Combinations of posaconazole and tacrolimus are effective against infections with azole-resistant Aspergillus fumigatus.

BACKGROUND

Solid organ transplant recipients on immunosuppressants such as tacrolimus are at increased risk of developing pulmonary aspergillosis, a severe to deadly complication with limited treatment options, especially against azole-resistant strains. This study investigates the antifungal interaction between posaconazole and tacrolimus, prompted by a case where a liver transplant recipient on tacrolimus experienced unexpected eradication of chronic Aspergillus fumigatus colonization following posaconazole prophylaxis.

METHODS

We compared the combined antifungal activity of posaconazole and tacrolimus against azole-sensitive and resistant A. fumigatus in vitro against planktonic isolates and biofilm formation and in vivo in Galleria mellonella larvae, to evaluate the potential benefit over posaconazole monotherapy.

RESULTS

The posaconazole-tacrolimus combination demonstrated a 4-fold increase in efficacy against azole-resistant isolates and a 30-fold increase against an azole-sensitive strain, in contrast to voriconazole. Moreover, this combination enhanced antifungal activity by 4- to 15-fold against biofilm formation of azole-sensitive strains, though no synergy was observed against azole-resistant biofilms. In vivo studies in Galleria mellonella confirmed a 2- to 7-fold decrease in fungal burden of both azole-sensitive and azole-resistant strains when combining posaconazole with tacrolimus, relative to posaconazole alone.

CONCLUSION

In vitro and in vivo findings confirm that posaconazole may offer therapeutic benefits for treating A. fumigatus infections in patients receiving tacrolimus. These results warrant further confirmation in mice and exploration of their clinical implications.