About This Calculator

The Voriconazole Dose Calculator provides dosing recommendations for both pediatric and adult patients based on standard clinical guidelines. It determines appropriate loading and maintenance doses for intravenous (IV) and oral (PO) administration, taking into account patient weight, age, and hepatic function.

This tool is designed for healthcare professionals as a decision support aid and is not a substitute for clinical judgment. All calculated doses should be verified against primary literature and institutional protocols.

Understanding the Outputs

The calculator provides the following key outputs based on the information entered:

• Loading Dose: The initial higher dose given to rapidly achieve therapeutic drug concentrations. This is calculated for both IV and PO routes in adults, but typically only for the IV route in children.
• Maintenance Dose: The regular dose required to maintain therapeutic concentrations after the loading dose. The calculation includes adjustments for mild-to-moderate hepatic impairment (Child-Pugh Class A/B).
• Weight-Based Dosing: For relevant regimens (e.g., IV administration), the output displays both the total calculated dose (in mg) and the corresponding mg/kg basis.
• Therapeutic Drug Monitoring (TDM) Guidance: If a trough level is provided, the tool offers an interpretation (subtherapeutic, therapeutic, or supratherapeutic) and a general recommendation for dose adjustment.
• Clinical Alerts: Important warnings, such as the risk of vehicle accumulation with IV administration in patients with a CrCl <50 mL/min, are highlighted.

How to Use the Tool

To calculate a dose, follow these steps:

1. Select Patient Population: Choose between "Adult (≥ 15 years)" and "Pediatric (2 to <15 years)".
2. Enter Patient Weight: Input the patient's weight and select the correct unit (kg or lbs). The calculation uses actual body weight.
3. Enter Patient Age: Provide the patient's age in years.
4. Select Route of Administration: Choose "Intravenous (IV)" or "Oral (PO)".
5. Specify Hepatic Function: Select "Normal," "Mild-to-Moderate (Child-Pugh A/B)," or "Severe (Child-Pugh C)." Dosing is not recommended for severe impairment.
6. Enter Creatinine Clearance (if applicable): If the IV route is selected, you must enter the CrCl (in mL/min) to assess for potential accumulation of the IV vehicle.
7. Calculate: Click "Calculate Dose" to see the results. For TDM guidance, check the optional box and enter a measured trough level.

Voriconazole Dosing Overview

Adult Dosing (≥15 years)

• Intravenous (IV): Loading dose of 6 mg/kg every 12 hours for 2 doses, followed by a maintenance dose of 4 mg/kg every 12 hours.
• Oral (PO): For patients ≥40 kg, a loading dose of 400 mg every 12 hours for 2 doses, followed by a maintenance dose of 200 mg every 12 hours. For patients <40 kg, these doses are halved (200 mg loading, 100 mg maintenance).

Pediatric Dosing (2 to <15 years)

• Intravenous (IV): Loading dose of 9 mg/kg every 12 hours for 2 doses, followed by a maintenance dose of 8 mg/kg every 12 hours.
• Oral (PO): A maintenance dose of 9 mg/kg (up to a maximum of 350 mg) every 12 hours. An oral loading dose is not typically recommended in this population.

Dose Adjustments

• Hepatic Impairment (Child-Pugh A/B): The loading dose remains the same, but the maintenance dose should be reduced by 50%.
• Renal Impairment (CrCl <50 mL/min): While voriconazole itself is cleared hepatically, the intravenous vehicle (SBECD) is cleared renally and can accumulate. The use of IV voriconazole should be avoided in these patients unless the benefit outweighs the risk. Oral administration is preferred.

Switching Between IV and Oral

Patients who are clinically stable may be switched from intravenous to oral administration. A loading dose is not required when switching from IV to oral therapy. The standard oral maintenance dose can typically be initiated 12 hours after the last intravenous dose.

Missed Dose Guidance

If a patient misses a dose, they should take it as soon as they remember. However, if it is nearly time for the next scheduled dose, they should skip the missed dose and resume their regular dosing schedule. Patients should not take a double dose to make up for a missed one.

Safety Alerts

Frequently Asked Questions

Why is Creatinine Clearance (CrCl) required for IV but not oral administration?

The intravenous formulation of voriconazole contains a solubilizing agent, sulfobutylether-beta-cyclodextrin (SBECD), which is eliminated by the kidneys. In patients with a CrCl below 50 mL/min, SBECD can accumulate, and its effects are not well-defined. Therefore, oral therapy is preferred in these patients.

What is the target trough level for voriconazole?

The generally accepted therapeutic trough concentration for voriconazole is between 1.0 and 5.5 mcg/mL. Levels below 1.0 mcg/mL may be associated with treatment failure, while levels above 5.5 mcg/mL are associated with an increased risk of toxicity.

Why isn't a loading dose recommended for children on the oral formulation?

Clinical studies and guidelines for pediatric patients have established the efficacy of a maintenance-only oral dosing strategy. The higher weight-based maintenance dose (9 mg/kg) helps achieve therapeutic concentrations without a preceding loading dose.

What should I do for a patient with severe liver disease (Child-Pugh Class C)?

Voriconazole is not recommended for patients with severe hepatic impairment (Child-Pugh C) unless a careful benefit-risk assessment justifies its use. If used, dosing information is limited, and intensive monitoring for toxicity is required.

How does the calculator define a "pediatric" patient?

The calculator uses the pediatric dosing regimen for patients aged 2 to less than 15 years, consistent with prescribing information. Older adolescents (15+ years) are typically dosed according to adult guidelines.

Does this calculator use actual, ideal, or adjusted body weight?

The calculations are based on the patient's actual body weight, as entered into the tool. This is the standard practice for voriconazole dosing, including in obese patients.

Does the calculator account for drug-drug interactions?

No. Voriconazole is a substrate and inhibitor of several cytochrome P450 enzymes (CYP2C19, CYP2C9, and CYP3A4). It has numerous significant drug-drug interactions that can alter its concentration or the concentration of other drugs. Always perform a comprehensive medication review.

When should a trough level be drawn for TDM?

Trough levels should be drawn just before the next scheduled dose (within 30 minutes) after the patient has reached steady-state, which is typically after 5 to 7 days of consistent maintenance dosing.

References

1. VFEND® (voriconazole) tablets, for oral use; for oral suspension; for injection, for intravenous use. U.S. Prescribing Information. Pfizer Inc. Revised: June 2023. FDA.gov.
2. Patterson TF, Thompson GR 3rd, Denning DW, et al. Practice Guidelines for the Diagnosis and Management of Aspergillosis: 2016 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2016;63(4):e1-e60. doi:10.1093/cid/ciw326.
3. Vfend (voriconazole) Summary of Product Characteristics (SmPC). European Medicines Agency. EMA.europa.eu.
4. Ashbee HR, Barnes RA, Johnson EM, et al. Therapeutic drug monitoring (TDM) of antifungal agents: guidelines from the British Society for Medical Mycology. J Antimicrob Chemother. 2014;69(5):1162-1176. doi:10.1093/jac/dkt508.