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Chapter: Modern Pharmacology with Clinical Applications: Antifungal Drugs

Itraconazole Antifungal Drug

Absorption, Distribution, Metabolism, and Excretion



Absorption, Distribution, Metabolism, and Excretion


Although itraconazole and fluconazole are both tria-zoles, they are chemically and pharmacologically dis-tinct. Itraconazole (Sporanox) is lipophilic and water in-soluble and requires a low gastric pH for absorption. Oral bioavailability is variable, only 50 to 60% when taken with food and 20% or less when the drug is taken on an empty stomach. Itraconazole is highly protein bound (99%) and is metabolized in the liver and ex-creted into the bile. With initial dosing, the plasma half-life is 15 to 20 hours; steady-state serum concentrations are reached only after 2 weeks of therapy, when the half-life is extended to 30 to 35 hours. In lipophilic tis-sues, drug concentration is 2 to 20 times that found in

serum. Drug does not appear in significant quantities in the urine and cannot be measured in spinal fluid.


Clinical Uses


Itraconazole is most useful in the long-term suppressive treatment of disseminated histoplasmosis in AIDS and in the oral treatment of nonmeningeal, non–life-threat-ening blastomycosis. It appears to be the drug of choice for all forms of sporotrichosis except meningitis and may have a lower relapse rate in the treatment of dis-seminated coccidioidomycosis than does fluconazole.


Itraconazole has replaced ketoconazole as the drug of choice in the treatment of paracoccidioidomycosis and chromomycosis, based on its lower toxicity profile. Efficacy has also been reported in the treatment of in-vasive aspergillosis.


Despite negligible cerebrospinal fluid concentra-tions, itraconazole shows promise in the treatment of cryptococcal and coccidioidal meningitis. Additional uses for itraconazole include treatment of vaginal can-didiasis, tinea versicolor, dermatophyte infections, and onychomycosis. Fungal nail infections account for most use of this drug in the outpatient setting.

Adverse Effects


Itraconazole is usually well tolerated but can be associ-ated with nausea and epigastric distress. Dizziness and headache also have been reported. High doses may cause hypokalemia, hypertension, and edema. Itraconazole, un-like ketoconazole, is not associated with hormonal sup-pression. Hepatotoxicity occurs in fewer than 5% of cases and is usually manifested by reversible liver en-zyme elevations.


Drug Interactions


Itraconazole has significant interactions with a number of commonly prescribed drugs, such as rifampin, phe-nytoin, and carbamazepine. Itraconazole raises serum digoxin and cyclosporine levels and may affect the me-tabolism of oral hypoglycemic agents and coumadin. Absorption of itraconazole is impaired by antacids, H2 blockers, proton pump inhibitors, and drugs that contain buffers, such as the antiretroviral agent didanosine.


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