Cmax of 39% ± 37% and 42% ± 39%, respectively. When SPORANOX® Capsules were administered with cola after ranitidine pretreatment, itraconazole absorption was comparable to that observed when SPORANOX® Capsules were administered alone. (See PRECAUTIONS: Drug Interactions.)
Steady-state concentrations were reached within 15 days following oral doses of 50 mg to 400 mg daily. Values given in the table below are data at steady-state from a pharmacokinetics study in which 27 healthy male volunteers took 200-mg SPORANOX® Capsules b.i.d.(with a full meal) for 15 days:
| Itraconazole | Hydroxyitraconazole |
|---|
| Cmax (ng/mL) | 2282 ± 514mean ± standard deviation | 3488 ± 742 |
| Cmin (ng/mL) | 1855 ± 535 | 3349 ± 761 |
| Tmax (hours) | 4.6 ± 1.8 | 3.4 ± 3.4 |
| AUC0-12 h (ng·h/mL) | 22569 ± 5375 | 38572 ± 8450 |
| t1/2 (hours) | 64 ± 32 | 56 ± 24 |
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 liters.
Itraconazole is metabolized predominately by the cytochrome P450 3A4 isoenzyme system (CYP3A4), resulting in the formation of several metabolites, including hydroxyitraconazole, the major metabolite. Results of a pharmacokinetics study suggest that itraconazole may undergo saturable metabolism with multiple dosing. Fecal excretion of the parent drug varies between 3-18% of the dose. Renal excretion of the parent drug is less than 0.03% of the dose. About 40% of the dose is excreted as inactive metabolites in the urine. No single excreted metabolite represents more than 5% of a dose. Itraconazole total plasma clearance averaged 381 ± 95 mL/minute following intravenous administration. (See CONTRAINDICATIONS and PRECAUTIONS: Drug Interactions for more information.)
Special Populations:
Renal Insufficiency:
A pharmacokinetic study using a single 200-mg dose of itraconazole (four 50-mg capsules) was conducted in three groups of patients with renal impairment (uremia: n=7; hemodialysis: n=7; and continuous ambulatory peritoneal dialysis: n=5). In uremic subjects with a mean creatinine clearance of 13 mL/min. × 1.73 m2, the bioavailability was slightly reduced compared with normal population parameters. This study did not demonstrate any significant effect of hemodialysis or continuous ambulatory peritoneal dialysis on the pharmacokinetics of itraconazole (Tmax, Cmax, and AUC0-8). Plasma concentration-versus-time profiles showed wide intersubject variation in all three groups.
Hepatic Insufficiency:
A pharmacokinetic study using a single 100-mg dose of itraconazole (one 100-mg capsule) was conducted in 6 healthy and 12 cirrhotic subjects. No statistically significant differences in AUC were seen between these two groups. A statistically significant reduction in mean Cmax (47%) and a twofold increase in the elimination half-life (37 ± 17 hours) of itraconazole were noted in cirrhotic subjects compared with healthy subjects. Patients with impaired hepatic function should be carefully monitored when taking itraconazole. The prolonged elimination half-life of itraconazole observed in cirrhotic patients should be considered when deciding to initiate therapy with other medications metabolized by CYP3A4. (See BOX WARNING, CONTRAINDICATIONS, PRECAUTIONS: Drug Interactions)
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® 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® Capsules, SPORANOX® should be discontinued. (See CONTRAINDICATIONS, 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. The bioactive metabolite, hydroxyitraconazole, has not been evaluated against Histoplasma capsulatum and Blastomyces dermatitidis. 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.
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.
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