Ketoconazole

Ketoconazole, sold under the brand name Nizoral, among others, is an antiandrogen, antifungal, and antiglucocorticoid medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin infections such as tinea, cutaneous candidiasis, pityriasis versicolor, dandruff, and seborrheic dermatitis. Taken by mouth it is a less preferred option and recommended for only severe infections when other agents cannot be used. Other uses include treatment of excessive male-patterned hair growth in women and Cushing's syndrome.

Common side effects when applied to the skin include redness. Common side effects when taken by mouth include nausea, headache, and liver problems. Liver problems may result in death or the need for a liver transplantation. Other severe side effects when taken orally include QT prolongation, adrenocortical insufficiency, and anaphylaxis. It is an imidazole and works by hindering the production of ergosterol required for the fungal cell membrane, thereby slowing growth.

Ketoconazole was patented in 1977 by Belgian pharmaceutical company Janssen, and came into medical use in 1981. It is available as a generic medication and formulations that are applied to the skin are over the counter in the United Kingdom. In 2022, it was the 175th most commonly prescribed medication in the United States, with more than 2million prescriptions. The formulation that is taken by mouth was withdrawn in the European Union and in Australia in 2013, and in China in 2015. In addition, its use was restricted in the United States and Canada in 2013.

Medical uses

Topical antifungal

Topically administered ketoconazole is usually prescribed for fungal infections of the skin and mucous membranes, such as athlete's foot, ringworm, candidiasis (yeast infection or thrush), jock itch, and tinea versicolor. Topical ketoconazole is also used as a treatment for dandruff (seborrheic dermatitis of the scalp) and for seborrheic dermatitis on other areas of the body, perhaps acting in these conditions by suppressing levels of the fungus '' Malassezia furfur'' on the skin.

Systemic antifungal

Ketoconazole has activity against many kinds of fungi that may cause human disease, such as '' Candida'', '' Histoplasma'', '' Coccidioides'', and '' Blastomyces'' (although it is not active against '' Aspergillus''), chromomycosis and paracoccidioidomycosis. First made in 1977, ketoconazole was the first orally-active azole antifungal medication. However, ketoconazole has largely been replaced as a first-line systemic antifungal medication by other azole antifungal agents, such as fluconazole and/or itraconazole, because of ketoconazole's greater toxicity, poorer absorption, and more limited spectrum of activity.

Ketoconazole is used orally in dosages of 200 to 400 mg per day in the treatment of superficial and deep fungal infections.

Off-label uses

Hair loss

Ketoconazole shampoo in conjunction with an oral 5α-reductase inhibitor such as finasteride or dutasteride has been used off label to treat androgenic alopecia. It was speculated that antifungal properties of ketoconazole reduce scalp microflora and consequently may reduce follicular inflammation that contributes to alopecia.

Limited clinical studies suggest ketoconazole shampoo used either alone or in combination with other treatments may be useful in reducing hair loss in some cases.

Hormonal

The side effects of ketoconazole are sometimes harnessed in the treatment of non-fungal conditions. While ketoconazole blocks the synthesis of the sterol ergosterol in fungi, in humans, at high dosages (>800 mg/day), it potently inhibits the activity of several enzymes necessary for the conversion of cholesterol to steroid hormones such as testosterone and cortisol. Specifically, ketoconazole has been shown to inhibit cholesterol side-chain cleavage enzyme, which converts cholesterol to pregnenolone, 17α-hydroxylase and 17,20-lyase, which convert pregnenolone into androgens, and 11β-hydroxylase, which converts 11-deoxycortisol to cortisol. All of these enzymes are mitochondrial cytochrome p450 enzymes. Based on these antiandrogen and antiglucocorticoid effects, ketoconazole has been used with some success as a second-line treatment for certain forms of advanced prostate cancer and for the suppression of glucocorticoid synthesis in the treatment of Cushing's syndrome. However, in the treatment of prostate cancer, concomitant glucocorticoid administration is needed to prevent adrenal insufficiency. Ketoconazole has additionally been used, in lower dosages, to treat hirsutism and, in combination with a GnRH analogue, male-limited precocious puberty. In any case, the risk of hepatotoxicity with ketoconazole limits its use in all of these indications, especially in those that are benign such as hirsutism.

Ketoconazole has been used to prevent the testosterone flare at the initiation of GnRH agonist therapy in men with prostate cancer.

Contraindications

Oral ketoconazole has various contraindications, such as concomitant use with certain other drugs due to known drug interactions. Other contraindications of oral ketoconazole include liver disease, adrenal insufficiency, and known hypersensitivity to oral ketoconazole.

Side effects

Gastrointestinal

Vomiting, diarrhea, nausea, constipation, abdominal pain, upper abdominal pain, dry mouth, dysgeusia, dyspepsia, flatulence, tongue discoloration may occur.

Endocrine

The drug may cause adrenal insufficiency so the level of the adrenocortical hormones should be monitored while taking it. Oral ketoconazole at a dosage range of 400 to 2,000 mg/day has been found to result in a rate of gynecomastia of 21%.

Liver

In July 2013, the US Food and Drug Administration (FDA) issued a warning that taking ketoconazole by mouth can cause severe liver injuries and adrenal gland problems: adrenal insufficiency and worsening of other diseases related to the gland conditions. It recommends oral tablets should not be a first-line treatment for any fungal infection. It should be used for the treatment of certain fungal infections, known as endemic mycoses, only when alternative antifungal therapies are not available or not tolerated. As contraindication it should not be used in people with acute or chronic liver disease.

Hypersensitivity

Anaphylaxis after the first dose may occur. Other cases of hypersensitivity include urticaria.

Topical formulations

The topical formulations have not been associated with liver damage, adrenal problems, or drug interactions. These formulations include creams, shampoos, foams, and gels applied to the skin, unlike the ketoconazole tablets, which are taken by mouth.

Pregnancy

Ketoconazole is categorized as pregnancy category C(Risk not ruled out) in the US. Research in animals has shown it to cause teratogenesis when administered in high doses. A subsequent trial in Europe failed to show a risk to infants of mothers receiving ketoconazole.

Overdose

In the event of an overdose of oral ketoconazole, treatment should be supportive and based on symptoms. Activated charcoal may be administered within the first hour following overdose of oral ketoconazole.

Interactions

The concomitant use of the following medications are contraindicated with ketoconazole tablets:
* methadone, disopyramide, dronedarone
* irinotecan, lurasidone, colchicine
* alprazolam, oral midazolam, oral triazolam
* felodipine, ranolazine, tolvaptan, eplerenone
* HMG-CoA reductase inhibitors: lovastatin, simvastatin
* ergot alkaloids: ergotamine, dihydroergotamine, ergometrine, methylergometrine
* Others: cisapride, nisoldipine, dofetilide, pimozide

The following medications are not recommended with ketoconazole:
* carbamazepine, phenytoin
* gastric acid suppressants: antacids, antimuscarinics, histamine H₂ blockers, proton pump inhibitors
* sucralfate
* rifampin, rifabutin, isoniazid
* efavirenz, nevirapine

Ritonavir(an antiretrovial medication), is known for increasing the activity of ketoconazole. So it is recommended to reduce dosage.

There is also a list of drugs which significantly decrease systemic exposure to the ketoconazole and drugs whose systemic exposure is increased by the ketoconazole.

Pharmacology

Pharmacodynamics

Antifungal activity

As an antifungal, ketoconazole is structurally similar to imidazole, and interferes with the fungal synthesis of ergosterol, a constituent of fungal cell membranes, as well as certain enzymes. As with all azole antifungal agents, ketoconazole works principally by inhibiting the enzyme cytochrome P450 14α-demethylase (CYP51A1). This enzyme participates in the sterol biosynthesis pathway that leads from lanosterol to ergosterol. Lower doses of fluconazole and itraconazole are required to kill fungi compared to ketoconazole, as they have been found to have a greater affinity for fungal cell membranes.

Resistance to ketoconazole has been observed in a number of clinical fungal isolates, including ''Candida albicans''. Experimentally, resistance usually arises as a result of mutations in the sterol biosynthesis pathway. Defects in the sterol 5-6 desaturase enzyme reduce the toxic effects of azole inhibition of the 14-alpha demethylation step. Multidrug-resistance (MDR) genes can also play a role in reducing cellular levels of the drug. As azole antifungals all act at the same point in the sterol pathway, resistant isolates are normally cross-resistant to all members of the azole family.

Antihormonal activity

As an antiandrogen, ketoconazole operates through at least two mechanisms of action. First, and most notably, high oral doses of ketoconazole (e.g. 40 mg three times per day) block both testicular and adrenal androgen biosynthesis, leading to a reduction in circulating testosterone levels. It produces this effect through inhibition of 17α-hydroxylase and 17,20-lyase, which are involved in the synthesis and degradation of steroids, including the precursors of testosterone. Due to its efficacy at reducing systemic androgen levels, ketoconazole has been used with some success as a treatment for androgen-dependent prostate cancer. Second, ketoconazole is an androgen receptor antagonist