Itraconazole

Introduction Overview

Generic Name

Itraconazole

Brand Name

Sporanox, Tolsura, Onmel, Sporanox PulsePak

Dosage Form

Oral capsule (100 mg; 65 mg), Oral solution (10 mg/mL)

Drug Class

Azole antifungals

Pharmacokinetics

Absorption:
Itraconazole exhibits variable oral absorption influenced by the formulation and gastric conditions. The oral capsule formulation is best absorbed when taken with food, as it requires an acidic gastric environment to improve bioavailability. In contrast, the oral solution should be taken on an empty stomach to optimize absorption, as food and elevated stomach pH reduce its effective bioavailability. Gastric pH modifying agents such as proton pump inhibitors and H2 antagonists can significantly decrease itraconazole absorption, affecting plasma drug levels and therapeutic efficacy. For optimal absorption, patients are often advised to take capsules with an acidic beverage if concomitant use of acid-reducing agents is unavoidable. After oral administration, peak plasma concentrations are typically reached within 3 to 5 hours, but this can vary depending on the preparation.

Distribution:
Itraconazole is highly lipophilic, leading to extensive tissue distribution with a large volume of distribution (approximately 700 L). It accumulates in keratin-containing tissues such as skin, nails, and hair, which supports its effectiveness in treating dermatophytic and onychomycosis infections. Plasma protein binding of itraconazole is high, exceeding 99%, primarily to albumin, which limits free drug levels but maintains sustained systemic concentrations. The drug concentrates in fatty tissues and the lungs, explaining its utility in treating pulmonary fungal infections. Penetration into the cerebrospinal fluid is poor. The drug’s extensive tissue affinity and accumulation contribute to its prolonged half-life and therapeutic effect despite relatively low plasma concentrations.

Metabolism:
Itraconazole is extensively metabolized by the hepatic cytochrome P450 enzyme system, particularly CYP3A4, into multiple metabolites. The major metabolite, hydroxy-itraconazole, retains antifungal activity and contributes substantially to the overall pharmacological effect. The metabolism is subject to significant interindividual variability due to genetic factors, concomitant medications affecting CYP3A4 activity, and hepatic function status. These factors can influence plasma concentrations, risk of toxicity, and therapeutic outcomes. Due to its metabolism via CYP3A4, itraconazole has a high potential for drug-drug interactions. Metabolic clearance and transformation are saturable processes that can be influenced by disease states and patient-specific characteristics.

Elimination:
The elimination half-life of itraconazole varies widely, usually between 17 and 42 hours, but effective plasma levels can be sustained longer due to tissue reservoir release. Elimination occurs primarily via biliary excretion into feces, with less than 1% excreted unchanged in the urine. Enterohepatic recirculation contributes to prolonged drug presence in systemic circulation. Renal clearance is minimal, which is clinically relevant in patients with renal impairment as dose adjustments are usually not necessary. Hepatic impairment, however, can markedly reduce clearance, increasing systemic exposure and risk of toxicity. The prolonged elimination phase supports the once or twice daily dosing regimen and necessitates careful monitoring during long-term therapy.

Dosage Forms

Available Dosage Forms:
Itraconazole is commercially available mainly as oral capsules and oral solution. The capsule formulations come in 65 mg and 100 mg strengths. The oral solution is available at a concentration of 10 mg/mL. Additionally, the Sporanox PulsePak utilizes a special dosing regimen but contains oral capsules. These different dosage forms support varying clinical needs, absorption profiles, and patient tolerability.

Dosages for Adults and Adolescents:
For systemic fungal infections, the usual adult dosage of itraconazole capsules ranges from 100 mg to 200 mg once or twice daily depending on the severity and type of infection. The oral solution may be dosed similarly but is preferred in certain infections for improved absorption. For onychomycosis, the typical course involves 200 mg once daily for 12 weeks. The Sporanox PulsePak employs intermittent dosing schedules for toenail infections to reduce adverse effects and improve compliance. Dosage adjustments may be necessary based on infection site, organism susceptibility, and patient response.

Specific Patient Populations:
In patients with hepatic impairment, itraconazole clearance is reduced, increasing systemic exposure; thus, careful dose monitoring and perhaps dose reduction are recommended. In renal impairment, no dosage adjustment is typically necessary due to minimal renal excretion. In pediatric populations, itraconazole dosing must be carefully considered with limited data extrapolated mainly from adult studies. The oral solution may be preferred for children due to difficulty swallowing capsules. Because of a potential risk of cardiotoxicity including congestive heart failure, itraconazole is contraindicated in patients with a history of heart failure. Pregnant women should avoid itraconazole due to fetal toxicity risks. Drug exposure and efficacy can also be impacted by co-administration with acid-suppressing medications, necessitating individualized regimen planning.

Mechanism Of Action

Itraconazole exerts its antifungal effects primarily by inhibiting the cytochrome P450-dependent enzyme 14-alpha-demethylase, a key enzyme in the biosynthesis of ergosterol, an essential sterol component of fungal cell membranes. By blocking ergosterol synthesis, itraconazole disrupts the integrity and function of the fungal cell membrane, leading to increased membrane permeability, impaired membrane-bound enzyme functions, and ultimately fungal cell death or growth inhibition.

At the molecular level, itraconazole binds to the heme iron of the 14-alpha-demethylase enzyme, preventing the demethylation of lanosterol to ergosterol. This blockage causes accumulation of toxic methylated sterol precursors that disrupt membrane structure. The specificity of itraconazole for fungal cytochrome P450 enzymes over mammalian isoenzymes underpins its antifungal selectivity, though some inhibition of human CYP450 enzymes contributes to drug interactions and potential toxicity.

Cellularly, the depletion of ergosterol results in compromised fungal cell walls and interruption of cell division and replication processes. This effect is more pronounced in fungi with high ergosterol content, such as Candida spp., Aspergillus spp., and dermatophytes. Itraconazole also demonstrates fungistatic to fungicidal properties depending on the concentration and organism susceptibility. Research indicates that itraconazole can modulate fungal biofilm growth, enhancing treatment efficacy in persistent infections.

Clinically, the mechanism supports the use of itraconazole in a broad spectrum of fungal infections including candidiasis, aspergillosis, blastomycosis, and histoplasmosis. Compared with other azole antifungals like fluconazole and voriconazole, itraconazole features a broader spectrum that includes certain molds and dermatophytes. Studies have demonstrated itraconazole’s enhanced tissue penetration and keratin affinity aiding nail and skin infections therapy, an advantage over other azoles. Ongoing research also explores its role in combination therapies and potential immunomodulatory properties.

Pharmacological Actions

Inhibits fungal cytochrome P450 14-alpha-demethylase enzyme, disrupting ergosterol synthesis.
Compromises fungal cell membrane integrity leading to increased permeability and cell death or growth inhibition.
Exhibits fungistatic to fungicidal effects depending on fungal species and drug concentration.
Demonstrates broad-spectrum antifungal activity against yeasts, molds, dermatophytes, and dimorphic fungi.
Displays keratinophilic properties enabling treatment of nail and skin fungal infections.
Produces active hydroxy-itraconazole metabolite contributing to overall antifungal activity.
Interferes with fungal biofilm formation, enhancing efficacy against persistent fungal infections.
Induces inhibition of human CYP450 enzymes potentially affecting metabolism of other drugs.
Exhibits moderate anti-inflammatory effects secondary to fungal clearance.
Inhibits fungal cell replication and division by disrupting membrane-associated processes.

Therapeutic Or Clinical Uses

Treatment of systemic and mucocutaneous candidiasis, including oropharyngeal and esophageal infections.
Management of aspergillosis and other invasive mold infections.
Treatment of dermatophytic infections such as tinea corporis, tinea cruris, and onychomycosis (toenail and fingernail fungus).
Therapy for endemic mycoses, including blastomycosis, histoplasmosis, and paracoccidioidomycosis.
Prophylaxis against fungal infections in immunocompromised patients, such as those post-transplant or undergoing chemotherapy.
Treatment of fungal infections resistant or intolerant to other antifungals.
Adjunct therapy in disseminated fungal infections to reduce fungal burden.
Treatment of fungal infections of the lungs and respiratory tract.
Management of fungal urinary tract infections caused by susceptible Candida species.
Utilized in cutaneous or subcutaneous fungal infections refractory to topical treatment.

Side Or Adverse Effects

Headache, dizziness, drowsiness, and general fatigue reported commonly.
Gastrointestinal disturbances including nausea, vomiting, diarrhea, constipation, and stomach pain.
Hepatotoxicity indicated by abnormal liver function tests and possible liver enzyme elevation.
Rash, itching, and other hypersensitivity skin reactions.
Peripheral edema and fluid retention potentially linked to congestive heart failure risk.
Cardiac adverse effects such as congestive heart failure, tachycardia, and palpitations.
Hypokalemia manifesting as leg cramps, constipation, irregular heartbeats, and muscle weakness.
Pancreatitis presenting as severe upper abdominal pain radiating to the back, nausea, and vomiting.
Neurologic symptoms including blurred or double vision, tinnitus, and numbness or tingling sensations.
Taste disturbances including unusual or unpleasant taste sensations.
Hair loss (alopecia) reported in some patients during prolonged therapy.
Sexual dysfunction such as impotence or erectile difficulties.
Menstrual irregularities or changes in menstrual periods.
Allergic reactions including severe skin rash, hives, and angioedema.
Potential for liver failure in rare but serious cases necessitating monitoring.

Precautions

Avoid use in patients with history of congestive heart failure due to risk of worsening cardiac status.
Use caution in patients with liver impairment; monitor hepatic function tests regularly.
Avoid concomitant use with strong CYP3A4 inhibitors or inducers to prevent adverse drug interactions.
Do not combine with certain medications including cisapride, simvastatin, and other drugs metabolized by CYP3A4 without medical supervision.
Pregnant women should avoid itraconazole due to teratogenicity and fetal risk.
Use effective contraception during treatment and for at least two months after discontinuation.
Avoid use in patients allergic to itraconazole or other azole antifungals such as fluconazole or ketoconazole.
Monitor for signs of hepatotoxicity, neurotoxicity, and electrolyte imbalance during prolonged therapy.
Assess renal function prior to and during treatment in patients with preexisting renal disorders.
Avoid antacids or acid-reducing agents close to itraconazole dosing times unless taken with acidic beverage.
Cautiously administer in patients with cystic fibrosis or other chronic pulmonary illnesses.
Avoid abrupt discontinuation to prevent fungal resistance or recurrence of infection.
Use with caution in immunocompromised patients; monitor closely for secondary infections.
Educate patients not to share medications and to adhere strictly to prescribed dosage and duration.
Advise to report symptoms indicative of congestive heart failure or severe allergic reactions promptly.

Warnings

Contraindicated in patients with congestive heart failure or history of heart problems.
Potential for life-threatening drug interactions when taken with CYP3A4-metabolized medications such as cisapride, simvastatin, and others.
Hepatotoxicity can be severe; discontinue therapy if significant liver dysfunction or jaundice develops.
May cause fetal harm; pregnancy must be avoided during therapy and for at least two months following treatment.
Risk of congestive heart failure symptoms including cough with mucus, shortness of breath, and swelling; immediate medical evaluation required.
Concomitant use with certain heart rhythm, cholesterol-lowering, and psychotropic medications may cause serious cardiac events.
Monitor potassium levels due to risk of hypokalemia which may precipitate arrhythmias.
Caution advised in patients with renal or hepatic impairment because of altered pharmacokinetics and increased toxicity risk.
Avoid use in patients receiving oral midazolam or triazolam as concomitant use may cause excessive sedation or respiratory depression.
Use caution in elderly due to increased susceptibility to adverse cardiac and hepatic effects.
Potential for drug-induced pancreatitis; observe for upper abdominal pain and vomiting.
Avoid use with drugs such as lomitapide or lovastatin that could compound muscle toxicity risk.
Close monitoring required when used with antiarrhythmics or antihypertensives due to potential pharmacodynamic interactions.
Risk of severe hypersensitivity reactions including Stevens-Johnson Syndrome with itraconazole use, though rare.
Patients must be monitored for unusual bruising or bleeding as azoles may influence coagulation parameters.

Contraindication

Known hypersensitivity or allergy to itraconazole or other azole antifungal agents such as fluconazole and ketoconazole.
History or presence of congestive heart failure or ventricular dysfunction.
Concurrent use with drugs highly dependent on CYP3A4 metabolism that may cause life-threatening interactions (e.g., cisapride, pimozide, quinidine).
Patients with severe liver impairment or hepatic failure due to high risk of toxicity.
Use during pregnancy due to teratogenic potential and risk of fetal harm.
Severe hypersensitivity reactions to itraconazole formulations.
Concurrent use with oral midazolam or triazolam due to risk of excessive sedation and respiratory depression.
Patients receiving ergot alkaloids such as ergotamine or dihydroergotamine due to risk of ergot toxicity.
Concomitant administration with certain cholesterol-lowering agents like simvastatin or lovastatin at high doses.
Use with drugs that prolong QT interval unless monitored closely due to risk of cardiac arrhythmia.
Patients with caution if receiving drugs like disopyramide, dofetilide, dronedarone, or ranolazine due to possible additive cardiac toxicity.
Patients with known QT prolongation or history of torsades de pointes.
Use contraindicated with certain psychotropic medications (lurasidone, pimozide).
Patients with hypersensitivity to excipients of the itraconazole formulation.

Drug Interactions

Potent CYP3A4 inhibitor leading to increased plasma levels of concomitant drugs metabolized by CYP3A4 (e.g., simvastatin, lovastatin) increasing risk of toxicity.
Contraindicated with cisapride, pimozide, quinidine, disopyramide due to risk of QT prolongation and serious cardiac arrhythmias.
Increased plasma concentrations of calcium channel blockers such as felodipine, nisoldipine, and eplerenone.
Elevated levels of benzodiazepines (oral midazolam, triazolam) causing prolonged sedation and respiratory depression.
Interaction with methadone may alter plasma levels affecting efficacy and safety.
Concomitant use with certain antipsychotics like lurasidone increases risk of adverse neurological and cardiac events.
Increased levels and toxicity risk of cholesterol-lowering agents (lovastatin, simvastatin, lomitapide).
Potentially increased concentration of antiarrhythmic agents (dronedarone, dofetilide) increasing risk for arrhythmias.
Interaction with ergot alkaloids (ergotamine, dihydroergotamine, methylergonovine) may cause ergot toxicity.
Reduced clearance of colchicine in patients with liver or kidney disease increasing risk of toxicity.
Decreased absorption with antacids and acid-reducing agents; use with acidic beverages to mitigate this effect.
Potentially altered levels of oral contraceptives requiring additional contraceptive measures.
Interactions with immunosuppressants such as cyclosporine leading to increased drug levels.
Effects on P-glycoprotein substrates modifying their absorption and clearance.
Cautious use with drugs like irinotecan and ranolazine which have narrow therapeutic windows.

Preparations Of The Drug

Oral capsules containing 65 mg and 100 mg itraconazole for systemic fungal infections.
Oral solution formulation at 10 mg/mL concentration for enhanced bioavailability and use in patients unable to swallow capsules.
Sporanox PulsePak featuring a special capsule dosing schedule for onychomycosis treatment.
Various generic formulations for both capsules and oral solution available in the market.
Commercially branded preparations include Sporanox, Tolsura, and Onmel with distinct pharmacokinetic profiles.
Capsules are indicated to be taken with food for optimal absorption, whereas oral solution is taken on empty stomach.
Stable at room temperature away from moisture, heat, and light to maintain potency.
Accompanying dosing syringes provided with the oral solution for precise measurement.
Pharmaceutical forms not intended to be interchanged without physician approval due to differences in absorption.
No intravenous formulation widely available; oral forms predominate clinical use.
Packaging with detailed instructions to avoid medication errors between brands and dosage forms.
Formulations designed to improve patient compliance through convenient dosing schedules.
Liquid form beneficial for pediatric and elderly patients or those with swallowing difficulties.
Capsule fills and excipients formulated to minimize gastrointestinal irritation.
Each preparation undergoes rigorous quality control to ensure consistent potency and safety.