Nizoral (Ketoconazole) - Description and Clinical Pharmacology

DESCRIPTION

NIZORAL^® (ketoconazole) is a synthetic broad-spectrum antifungal agent available in scored white tablets, each containing 200 mg ketoconazole base for oral administration. Inactive ingredients are colloidal silicon dioxide, corn starch, lactose, magnesium stearate, microcrystalline cellulose, and povidone. Ketoconazole is cis -1- acetyl-4-[4-[[2-(2,4-dichlorophenyl)-2-(1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl]methoxyl]phenyl] piperazine and has the following structural formula:

Ketoconazole is a white to slightly beige, odorless powder, soluble in acids, with a molecular weight of 531.44.

CLINICAL PHARMACOLOGY

Mean peak plasma levels of approximately 3.5 µg/mL are reached within 1 to 2 hours, following oral administration of a single 200 mg dose taken with a meal. Subsequent plasma elimination is biphasic with a half-life of 2 hours during the first 10 hours and 8 hours thereafter. Following absorption from the gastrointestinal tract, NIZORAL^® (ketoconazole) is converted into several inactive metabolites. The major identified metabolic pathways are oxidation and degradation of the imidazole and piperazine rings, oxidative O-dealkylation and aromatic hydroxylation. About 13% of the dose is excreted in the urine, of which 2 to 4% is unchanged drug. The major route of excretion is through the bile into the intestinal tract. In vitro, the plasma protein binding is about 99% mainly to the albumin fraction. Only a negligible proportion of ketoconazole reaches the cerebral-spinal fluid. Ketoconazole is a weak dibasic agent and thus requires acidity for dissolution and absorption.

NIZORAL^® Tablets are active against clinical infections with Blastomyces dermatitidis, Candida spp., Coccidioides immitis, Histoplasma capsulatum, Paracoccidioides brasiliensis, and Phialophora spp. NIZORAL^® Tablets are also active against Trichophyton spp., Epidermophyton spp., and Microsporum spp. Ketoconazole is also active in vitro against a variety of fungi and yeast. In animal models, activity has been demonstrated against Candida spp., Blastomyces dermatitidis, Histoplasma capsulatum, Malassezia furfur, Coccidioides immitis, and Cryptococcus neoformans.

Mode of Action

In vitro studies suggest that ketoconazole impairs the synthesis of ergosterol, which is a vital component of fungal cell membranes.