Ketoconazole

Absorption

Ketoconazole requires an acidic environment to become soluble in water. At pH values above 3 it becomes increasingly insoluble with about 10% entering solution in 1 h. At pH less than 3 dissolution is 85% complete in 5 min and entirely complete within 30 min. A single 200 mg oral dose produces a Cmax of 2.5-3 mcg/mL with a Tmax of 1-4 h. Administering ketoconazole with food consistently increases Cmax and delays Tmax but literature is contradictory regarding the effect on AUC, which may experience a small decrease. A bioavailablity of 76% has been reported for ketoconazole.

Toxicity

Symptoms of overdose include acute liver injury, which may include both hepatocellular and cholestatic injury, accompanied by anorexia, fatigue, nausea, and jaundice. In case of overdose, gastric lavage with activated charcoal may be used if within one hour of ketoconazole ingestion otherwise provide supportive care. If the patient shows signs of adrenal insufficiency, administer 100 mg hydrocortisone once together with saline and glucose infusion and monitor the patient closely. Blood pressure and fluid and electrolyte balance should be monitored over the next few days.

Description

Ketoconazole (Nizoral), an orally effective broadspectrum antifungal agent, blocks hydroxylating enzyme systems by interacting with cytochrome P450 at the heme iron site to inhibit steroid and/or androgen synthesis in adrenals, gonads, liver, and kidney. The most sensitive site of action appears to be the C17-20 lyase reaction involved in the formation of sex steroids. This explains the greater suppressibility of testosterone production than with cortisol. Cholesterol side-chain cleavage and 11β/18-hydroxylase are secondary sites of inhibition.

The Uses of Ketoconazole

Ketoconazole is used to treat candidiasis, chronic mucocutaneous candidiasis, oral thrush, candiduria, blastomycosis, coccidioidomycosis, histoplasmosis, chromomycosis, and paracoccidioidomycosis. Ketoconazole is an antifungal agent.

Indications

Ketoconazole is used to treat serious fungal or yeast infections, such as candidiasis (thrush, oral thrush), blastomycosis (Gilchrist's disease), coccidioidomycosis (Valley fever, San Joaquin Valley fever), histoplasmosis (Darling's disease), chromoblastomycosis (chromomycosis), or paracoccidioidomycosis (South American blastomycosis, Lutz-Splendore-Almeida disease). This medicine works by killing the fungus or yeast or preventing its growth.

Background

Ketoconazole is an imidazole antifungal agent used in the prevention and treatment of a variety of fungal infections. It functions by preventing the synthesis of ergosterol, the fungal equivalent of cholesterol, thereby increasing membrane fluidity and preventing growth of the fungus. Ketoconazole was first approved in an oral formulation for systemic use by the FDA in 1981. At this time it was considered a significant improvement over previous antifungals, miconazole and clotrimazole, due to its broad spectrum and good absorption. However, it was discovered that ketoconazole produces frequent gastrointestinal side effects and dose-related hepatitis. These effects combined with waning efficacy led to its eventual replacement by triazole agents, fluconazole, itraconazole, voriconazole, and posaconazole. Ketoconazole and its predecessor clotrimazole continue to be used in topical formulations.

What are the applications of Application

Ketoconazole is an inhibitor of CYP proteins, thromboxane synthetase, and 5-LO

Regulations

Due to its hepatotoxic side effects, oral ketoconazole was withdrawn from the European and Australian markets in 2013. The United States imposed strict relabeling requirements and restrictions for prescription, with Canada issuing a risk communication echoing these concerns. Today, oral ketoconazole is only indicated for endemic mycoses, where alternatives are not available or feasible. Meanwhile, topical ketoconazole is effective, safe, and widely prescribed for superficial mycoses, particularly as the first-line treatment for tinea versicolor.

Metabolism

The major metabolite of ketoconazole appears to be M2, an end product resulting from oxidation of the imidazole moiety. CYP3A4 is known to be the primary contributor to this reaction with some contribution from CYP2D6. Other metabolites resulting from CYP3A4 mediated oxidation of the imidazole moiety include M3, M4, and M5. Ketoconazole may also undergo N-deacetylation to M14, , alkyl oxidation to M7, N-oxidation to M13, or aromatic hydroxylation to M8, or hydroxylation to M9. M9 may further undergo oxidation of the hydroxyl to form M12, N-dealkylation to form M10 with a subsequent N-dealkylation to M15, or may form an iminium ion. No metabolites are known to be active however oxidation metabolites of M14 have been implicated in cytotoxicity.