Voriconazole: an antifungal that fails high and fails low
Voriconazole has a narrow band it needs to stay inside: too low and a dangerous infection is undertreated, too high and the drug itself becomes the problem. CYP2C19 decides which way a standard dose tends to drift, and both directions have a published answer.
Also sold as: Vfend.
What voriconazole is
Voriconazole is an antifungal drug used against serious, often life-threatening fungal infections, including invasive aspergillosis and some Candida infections. It is given in hospital and continued by mouth, usually in people who are already very unwell or whose immune systems are suppressed. Because its safe and effective range is narrow, its blood level is frequently measured during treatment.
Why your genes come into it
CYP2C19 is the main enzyme clearing voriconazole, and unusually this drug has a problem at both ends of the metabolizer scale. Poor metabolizers clear it slowly, so a standard dose can climb to levels linked with liver and nervous-system toxicity. Rapid and ultrarapid metabolizers clear it quickly, so the same dose can fall below the level needed to control the infection, and a subtherapeutic antifungal in a seriously ill patient is its own emergency. That is why the guidance at both extremes leans toward a different antifungal that does not depend on CYP2C19, rather than trying to dose around a gene that is pulling the level off target from the start.
What published guidance says
The rows below restate CPIC's published guidance for each possible CYP2C19 result. They describe what a physician treating a fungal infection weighs, including when to choose a different antifungal, not a change for anyone to make alone. Voriconazole is used for infections that are dangerous if undertreated, and its dosing is guided by blood-level monitoring in hospital, so this page is background rather than an instruction.
CYP2C19
| If your CYP2C19 result is | What that means | Published CPIC guidance |
|---|---|---|
| Intermediate Metabolizer | Higher dose-adjusted trough concentrations of voriconazole compared with normal metabolizers | Per CPIC (A): "Initiate therapy with recommended standard of care dosing" |
| Likely Intermediate Metabolizer | Higher dose-adjusted trough concentrations of voriconazole compared with normal metabolizers | Per CPIC (A): "Initiate therapy with recommended standard of care dosing" |
| Likely Poor Metabolizer | Higher dose-adjusted trough concentrations of voriconazole and may increase probability of adverse events | Per CPIC (A): "Choose an alternative agent that is not dependent on CYP2C19 metabolism as primary therapy in lieu of voriconazole. Such agents include isavuconazole, liposomal amphotericin B, and posaconazole. In the event that voriconazole is considered to be the most appropriate agent, based on clinical advice, for a patient with poor metabolizer genotype, voriconazole should be administered at a preferably lower than standard dosage with careful therapeutic drug monitoring." |
| Normal Metabolizer | Normal voriconazole metabolism | Per CPIC (A): "Initiate therapy with recommended standard of care dosing" |
| Poor Metabolizer | Higher dose-adjusted trough concentrations of voriconazole and may increase probability of adverse events | Per CPIC (A): "Choose an alternative agent that is not dependent on CYP2C19 metabolism as primary therapy in lieu of voriconazole. Such agents include isavuconazole, liposomal amphotericin B, and posaconazole. In the event that voriconazole is considered to be the most appropriate agent, based on clinical advice, for a patient with poor metabolizer genotype, voriconazole should be administered at a preferably lower than standard dosage with careful therapeutic drug monitoring." |
| Rapid Metabolizer | In patients for whom a rapid metabolizer genotype (*1/*17) is identified, the probability of attainment of therapeutic concentrations is modest with standard dosing | Per CPIC (A): "Choose an alternative agent that is not dependent on CYP2C19 metabolism as primary therapy in lieu of voriconazole. Such agents include isavuconazole, liposomal amphotericin B, and posaconazole." |
| Ultrarapid Metabolizer | In patients for whom an ultrarapid metabolizer genotype (*17/*17) is identified, the probability of attainment of therapeutic voriconazole concentrations is small with standard dosing | Per CPIC (A): "Choose an alternative agent that is not dependent on CYP2C19 metabolism as primary therapy in lieu of voriconazole. Such agents include isavuconazole, liposomal amphotericin B, and posaconazole." |
Can your DNA file answer this?
CYP2C19 is one of the pharmacogenes a consumer chip file can genuinely answer, so unlike most hospital-drug pages this one connects to data you may already hold. The common reduced-function *2 and increased-function *17 alleles are single positions that consumer arrays generally carry, and Aimosti reads them from a 23andMe or AncestryDNA export. Rarer alleles are not on the array and read as reference, and where the star alleles do not resolve the result is reported as Indeterminate. In practice, though, voriconazole itself is dosed by direct blood-level monitoring during treatment, so a genotype is context for that rather than a substitute.
A genotyping chip reads only a few hundred thousand pre-selected positions, about 0.02% of your genome, chosen for common variation. It does not sequence the rest, so it cannot find the rare or novel pathogenic variants the clinical and carrier modules look for: a “no finding” from chip data means “this chip never looked”, far more so than with whole-genome sequencing. Chip data suits common-variant traits, pharmacogenomic tag SNPs, and haplogroup ancestry, not clinical or carrier screening.
Common questions
Why would fast metabolism be a problem here when it is fine for some drugs?
Because voriconazole is treating a dangerous infection, so a level that runs too low is not a minor inefficiency, it is an undertreated infection. Fast metabolizers clear the drug quickly enough that a standard dose can fall short, and for a serious fungal infection that shortfall matters as much as the toxicity risk at the slow end. That is why the guidance flags both extremes rather than only the high one.
Does the same CYP2C19 result explain my response to other drugs?
The gene is the same, but the consequence is drug-specific. A poor-metabolizer result raises voriconazole levels, weakens clopidogrel activation, and lifts exposure to some antidepressants, so the direction of the effect changes from drug to drug. That is why each drug gets its own page here rather than one shared verdict on your CYP2C19 status.
Can my 23andMe file answer this?
For the common CYP2C19 variants, usually yes, which is unusual for a hospital drug. It is worth remembering that voriconazole is dosed by measuring its blood level during treatment, so a genotype from a consumer file is useful background for a clinician rather than something that changes a live dose on its own.