The prophylactic and empirical use of antifungal agents in general, and azoles and echinocandins in particular, has contributed to the emergence of strains with elevated MICs (microbiological resistance), whose clinical impact and relevance are increasingly concerning. Moreover, therapeutic failure or clinical resistance is frequently observed even in the absence of microbiological resistance.
One of the factors that may explain clinical resistance in the absence of microbiological resistance is inadequate drug exposure at the site of infection, together with the pathogen’s adaptive response to host defences or to the administered antifungal therapy.
This research line, active since 2010, aims to advance the understanding of clinical resistance in Aspergillus fumigatus infection through the study of antifungal dose–response relationships by evaluating PK/PD parameters and their role in treatment efficacy. In addition, it investigates the role of biofilms as adaptive strategies that enhance fungal resistance to antifungal agents and to host immune cells.

Exposure: Pharmacokinetics of Antifungal Agents
There is now substantial evidence that the administration of an effective antifungal agent at the appropriate dose is essential to achieve adequate drug concentrations at the site of infection. Through the development of this research line (active since 2009), our group has gained extensive expertise in the development and application of chromatographic methods (HPLC/UPLC–UV/fluorescence) for antifungal quantification, which are useful for therapeutic drug monitoring (TDM).

Techniques that allow monitoring of blood drug concentrations constitute essential tools in patient management, enabling dose optimization by determining whether drug exposure is inadequate—potentially contributing to therapeutic failure and the emergence of resistance—or, conversely, excessive, thereby increasing the risk of significant toxicity.

In addition, the application of disciplines such as pharmacogenetics to antifungal therapy is promoting personalized treatment approaches and improving the management of severe invasive fungal infections (IFIs).
The use of alternative animal models, with ethical approval and under regulatory frameworks, together with methodological advances, has facilitated the preliminary study of dose–response relationships for both established antifungal agents and newly developed compounds.

Response: Monitoring Treatment Efficacy
An aspect of major relevance in the management of severe invasive fungal infections (IFIs) is the evaluation of the efficacy of the administered therapy. This research line further explores the characterization of circulating fungal-specific biomarkers that may help distinguish infection from fungal colonization and assess the effectiveness of the established treatment.
Within this framework, our efforts have focused on the study and characterization of compounds related to fungal secondary metabolism, such as gliotoxin and its derivative bis(methylthio)gliotoxin, detected in tissue and blood samples from patients with aspergillosis and in animal models, as well as other metabolites associated with fungal virulence (e.g., fumagillin and pseurotin A).

More recently, this research line has expanded to investigate adaptive strategies such as the formation of complex biofilm structures—often multispecies in nature and involving intricate interaction mechanisms—which may explain fungal resistance to antifungal agents and host immune cells, thereby contributing to therapeutic failure (clinical resistance).