Available online at www.sciencedirect.com Assessment of efficacy of antifungals in experimental models of invasive aspergillosis in an era of emerging resistance: the value of real-time quantitative PCR Seyedmojtaba Seyedmousavi 1,2 , Willem J G Melchers 1,2 , Paul E Verweij 1,2 and Johan W Mouton 1,2,3 Experimental models of invasive aspergillosis (IA) have been used to explore pharmacokinetic and pharmacodynamic (PK/ PD) properties of antifungal agents. Survival is still considered the golden standard effect measure but has the disadvantage that a large number of animals are needed to determine the dose–response relationships and PK/PD of antifungals. The feasibility of using fungal load by real-time quantitative PCR (qPCR) as an effect measure has been explored recently. The majority of studies reported convincingly demonstrate a larger dynamic range for qPCR compared to conventional assays. However interpretation and translating the results to guidance in clinical decision making need further study. It is expected that the use of qPCR will become the primary outcome measure for assessment of PK/PD relationships of antifungals in experimental models of IA. Addresses 1 Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands 2 Nijmegen Institute for Infection, Inflammation and Immunity (N4i), Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands 3 Department of Medical Microbiology and Infectious Diseases, Canisius Wilhelmina Hospital, Nijmegen, Netherlands Corresponding author: Mouton, Johan W. (jwmouton@gmail.com) Current Opinion in Pharmacology 2011, 11:486–493 This review comes from a themed issue on Anti-infectives Edited by U. Theuretzbacher and J.W. Mouton Available online 1st September 2011 1471-4892/$ – see front matter # 2011 Elsevier Ltd. All rights reserved. DOI 10.1016/j.coph.2011.08.001 Introduction Whereas invasive aspergillosis (IA) remains an infection with significant mortality and morbidity ranging from 30 to 80%, the use of clinically licensed azoles such as voriconazole and posaconazole has improved the out- come of patients [1]. However, optimizing antifungal therapy in patients still needs to be addressed. Clinical trials in humans provide valuable evidence for the use of antifungal agents, but these studies are limited due to ethics, time and cost. Experimental models of IA have become a cornerstone to explore pharmacokinetic and pharmacodynamic (PK/PD) relationships of anti- fungal agents as well as the comparative utilities of diagnostic markers. In addition, animal models allow predicting the impact of resistance on outcome for IA [2  ,3]. This is of particular importance, since resistance, in particular azole resistance in Aspergillus fumigatus is increasing [4]. In contrast to investigations evaluating the exposure– response relationships of antibacterials where colony forming units (CFU) have become the mainstay of effect measurements [5  ], the most commonly used efficacy measures for antifungals are prolongation of survival and various parameters of reduction in tissue burden [6]. However, measurements of tissue burden in IA suffer from a significant number of problems and non-culture based methods in particular qPCR, are rapidly becoming the new gold standard tool for the diagnosis, detection and evaluation of tissue burden of A. fumigatus. We here discuss applications and limitations of qPCR for assess- ment of therapeutic efficacy of antifungal agents in experimental models of IA. Benefits and limitations of conventional parameters to monitor therapeutic efficacy in IA At present survival is considered the most reliable effect measure to assess therapeutic efficacy of antifungals in IA animal models infected by both azole susceptible and resistant A. fumigatus. For example, in the recent study of Mavridou et al. in an immunocompetent non-neutropenic murine model of disseminated IA, increased MICs cor- respond with reduced in vivo efficacy [7]. Overall, there was a good relationship between the area under the concentration–time curve (AUC)/MIC ratio and survival (Figure 1). AUC/MIC was a better predictor than dose/ MIC because of the non-linear pharmacokinetics of vor- iconazole resulting in a disproportional increase in AUC by dose. Such PK/PD relationships can subsequently be used to help deducing dosing regimens and clinical break- points in humans. Although survival studies are still considered the gold standard method to assess the efficacy of antifungals in IA, it has the disadvantage that a large number of animals is needed [8]. Current Opinion in Pharmacology 2011, 11:486–493 www.sciencedirect.com