Voriconazole Dosing
For adults, initiate voriconazole with a loading dose of 6 mg/kg IV every 12 hours for two doses (or 400 mg PO every 12 hours for two doses), followed by a maintenance dose of 4 mg/kg IV every 12 hours (or 200-300 mg PO every 12 hours); in patients with mild to moderate hepatic impairment (Child-Pugh Class A or B), reduce the maintenance dose by 50% while keeping the loading dose unchanged. 1
Adult Dosing Regimen
Standard Dosing
The FDA-approved regimen for invasive fungal infections follows a two-phase approach 1:
Loading Phase (Day 1):
- IV: 6 mg/kg every 12 hours for 2 doses
- PO: 400 mg every 12 hours for 2 doses (6 mg/kg for patients <40 kg)
Maintenance Phase:
- IV: 3-4 mg/kg every 12 hours
- PO: 200-300 mg every 12 hours (100-150 mg for patients <40 kg)
The oral bioavailability of voriconazole is excellent (>90%), and switching from IV to oral is appropriate once clinical improvement occurs 2. Administer oral voriconazole at least one hour before or after meals, as food decreases absorption 1.
Indication-Specific Considerations
For candidemia and invasive candidiasis, the 2016 IDSA guidelines recommend voriconazole primarily as step-down oral therapy for infections due to C. krusei or voriconazole-susceptible C. glabrata 2. The maintenance dose is typically 3-4 mg/kg IV or 200 mg PO every 12 hours 2.
For invasive aspergillosis, use the 4 mg/kg IV or 200 mg PO maintenance dose 2. The median duration of IV therapy in clinical trials was 10 days, with oral therapy continuing for a median of 76 days 1.
Pediatric Dosing
For adolescents 12-14 years weighing ≥50 kg and those ≥15 years regardless of weight, use the adult dosing regimen 1.
For younger children (2-14 years), higher weight-based doses are required due to different pharmacokinetics 3:
- Loading: 9 mg/kg IV every 12 hours for 2 doses
- Maintenance: 8 mg/kg IV every 12 hours (or 9 mg/kg PO every 12 hours, maximum 350 mg per dose)
Children exhibit linear pharmacokinetics unlike adults who show nonlinear metabolism, necessitating these higher doses to achieve comparable drug exposure 4, 5.
Hepatic Impairment Adjustments
This is the only triazole requiring dose reduction in hepatic dysfunction 2.
Mild to Moderate Hepatic Impairment (Child-Pugh Class A or B):
- Use standard loading doses (6 mg/kg IV or 400 mg PO every 12 hours for 2 doses)
- Reduce maintenance dose by 50%: 2 mg/kg IV or 100 mg PO every 12 hours 1
Severe Hepatic Impairment (Child-Pugh Class C):
- No established dosing recommendations exist 1
- Use only if benefits outweigh risks, with close monitoring for toxicity 1
- Recent evidence suggests doses <2 mg/kg/dose may be appropriate in advanced cirrhosis to prevent drug accumulation 6
Monitor liver function tests closely, as voriconazole can cause hepatotoxicity including elevated transaminases and jaundice 2. Patients with baseline ALT/AST up to 5× ULN were included in clinical trials without requiring dose adjustment, but continued monitoring is essential 1.
Renal Impairment Considerations
Oral voriconazole requires no dose adjustment in renal impairment 1.
IV voriconazole is not recommended when creatinine clearance <50 mL/min due to accumulation of the cyclodextrin vehicle (SBECD), which may cause nephrotoxicity 2, 1. However, retrospective data suggest this concern may be overstated 2. Switch to oral formulation in patients with moderate to severe renal dysfunction 1.
Dose Adjustments for Inadequate Response or Intolerance
If therapeutic response is inadequate:
- Increase oral dose from 200 mg to 300 mg every 12 hours (or 100 mg to 150 mg for patients <40 kg)
- Increase IV dose from 3 mg/kg to 4 mg/kg every 12 hours 1
If patient cannot tolerate higher doses:
- Reduce oral dose in 50 mg decrements to minimum of 200 mg every 12 hours
- Reduce IV dose from 4 mg/kg to 3 mg/kg every 12 hours 1
Critical Monitoring and Safety Considerations
Therapeutic Drug Monitoring (TDM)
TDM is strongly recommended due to significant pharmacokinetic variability 2, 4. Target trough concentrations:
- Efficacy: 1-5.5 mg/L (some recommend 1-4 mg/L) 7, 4
- Higher targets (2-6 mg/L) for CNS infections or organisms with elevated MICs 7
- Toxicity risk increases at >5-6 mg/L 4
Check levels after 3-5 days of therapy and repeat during treatment 7, 4. Pediatric patients particularly benefit from TDM given higher pharmacokinetic variability 5.
CYP2C19 Polymorphisms
Genetic polymorphisms cause wide variability in voriconazole metabolism 2. Poor metabolizers achieve higher concentrations while ultra-rapid metabolizers may have subtherapeutic levels 2. This underscores the importance of TDM rather than relying solely on weight-based dosing.
Drug Interactions
Voriconazole has extensive drug-drug interactions as both a substrate and inhibitor of CYP450 enzymes 2. When co-administered with:
- Phenytoin or efavirenz: Increase voriconazole maintenance dose 1
- Calcineurin inhibitors (post-transplant): Voriconazole increases their levels, requiring close monitoring 8
Unique Toxicities
Voriconazole causes several distinctive adverse effects 2:
- Visual disturbances (photophobia, blurred vision) in ~30% of patients—dose-related and reversible 9
- Photosensitivity—counsel patients on sun protection
- Hepatotoxicity—monitor liver enzymes regularly
- Periostitis with prolonged use
- CNS effects (hallucinations, confusion)—associated with elevated concentrations 4
Common Pitfalls
- Forgetting to reduce maintenance dose in hepatic impairment—this is unique to voriconazole among triazoles
- Using IV formulation in severe renal dysfunction—switch to oral when CrCl <50 mL/min
- Not performing TDM—essential given high pharmacokinetic variability
- Administering oral doses with food—decreases absorption significantly
- Inadequate loading doses—particularly problematic in children who require higher mg/kg doses