Itraconazole: Use, Mechanism of Action, and Antifungal Dosing
The itraconazole is a pharmacological agent belonging to the triazole class, primarily used in the treatment of various Unlike other fungal infections.
Therapeutic Applications of Itraconazole
The spectrum of action of itraconazole covers a wide range of fungal pathogens. It is effective against:
- Dermatophytes (causing ringworm infections).
- Yeasts, including those responsible for Candida and Malassezia infections. Candida y Malassezia.
- Severe systemic fungal systemic infections such as histoplasmosis, aspergillosis, coccidioidomycosis, and chromoblastomycosis.
Additionally, itraconazole is occasionally used off-label, as recent studies have indicated that it may inhibit the growth of basal cell carcinoma carcinoma of squamous cell. It is also used in the management of certain inflammatory skin diseases, such as atopic eczema, seborrheic dermatitis, or psoriasis, if fungal or yeast colonization is suspected as a contributing factor to the pathology.[1,2] inflammatory, such as eczema atopic, , dermatitis Fulminant rosacea. or psoriasis, if fungal or yeast colonization is suspected as a contributing factor to the pathology.[1,2]
Mechanism of Action of Itraconazole
The functioning of itraconazole is based on its ability to bind to the fungal muscle enzymes p450 enzymes. This interaction interrupts the synthesis of ergosterol, the essential component that forms the structure of the microorganism's cell wall.
Administration and Pharmacokinetics of Itraconazole
In New Zealand, itraconazole is prescribed by medical prescription in the form of 100 mg capsules, and is also available as a liquid preparation (10 mg/ml). A generic version, called Itrazol, may be funded under certain conditions. Sporanox™, developed by Janssen-Cilag, is the registered trademark that markets itraconazole preparations. The Sporanox oral solution is subsidized through the Special Authority for the treatment of children with immunodeficiencies and related fungal infections.
To optimize oral absorption, it is recommended to take the medication concurrently with a high-fat meal or an acidic beverage, such as orange juice. The active ingredient binds strongly to plasmaproteins**proteins** such as albumin and tends to accumulate in adipose tissue, as well as in the skin and and nail. nails. The elimination half-life in the bloodstream is one to three days. The remainder of the drug is subsequently excreted through feces and urine, after being metabolized by the liver into inactive compounds.
It is important to note that itraconazole concentrations in skin tissue can be three to ten times higher than those found in the blood. This characteristic allows the therapeutic effect to persist persist in the skin for up to four weeks after discontinuing treatment, and in the nails, it can remain detectable for almost a year.
Common Dosing Regimens for Itraconazole
Various dosing protocols have proven effective for the use of itraconazole. Below are the typical guidelines, which may be repeated or extended for several months depending on clinical need:
- Tinea corporis, tinea cruris: 200 mg daily for one week, or 100 mg daily for two weeks.
- Tinea pedis, tinea manuum: 200 mg twice daily for one week, or 100 mg daily for 2 to 4 weeks.
- Acute atrophic vulvovaginal: 200 mg twice daily for one day, or 200 mg daily for three days.
- Oral candidiasis: 100 mg daily for two weeks.
- Tinea unguium: 200 mg/day for 6-8 weeks (fingernails) or 3-4 months (toenails); alternatively, 200 mg twice daily for 7 days, repeated monthly for 2 months (hands) or 3-4 months (feet).
- Pityriasis Pityriasis versicolor: 200 mg/day for...
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- 10 days, with a prophylactic dose of 200 mg once a month for 6 months.
Itraconazole dosing in the pediatric population is generally established at 5 mg per kilogram of body weight daily, with a maximum limit of 200 mg per day. However, its use in children is strictly reserved for exceptional therapeutic situations.
Common and Rare Side Effects of Itraconazole
Itraconazole is perceived as a pharmacologically safe antifungal agent. Adverse effects, which tend to be mild, are more frequent when administered in long-term treatments.
- Gastrointestinal discomfort: Nausea and vomiting are reported in approximately 5% of patients.
- Constipation.
- Headache.
- Feeling of dizziness or vertigo.
- Alterations in liver function tests (detected in up to 5% in prolonged therapies, and 2% in pulse therapies). It is essential to note that the development of severe liver disease is a rare event.
- Allergic skin reactions, including rash and hives.
- Endocrine effects that may manifest as gynecomastia (enlargement of the breasts in men) and suppression of adrenal function.
- Paresthesia (tingling in upper and lower extremities), a very infrequent side effect.
- Congestive heart failure: Extreme caution is required when prescribing itraconazole to patients with a history of pre-existing cardiac conditions.
Generally, the use of itraconazole during pregnancy is advised against. Although the drug is excreted in minimal amounts in breast milk, its administration to nursing mothers should only be considered if the therapeutic benefit justifies the potential risk.
Critical Drug Interactions with Itraconazole
Itraconazole has a significant profile of interactions with other medications, which requires careful management of polypharmacy.
Because optimal absorption of itraconazole depends on the acidic stomach environment, it is crucial to space out intake. This means that antacids, H2 receptor antagonists (such as cimetidine, famotidine, ranitidine), and proton pump inhibitors (such as omeprazole) should not be administered until two hours after taking itraconazole.
Furthermore, itraconazole acts as a P-glycoprotein inhibitor, resulting in an increase in the plasma concentration of certain concomitant drugs.
Patients undergoing treatment with itraconazole must categorically discontinue the use of the following medications:
- HMG-CoA reductase inhibitors (statins): Includes atorvastatin, lovastatin, and simvastatin. Safe alternatives are fluvastatin, rosuvastatin, and pravastatin. The combination can induce serious toxicity, manifested by severe myalgia and muscle weakness.
- Cisapride.
- Short-acting benzodiazepines: Specifically midazolam and triazolam.
- Sedating antihistamines: Such as astemizole (Hismanal®) and terfenadine (Teldane®); the latter are no longer available in the New Zealand market.
Itraconazole potentiates the anticoagulant effect of drugs such as warfarin or dabigatran, increasing the risk of bleeding.
In the following cases, a dosage adjustment is essential, typically involving a reduction in the dose of the associated medication:
- Warfarin.
- Digoxin.
- Methylprednisolone.
- Cyclosporine.
- Tacrolimus.
- Vinca alkaloids.
It may be necessary to decrease the dose of the following drugs if side effects related to drug concentration are observed:
- Quinidine.
- Calcium channel blockers.
- Antidiabetic medications of the sulfonylurea class (including tolbutamide, glibenclamide, gliclazide, glipizide).
The following therapeutic agents decrease serum levels of itraconazole, which could compromise its antifungal efficacy:
- Rifampicin.
- Isoniazid.
- Phenytoin.
- Carbamazepine.
It is important to note that itraconazole is not considered to have clinically relevant interactions with the oral contraceptive pill.
