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Voriconazole

Voriconazole: Generic Medication Overview

Voriconazole is an antifungal medication belonging to the triazole class. It is available in a 200 mg oral pill form and is prescribed by healthcare providers in Hong Kong for the treatment of serious fungal infections. Voriconazole is a prescription-only (Rx) drug regulated by the Hong Kong Department of Health.

How Voriconazole Works in the Body

Voriconazole inhibits the fungal enzyme lanosterol 14α-demethylase, a key step in the synthesis of ergosterol, which is essential for fungal cell membrane integrity. By blocking this pathway, the drug disrupts membrane formation, leading to fungal cell death. The medication is absorbed well after oral administration, reaching peak plasma concentrations within 2 hours. It is metabolized primarily by the liver enzymes CYP2C19, CYP2C9 and CYP3A4, and has a half-life of about 6 hours in healthy adults.

Conditions Treated by Voriconazole

Voriconazole is approved by the Hong Kong regulatory authorities for the following indications:

• Invasive aspergillosis in immunocompromised patients
• Serious infections caused by Candida species, including candidemia when other agents are unsuitable
• Infections caused by Scedosporium and Fusarium species when alternative therapies are ineffective

These uses are based on clinical trial data demonstrating superior efficacy compared with older azoles for invasive aspergillosis.

Off-Label and Investigational Applications

• Empirical therapy for febrile neutropenia where fungal infection is suspected but not yet identified.
• Treatment of rare mold infections such as Zygomycetes (off-label; limited evidence).

Off-label use requires medical supervision and individualized risk assessment.

Who Should Not Use Voriconazole?

Absolute Contraindications

• Known hypersensitivity to voriconazole or any triazole antifungal
• Concurrent use of drugs that cause serious QT-interval prolongation (e.g., certain antiarrhythmics)

Relative Contraindications

• Severe hepatic impairment (Child-Pugh class C) - dose adjustment needed
• Pregnancy (Category D): potential risk to the fetus; use only if the benefit outweighs the risk
• Co-administration with strong CYP3A4 inducers (e.g., rifampin) - may reduce voriconazole efficacy

Special Populations

• Renal impairment: no dose change required unless receiving the intravenous formulation, which contains cyclodextrin that can accumulate.
• Elderly: monitor liver function closely; dose adjustments may be necessary based on tolerability.

Safety Profile: Side Effects and Interactions

Common Side Effects

• Visual disturbances (e.g., blurred vision, altered color perception) - usually transient
• Elevated liver enzymes (ALT, AST) - monitor liver function tests regularly
• Skin rash or mild itching

Serious Adverse Events

• Hepatotoxicity leading to jaundice or liver failure - seek immediate medical attention if symptoms develop
• Severe photosensitivity and risk of skin cancer with long-term use
• QT-interval prolongation that can precipitate arrhythmias

Drug Interactions

• Major: Co-administration with rifampin, carbamazepine, phenytoin, or phenobarbital can drastically lower voriconazole levels.
• Moderate: Use with warfarin, tacrolimus, sirolimus, or cyclosporine may require dose adjustments and therapeutic drug monitoring.
• Interactions are primarily mediated through CYP2C19, CYP2C9 and CYP3A4 pathways.

Food and Lifestyle Interactions

• Avoid excessive grapefruit juice, which can increase voriconazole concentrations.
• Alcohol consumption should be limited, as both alcohol and voriconazole are metabolized by the liver.
• No specific driving restrictions, but visual disturbances may temporarily impair vision; caution is advised.

How to Take Voriconazole

• Standard oral dosing: 200 mg pill taken every 12 hours.
• Loading dose: In some severe infections, clinicians may start with a higher initial dose (e.g., 6 mg/kg) for the first 24 hours, followed by the standard regimen; this decision is made by the prescribing physician.
• Administration: Swallow the tablet whole with a glass of water. Food does not significantly affect absorption, but taking the medication with food may reduce gastrointestinal upset.
• Missed dose: Take the missed dose as soon as remembered if the next scheduled dose is ≥ 6 hours away; otherwise, skip the missed dose and resume the regular schedule. Do not double the dose.
• Overdose: Symptoms may include severe nausea, vomiting, visual changes, and liver dysfunction. Seek emergency medical care; supportive measures are the primary treatment.
• Discontinuation: Tapering is not routinely required, but abrupt cessation may lead to recurrence of infection. Follow the prescriber’s instructions for stopping therapy.

Monitoring and Follow-Up

• Liver function tests (ALT, AST, bilirubin) at baseline and at least weekly during the first month, then periodically thereafter.
• Renal function monitoring when the intravenous formulation is used.
• Electrolytes and ECG if the patient has cardiac risk factors or is on other QT-prolonging agents.
• Therapeutic drug monitoring (trough levels) may be performed for dose optimization, especially in patients with liver disease or those taking interacting medications.

Storage and Handling

• Store the tablets at room temperature (15 °C-30 °C) in a dry place, away from direct sunlight and moisture.
• Keep the medication out of reach of children.
• Do not use tablets that are discolored, cracked, or past the expiration date printed on the packaging.

Medication-Specific Glossary

CYP450 Enzymes

A group of liver enzymes (including CYP2C19, CYP2C9, CYP3A4) that metabolize many drugs; voriconazole is both a substrate and inhibitor of these enzymes.

QT Prolongation

An elongation of the heart’s electrical repolarization phase, measurable on an ECG; can increase the risk of irregular heart rhythms.

Therapeutic Drug Monitoring (TDM)

Measuring drug concentrations in the blood to ensure efficacy while minimizing toxicity; commonly used for voriconazole due to variable metabolism.

Medical Disclaimer

This article provides educational information about voriconazole and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.