 In patients whose disease progression is associated with inadequate voriconazole VOR drug levels, serum drug level determination can allow for dose adjustment, thereby preventing disease progression. Patients who are extensive metabolizers may have subtherapeutic VOR levels leading to treatment failure whereas, poor metabolizers may have high drug levels that cause toxicity. Isoenzyme such as CYP2C19 exhibits genetic polymorphism. Genotyping tests can also be helpful in determining patient risk subjecting to extreme spectrum of drug levels. 