Correlation of In Vitro Activity, Serum Levels, and In Vivo Efficacy of Posaconazole against Rhizopus microsporus in a Murine Disseminated Infection

Abstract

A broth microdilution method was used to evaluate the in vitro activities of seven antifungal agents against 15 clinical strains of Rhizopus microsporus. Amphotericin B (AMB) and posaconazole (POS) were the most active drugs. In a model of disseminated R. microsporus infection in immunosuppressed mice, we studied the efficacy of POS administered once or twice daily against four of the strains previously tested in vitro and compared it with that of liposomal AMB (LAMB). LAMB was the most effective treatment for the two strains with intermediate susceptibility to POS. For the two POS-susceptible strains, LAMB and POS at 20 mg/kg of body weight twice a day orally showed similar efficacies. The in vivo efficacy of POS administered twice a day orally correlated with the in vitro susceptibility data and the serum drug concentrations.Zygomycosis is a frequently lethal invasive infection that occurs predominantly in immunocompromised patients (4), a population with a very poor prognosis and a high mortality rate (8). The clinical manifestations include rhino-orbito-cerebral, cutaneous, pulmonary, gastrointestinal, and disseminated infections (4). In a recent study in which a large number of clinical isolates of zygomycetes from different regions of the United States were molecularly identified, it was demonstrated that Rhizopus oryzae and Rhizopus microsporus were the most common species (3). Traditionally, amphotericin B (AMB) and, more recently, its lipid formulations are the front-line agents for the treatment of zygomycosis (4). Specifically, liposomal amphotericin B (LAMB) is less nephrotoxic than AMB and has better central nervous system penetration than AMB and the other lipid formulations (21). Posaconazole (POS) is a broad-spectrum triazole antifungal with a large volume of distribution into tissues (12). This drug has shown good in vitro activity against zygomycetes (1, 2) and has been used successfully as salvage therapy in some case reports and clinical trials of disseminated zygomycosis (8,22,23). However, its effectiveness remains controversial, since in experimental studies it has shown poor activity against R. oryzae, the main species causing zygomycosis (6, 9, 17). Several in vitro studies have shown that POS also exhibits significant activity against R. microsporus, another relevant clinical species (1, 2, 11), and a few clinical (14) and experimental (6) studies seem to demonstrate in vivo efficacy as well.In this study, after confirming the significant in vitro activity of POS and AMB, we evaluated the efficacy of POS against four strains of R. microsporus in a murine model of disseminated infection. Considering that antifungal susceptibility can differ substantially among different strains of a given species, which could explain the variable percentages of success demonstrated by POS and AMB in clinical trials (8,18, 23), we tested multiple strains exhibiting various in vitro responses to obtain more-robust results. MATERIALS AND METHODSThe in vitro antifungal susceptibilities of 15 clinical strains...

Comparative Pharmacodynamics of Posaconazole in Neutropenic Murine Models of Invasive Pulmonary Aspergillosis and Mucormycosis

“…The median AUC/MIC needed to achieve stasis against all 10 A. fumigatus isolates tested in their study was 87.5, with an additional 1-log 10 decrease occurring at a median AUC/MIC of 192.6, consistent with a recommended target AUC/MIC of Ͼ100. Our work also confirms previous work suggesting that MICs are a useful predictor of posaconazole efficacy in vivo (5,(15)(16)(17)(18). PK/PD analysis is critical for establishing clinically relevant susceptibility breakpoints, especially for less commonly culturedocumented pathogens such as Aspergillus spp.…”

“…Consequently, posaconazole MICs for Mucor, Rhizopus, Absidia, and Cunninghamella spp. fall in the range of clinically achievable serum concentrations, although some isolates (3,4), especially those among Rhizopus oryzae, exhibit higher MICs (Ͼ2 mg/liter) and are less responsive to treatment in animal models (5,6). Consistent with these preclinical observations, uncontrolled retrospective case series have reported encouraging efficacy with salvage posaconazole treatment in invasive mucormycosis (7).…”

“…Similarly, Lepak and col-leagues (15) reported that a free AUC (fAUC)/MIC target of 1.09 (equivalent to an AUC/MIC of 109) was required to suppress lung fungal burden in animals infected with wild-type and Cyp51 mutant isolates of A. fumigatus. Other investigators have reported a correlation of posaconazole efficacy with average or trough posaconazole serum concentrations (5,16) and MICs in experimental mucormycosis (17,18), but data describing the relationship between posaconazole AUC/MICs and treatment effect in experimental mucormycosis are lacking.…”

Correlation between In Vitro Activity of Posaconazole and In Vivo Efficacy against Rhizopus oryzae Infection in Mice

“…In a previous experimental study with the same murine model, we also observed a lack of efficacy of PSC at 40 mg/kg given once a day (19). However, we later demonstrated that the administration of PSC twice a day was more effective than administration once a day for the treatment of infections caused by a closely related fungus of the same genus, R. microsporus (18). In that study, with the administration of PSC at 20 mg/kg BID, we obtained higher serum PSC levels (Ͼ7.5 g/ml at 3 h and Ͼ2 g/ml at 24 h after the last dose) than those achieved with the daily administration of a single dose of 40 mg/kg (Ͼ5 g/ml at 3 h and Յ1 g/ml at 24 h after the last dose).…”

“…In a previous study with mice infected with R. microsporus (18), the serum PSC levels at 40 mg/kg were similar (Ͻ1 to 2 g/ml) to those obtained with the drug administered at the recommended dosage in humans. This would suggest that PSC at this concentration is therapeutic only against those strains which show low MICs (Ͻ1 g/ml).…”