In Vitro Activity of Caspofungin Combined with Sulfamethoxazole against Clinical Isolates of Aspergillus spp

Abstract

Caspofungin (CAS) inhibits fungal cell wall synthesis. Sulfamethoxazole (SMX) inhibits folate biosynthesis and is active in vitro against Aspergillus spp. We studied the activities of the combination of CAS and SMX against 31 Aspergillus isolates and compared them with that of SMX combined with amphotericin B (AMB) or itraconazole (ITC). MICs and minimal effective concentrations (MECs) were determined by the NCCLS broth microdilution method. With MIC endpoints, the combination of SMX and CAS showed synergy or synergy to additivity against 29 of 31 isolates. With MEC endpoints, synergy to additivity was found against 12 of 31 isolates and indifference was displayed against the rest of them. SMX in combination with AMB or ITC was not truly synergistic, while synergy to additivity was found for SMX-AMB and SMX-ITC against 17 of 31 and 3 of 12 isolates, respectively. No antagonism was found with any of the drug combinations. Further analysis of the synergy of CAS and SMX was performed by detailed measurement of hyphal length by microscopy and time-dependent 2,3-bis(2-methoxy-4-nitro-5-[(sulfenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT)-based hyphal damage experiments. With MEC endpoints, the combination of CAS and SMX was characterized by a greater than 50% decrease in hyphal length compared to the hyphal lengths achieved with double the concentration of each drug alone. The XTT-based hyphal damage studies showed a statistically significant (P < 0.05) reduction in viability with CAS and SMX in combination compared to the viabilities achieved with double the concentration of each drug alone. These findings support the synergy results found by using MIC endpoints and suggest that visual MEC measurements may not be sufficient to identify the synergistic interactions seen by more sensitive, quantitative methods. Animal models are required to validate the significance of the synergy of CAS and SMX against Aspergillus spp. observed in vitro.Invasive aspergillosis is one of the most common invasive fungal infections in immunocompromised patients and carries high mortality rates (10).Current therapeutic agents such as amphotericin B (AMB) and its liposomal formulations, azoles such as itraconazole (ITC) and voriconazole (VRC), and echinocandins such as caspofungin (CAS) are only partially effective for the treatment of this disease; therefore, more effective drugs and drug combinations are needed (8).Sulfamethoxazole (SMX) is an antimicrobial drug which inhibits the biosynthesis of folates (4, 6). SMX is moderately active in vitro against Aspergillus spp. (2), and Aspergillus fumigatus mutants defective in the folate biosynthesis pathway are avirulent (5). SMX is frequently administered in combination with trimethoprim to immunocompromised patients for prophylaxis for Pneumocystis carinii pneumonia (PCP). Interestingly, PCP prophylaxis in AIDS patients is associated with a decreased probability of development of invasive aspergillosis (1).We examined whether the combination of SMX with AMB, ITC, or CAS in vitro exerts ...

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

“…in the presence of caspofungin (26,28,29). These studies, however, did not aim at a comprehensive description of the concentration-dependent effects of caspofungin on the metabolic activity of this organism, and consequently the number of isolates for which the assay was performed was limited (six isolates for all three studies).…”

“…Furthermore, the MEC is an endpoint that is based upon qualitative assessment of hyphal morphology and, as such, it does not provide quantification of caspofungin activity at different concentrations. For example, using the MEC as an endpoint may be problematic for in vitro antifungal combination studies, in which the detection of significant drug interactions may require the use of more sensitive, quantitative methods that could demonstrate a concentration-effect relationship for caspofungin activity against this organism (29). Thus, in order to better understand the in vitro activity of caspofungin against Aspergillus spp.…”

Cotrimoxazole enhances the in vitro susceptibility of Coccidioides posadasii to antifungals

“…In this study, we tried to perform the susceptibility tests with yeast nitrogen base, as suggested by Hanafy et al (2007), but unfortunately this medium did not support the growth of C. posadasii (data not shown). Because other studies have already been performed with RPMI (Yekutiel et al 2004, Navarro-Martinez et al 2006, we decided to evaluate this medium in our experiments. However, we assumed that in PABA-free medium, SMX/ TMP may cause a greater reduction in AMB MICs.…”

Riboflavin and pantothenic acid biosynthesis are crucial for iron homeostasis and virulence in the pathogenic mold Aspergillus fumigatus

“…Deletion of pabA , encoding PABA synthase, catalysing an early step in folate biosynthesis, abrogated virulence in infected mice, designating this pathway as an excellent candidate for the development of novel antifungals [33]. Antibacterial sulfa drugs that inhibit dihydropteroate synthase in the folic acid biosynthetic pathway already exist and show weak antifungal activity [34]. Recent efforts have focused on developing antifungals to target other enzymes in this pathway [35].…”