Background and Importance Invasive aspergillosis is on the rise due to factors like increased oncological therapies, corticoid treatments, and viral infections. Managing this infection is challenging, especially with the drug voriconazole, which has a narrow therapeutic range and variable effects between individuals.

Aim and Objectives To describe serum levels of voriconazole in a cohort of patients in two tertiary-level hospitals.

Material and Methods Descriptive observational retrospective multicentre study enrolling patients who received antifungal treatment with voriconazole for the diagnosis or high suspicion of invasive aspergillosis in the period between 1January to 31 August 2023. Patients received 6mg/kg on the first day and a maintenance dose 4mg/kg/12 h. Serum levels were measured using the HPLC method at steady state, considering 1.5–5.5 mg/L as the therapeutic range. The following variables were collected: age, gender, weight.

Results 53 patients were evaluated (36, 67.9% male), all adults with a mean age ± SD 62.7 ± 9.8 years and mean weight ± SD 68.6 ± 17.3 kg, and a total of 90 determinations were carried out.

42.2% of the cases were in the therapeutic range, but the 57.8% not. Of them, 61.5% had subtherapeutic levels and 38.5% supratherapeutic.

In case of levels in therapeutic range, the same dose was maintained.

In case of levels in subtherapeutic range (mean levels ± SD 0.7 ± 2.7), doses were increased by 25–50% until therapeutic levels were achieved. If they were not reached, a switch to isavuconazole was made.

In case of levels in supratherapeutic range (7.2 ± 2.7) doses were decreased by 25–50%. In some cases, monitoring was repeated due to improper sample collection.

Conclusion and Relevance The high interindividual variability of voriconazole brings to light the need of monitoring serum levels, to adjust the dose to reach effective levels and avoid toxicity.

Conflict of Interest No conflict of interest.