Interaction between Posaconazole and Caspofungin in Concomitant Treatment of Mice with Systemic Aspergillus Infection

Abstract

The interaction of posaconazole and caspofungin was evaluated in concomitant treatment of Aspergillus fumigatus (two strains) or A. flavus (one strain) systemic infections in immunocompetent mice. Survival curves for mice treated with the combinations were compared statistically with those for mice treated with the component monotherapies. No antagonism was observed.Invasive aspergillosis continues to be a serious threat to immunocompromised patients, resulting in very significant mortality (2, 8) despite antifungal therapy (15). Outcomes could potentially be improved through the use of combination antifungal therapy (13,14).Combination treatment using antifungal agents with different mechanisms of action could potentially be synergistic against serious fungal infections. Posaconazole (POS) is a broad-spectrum antifungal triazole which recently completed phase III clinical trials (6). POS, like other triazoles, inhibits 14-demethylase activity, resulting in inhibition of the synthesis of ergosterol, a key component of fungal cell membranes. Caspofungin (CSP), an echinocandin, inhibits the synthesis of 1,3-beta-D-glucan, thereby interfering with cell wall synthesis (1). The different mechanisms of action of POS and CSP suggest that they may be complementary when used in combination. In this report, we examine the interaction between POS and CSP in combination therapy against systemic Aspergillus infections in mice.Aspergillus fumigatus ND158 and ND231 and A. flavus ND83 were obtained from the Schering-Plough Research Institute culture collection. The minimum effective concentration (MEC) end points for CSP were described by Arikan et al. (4). MICs for POS and CSP were determined and end points read according to CLSI methodology (M38-A) (10). Drug interactions between POS and CSP were determined by a checkerboard microdilution MIC method. Preparation of the inoculum, drug dilutions, and reading of end points for drug interaction tests were performed as described in document M38-A. The drug interaction studies were scored by using the azole end point (100% inhibition of growth) and, consequently, were primarily a measure of the impact of CSP on the POS MIC. The fractional inhibitory concentration (FIC) index (5) was defined as synergistic if the FIC was Յ0.5, indifferent if the FIC was Ͼ0.5 but Յ4, and antagonistic if the FIC was Ͼ4.For infection studies, A. fumigatus ND158 and ND231 were grown on Sabouraud dextrose agar slants and A. flavus ND83 was grown on malt extract agar slants for 7 days at 28°C. The conidia were washed off the slants and used to inoculate tissue culture flasks containing malt extract agar, which were incubated for 7 to 8 days at 28°C. Conidia from four flasks were suspended and diluted 1:5 in saline, and this suspension was used for infection of immunocompetent mice on day 0 by intravenous injection of 0.1 ml into the tail vein. Inocula (CFU/ mouse), determined by plate counts on Sabouraud dextrose agar, were 1.5 ϫ 10 6 and 9.5 ϫ 10 6 for ND158, 1.9 ϫ 10 6 , 4.4 ϫ 10 6 , and 4.9 ϫ 10 6 for ...

Role of Innate Immune Receptors in Paradoxical Caspofungin ActivityIn Vivoin Preclinical Aspergillosis

“…Our data confirm that the MIC/MEC values may not be good predictors for in vivo response to caspofungin, as already suggested (2,8), and indicate that monitoring markers of inflammation could be useful in the clinical evaluation of the therapeutic efficacy of CAS. Moreover, as defined TLR genetic polymorphisms are associated with susceptibility to human IA (12), the findings of the present study suggest the utility of immunogenetic screening of prospective patients to optimize CAS therapy.…”

The Strength of Synergistic Interaction between Posaconazole and Caspofungin Depends on the Underlying Azole Resistance Mechanism of Aspergillus fumigatus

“…Although a marked synergistic effect between POSA and CAS was demonstrated in previous investigations, the mechanism of this remains unclear (18,37). Our data show that the POSA MIC is a major determinant of the strength of the synergistic interaction and that this synergistic effect is concentration dependent, with strong interactions observed at concentrations of Ͻ0.5ϫ MIC.…”

“…Moreover, in vitro and in vivo studies showed synergy between POSA and CAS against A. fumigatus wild-type strains (18,19). Lepak and colleagues, however, showed that therapy using a combination of POSA and CAS (POSA/CAS) in vivo did not enhance efficacy for POSA-susceptible isolates but produced synergistic activity against two POSA-resistant isolates (20).…”

“…Moreover, in vitro and in vivo studies showed synergy between POSA and CAS against A. fumigatus wild-type strains (18,19). Lepak and colleagues, however, showed that therapy using a combination of …”

Concentration-Dependent Effects of Caspofungin on the Metabolic Activity of Aspergillus Species

“…In recent studies of caspofungin activity in mouse models of invasive aspergillosis, survival was different among groups infected with Aspergillus isolates with the same or comparable MEC values, suggesting that the MEC was not a good predictor of in vivo response to caspofungin and that other factors may play a role (4,7). Furthermore, in a study by Cacciapuoti et al (7) (28).…”