Software for Dosage Individualization of Voriconazole: a Prospective Clinical Study.

Voriconazole is a first-line antifungal agent. Therapeutic drug monitoring is a standard of care. The best way to adjust dosages to achieve desired drug exposure endpoints is unclear due to nonlinear and variable pharmacokinetics. Previously described software was used to prospectively adjust voriconazole dosages. The CYP2C19, CYP3A4, and CYP3A5 genotypes were determined. The primary endpoint was the proportion of patients with a Cmin at 120 h in the range 1 to 3 mg/liter using software to adjust voriconazole dosages. A total of 19 patients were enrolled, and 14 were evaluable. Of these, 12/14 (85.7%; 95% confidence interval = 57.2 to 98.2%) had a Cmin at 120 h posttreatment initiation of 1 to 3 mg/liter, which was higher than the a priori expected proportion of 33%. There was no association of CYP genotype-derived metabolizer phenotype with voriconazole AUC. Software can be used to adjust the dosages of voriconazole to achieve drug exposures that are safe and effective. (The clinical trial discussed in this paper has been registered in the European Clinical Trials Database under EudraCT no. 2013-0025878-34 and in the ISRCTN registry under no. ISRCTN83902726.).

Voriconazole pharmacokinetics following HSCT: results from the BMT CTN 0101 trial.

BACKGROUND: Voriconazole is a first-line agent for the prevention and treatment of a number of invasive fungal diseases. Relatively little is known about the relationship between drug exposure and the prevention of invasive fungal infections. PATIENTS AND METHODS: A pharmacokinetic-pharmacodynamic substudy was performed as part of the BMT CTN 0101 trial, which was a randomized clinical trial comparing voriconazole with fluconazole for the prevention of invasive fungal infections in HSCT recipients. A previously described population pharmacokinetic model was used to calculate the maximum a posteriori Bayesian estimates for 187 patients. Drug exposure in each patient was quantified in terms of the average AUC and average trough concentrations. The relationship between drug exposure and the probability of breakthrough infection was investigated using logistic regression. AUC and trough concentrations in patients with and without breakthrough infection were compared. RESULTS: Pharmacokinetic data from each patient were readily described using the maximum a posteriori Bayesian estimates. There were only five patients that had a breakthrough infection while receiving voriconazole in the first 100 days post-HSCT. For these patients, there was no statistically significant relationship between the average AUC or average trough concentration and the probability of breakthrough infection [OR (95% CI) 1.026 (0.956-1.102) and 1.108 (0.475-2.581), respectively]. P value for these estimates was 0.474 and 0.813, respectively. CONCLUSIONS: Given the very small number of proven/probable infections, it was difficult to identify any differences in drug exposure in HSCT recipients with and without breakthrough fungal infections.

Pharmacodynamics of Isavuconazole in a Dynamic In Vitro Model of Invasive Pulmonary Aspergillosis.

Isavuconazonium sulfate is a novel triazole prodrug that has been recently approved for the treatment of invasive aspergillosis by the FDA. The active moiety (isavuconazole) has a broad spectrum of activity against many pathogenic fungi. This study utilized a dynamic in vitro model of the human alveolus to describe the pharmacodynamics of isavuconazole against two wild-type and two previously defined azole-resistant isolates of Aspergillus fumigatus. A human-like concentration-time profile for isavuconazole was generated. MICs were determined using CLSI and EUCAST methodologies. Galactomannan was used as a measure of fungal burden. Target values for the area under the concentration-time curve (AUC)/MIC were calculated using a population pharmacokinetics-pharmacodynamics (PK-PD) mathematical model. Isolates with higher MICs required higher AUCs in order to achieve maximal suppression of galactomannan. The AUC/MIC targets necessary to achieve 90% probability of galactomannan suppression of <1 were 11.40 and 11.20 for EUCAST and CLSI, respectively.

Pharmacodynamics of amphotericin B deoxycholate, amphotericin B lipid complex, and liposomal amphotericin B against Aspergillus fumigatus.

Amphotericin B is a first-line agent for the treatment of invasive aspergillosis. However, relatively little is known about the pharmacodynamics of amphotericin B for invasive pulmonary aspergillosis. We studied the pharmacokinetics (PK) and pharmacodynamics (PD) of amphotericin B deoxycholate (DAMB), amphotericin B lipid complex (ABLC), and liposomal amphotericin B (LAMB) by using a neutropenic-rabbit model of invasive pulmonary aspergillosis. The study endpoints were lung weight, infarct score, and levels of circulating galactomannan and (1 → 3)-ß-D-glucan. Mathematical models were used to describe PK-PD relationships. The experimental findings were bridged to humans by Monte Carlo simulation. Each amphotericin B formulation induced a dose-dependent decline in study endpoints. Near-maximal antifungal activity was evident with DAMB at 1 mg/kg/day and ABLC and LAMB at 5 mg/kg/day. The bridging study suggested that the "average" patient receiving LAMB at 3 mg/kg/day was predicted to have complete suppression of galactomannan and (1 → 3)-ß-D-glucan levels, but 20 to 30% of the patients still had a galactomannan index of >1 and (1 → 3)-ß-D-glucan levels of >60 pg/ml. All formulations of amphotericin B induce a dose-dependent reduction in markers of lung injury and circulating fungus-related biomarkers. A clinical dosage of liposomal amphotericin B of 3 mg/kg/day is predicted to cause complete suppression of galactomannan and (1 → 3)-ß-D-glucan levels in the majority of patients.

Efficacy of an abbreviated induction regimen of amphotericin B deoxycholate for cryptococcal meningoencephalitis: 3 days of therapy is equivalent to 14 days.

UNLABELLED: Cryptococcal meningoencephalitis is an urgent global health problem. Induction regimens using 14 days of amphotericin B deoxycholate (dAmB) are considered the standard of care but may not be suitable for resource-poor settings. We investigated the efficacy of conventional and abbreviated regimens of dAmB for cryptococcal meningoencephalitis in both murine and rabbit models of cryptococcal meningoencephalitis. We examined the extent to which immunological effectors contribute to the antifungal effect. We bridged the results to humans as a first critical step to define regimens suitable for further study in clinical trials. There were significant differences in the murine plasma-versus-cerebrum dAmB concentration-time profiles. dAmB was detectable in the cerebrum throughout the experimental period, even following the administration of only three doses of 3 mg/kg. dAmB induced a fungistatic effect in the cerebrum with a 2- to 3-log10 CFU/g reduction compared with controls. The effect of 3 days of therapy was the same as that of daily therapy for 14 days. There was no evidence of increased numbers of CD3(+) CD4(+) or CD3(+) CD8(+) cells in treated mice to account for the persistent antifungal effect of an abbreviated regimen. The administration of dAmB at 1 mg/kg/day for 3 days was the same as daily therapy in rabbits. The bridging studies suggested that a human regimen of 0.7 mg/kg/day for 3 days resulted in nearly maximal antifungal activity in both the cerebrum and cerebrospinal fluid. An abbreviated regimen (3 days of therapy) of dAmB appears to be just as effective as conventional induction therapy for cryptococcal meningoencephalitis. IMPORTANCE: Cryptococcal meningitis is a significant and neglected infection that is associated with excessive morbidity and mortality. In well-resourced health care settings, induction therapy with at least 2 weeks of amphotericin B deoxycholate (dAmB) is advocated. Multiple clinical studies suggest that dAmB is the drug of choice for cryptococcal meningitis. In many parts of the world where the burden of cryptococcal meningitis is highest, it is infeasible to administer dAmB for prolonged periods. This paper provides the experimental basis for the efficacy of abbreviated regimens of dAmB for cryptococcal meningitis. The concept was explored in two well-validated laboratory animal models of cryptococcal meningitis, and the results were bridged to humans by using a range of mathematical modeling techniques. A 3-day regimen is as effective as the standard 14-day course. An abbreviated regimen is significantly more feasible and may enable better antifungal therapy to be administered to many patients with this frequently lethal disease.

In vitro susceptibility of Aspergillus fumigatus to isavuconazole: correlation with itraconazole, voriconazole, and posaconazole.

Triazoles are first-line agents for treating aspergillosis. The prevalence of azole resistance in Aspergillus fumigatus is increasing, and cross-resistance is a growing concern. In this study, the susceptibilities of 40 A. fumigatus clinical isolates were tested by using the CLSI method with amphotericin B, itraconazole, voriconazole, posaconazole, and the new triazole isavuconazole. Isavuconazole MICs were higher in strains with reduced susceptibilities to other triazoles, mirroring changes in voriconazole susceptibility. Isavuconazole MICs differed depending on the Cyp51A substitution.

Pharmacodynamics of liposomal amphotericin B and flucytosine for cryptococcal meningoencephalitis: safe and effective regimens for immunocompromised patients.

BACKGROUND: Cryptococcal meningoencephalitis is a lethal infection with relatively few therapeutic options. The optimal dosage of liposomal amphotericin B (LAmB) alone or in combination with flucytosine is not known. METHODS: A murine model of cryptococcal meningoencephalitis was used. The fungal density in the brain was determined using quantitative cultures. Pharmacokinetic-pharmacodynamic relationships were determined for LAmB and flucytosine administered alone. The effect of the combination was described using the Greco model and a mathematical model. The results were bridged to humans. RESULTS: Inoculation resulted in hematogenous dissemination and logarithmic growth within the central nervous system. There was histological evidence of multifocal infection throughout the brain. Both LAmB and flucytosine produced a dose-dependent reduction in fungal burden. The effect of the combination of agents in the brain was additive. Bridging studies suggested that a human dosage of LAmB 3 mg/kg/d resulted in a submaximal antifungal effect. Regimens of LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d all resulted in near-maximal antifungal activity. CONCLUSIONS: Potential regimens for further study in clinical trials include LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d.

Pharmacokinetics and pharmacodynamics of fluconazole for cryptococcal meningoencephalitis: implications for antifungal therapy and in vitro susceptibility breakpoints.

Fluconazole is frequently the only antifungal agent that is available for induction therapy for cryptococcal meningitis. There is relatively little understanding of the pharmacokinetics and pharmacodynamics (PK-PD) of fluconazole in this setting. PK-PD relationships were estimated with 4 clinical isolates of Cryptococcus neoformans. MICs were determined using Clinical and Laboratory Standards Institute (CLSI) methodology. A nonimmunosuppressed murine model of cryptococcal meningitis was used. Mice received two different doses of fluconazole (125 mg/kg of body weight/day and 250 mg/kg of body weight/day) orally for 9 days; a control group of mice was not given fluconazole. Fluconazole concentrations in plasma and in the cerebrum were determined using high-performance liquid chromatography (HPLC). The cryptococcal density in the brain was estimated using quantitative cultures. A mathematical model was fitted to the PK-PD data. The experimental results were extrapolated to humans (bridging study). The PK were linear. A dose-dependent decline in fungal burden was observed, with near-maximal activity evident with dosages of 250 mg/kg/day. The MIC was important for understanding the exposure-response relationships. The mean AUC/MIC ratio associated with stasis was 389. The results of the bridging study suggested that only 66.7% of patients receiving 1,200 mg/kg would achieve or exceed an AUC/MIC ratio of 389. The potential breakpoints for fluconazole against Cryptococcus neoformans follow: susceptible, ≤ 2 mg/liter; resistant, >2 mg/liter. Fluconazole may be an inferior agent for induction therapy because many patients cannot achieve the pharmacodynamic target. Clinical breakpoints are likely to be significantly lower than epidemiological cutoff values. The MIC may guide the appropriate use of fluconazole. If fluconazole is the only option for induction therapy, then the highest possible dose should be used.

Population pharmacokinetics of conventional and intermittent dosing of liposomal amphotericin B in adults: a first critical step for rational design of innovative regimens.

There is increased interest in intermittent regimen of liposomal amphotericin B, which may facilitate use in ambulatory settings. Little is known, however, about the most appropriate dosage and schedule of administration. Plasma pharmacokinetic data were acquired from 30 patients receiving liposomal amphotericin B for empirical treatment of suspected invasive fungal infection. Two cohorts were studied. The first cohort received 3 mg of liposomal amphotericin B/kg of body weight/day; the second cohort received 10 mg of liposomal amphotericin B/kg at time zero, followed by 5 mg/kg at 48 and 120 h. The levels of liposomal amphotericin B were measured by high-pressure liquid chromatography (HPLC). The pharmacokinetics were estimated by using a population methodology. Monte Carlo simulations were performed. D-optimal design was used to identify maximally informative sampling times for both conventional and intermittent regimens for future studies. A three-compartment pharmacokinetic model best described the data. The pharmacokinetics for both conventional and intermittent dosing were linear. The estimates for the mean (standard deviation) for clearance and the volume of the central compartment were 1.60 (0.85) liter/h and 20.61 (15.27) liters, respectively. Monte Carlo simulations demonstrated considerable variability in drug exposure. Bayesian estimates for clearance and volume increased in a linear manner with weight, but only the former was statistically significant (P = 0.039). D-optimal design provided maximally informative sampling times for future pharmacokinetic studies. The pharmacokinetics of a conventional and an intermittently administered high-dose regimen liposomal amphotericin B are linear. Further pharmacokinetic-pharmacodynamic preclinical and clinical studies are required to identify safe and effective intermittent regimens.

Combination of voriconazole and anidulafungin for treatment of triazole-resistant aspergillus fumigatus in an in vitro model of invasive pulmonary aspergillosis.

Voriconazole is a first-line agent for the treatment of invasive pulmonary aspergillosis. Isolates with elevated voriconazole MICs are increasingly being seen, and the optimal treatment regimen is not defined. We investigated whether the combination of voriconazole with anidulafungin may be beneficial for the treatment of A. fumigatus strains with elevated voriconazole MICs. We used an in vitro model of the human alveolus to define the exposure-response relationships for a wild-type strain (voriconazole MIC, 0.5 mg/liter) and strains with defined molecular mechanisms of triazole resistance (MICs, 4 to 16 mg/liter). All strains had anidulafungin minimum effective concentrations (MECs) of 0.0078 mg/liter. Exposure-response relationships were estimated using galactomannan as a biomarker. Concentrations of voriconazole and anidulafungin were measured using high-performance liquid chromatography (HPLC). The interaction of voriconazole and anidulafungin was described using the Greco model. Fungal growth was progressively inhibited with higher drug exposures of voriconazole. Strains with elevated voriconazole MICs required proportionally greater voriconazole exposures to achieve a comparable antifungal effect. Galactomannan concentrations were only marginally reduced by anidulafungin monotherapy. An additive effect between voriconazole and anidulafungin was apparent. In conclusion, the addition of anidulafungin does not markedly alter the exposure-response relationship of voriconazole. A rise in serum galactomannan during combination therapy with voriconazole and anidulafungin should be interpreted as treatment failure and not attributed to a paradoxical reaction related to echinocandin treatment.

Pharmacodynamics of itraconazole against Aspergillus fumigatus in an in vitro model of the human alveolus: perspectives on the treatment of triazole-resistant infection and utility of airway administration.

Itraconazole is used for the prevention and treatment of infections caused by Aspergillus fumigatus. An understanding of the pharmacodynamics of itraconazole against wild-type and triazole-resistant strains provides a basis for innovative therapeutic strategies for treatment of infections. An in vitro model of the human alveolus was used to define the pharmacodynamics of itraconazole. Galactomannan was used as a biomarker. The effect of systemic and airway administration of itraconazole was assessed, as was a combination of itraconazole administered to the airway and systemically administered 5FC. Systemically administered itraconazole against the wild type induced a concentration-dependent decline in galactomannan in the alveolar and endothelial compartments. No exposure-response relationships were apparent for the L98H, M220T, or G138C mutant. The administration of itraconazole to the airway resulted in comparable exposure-response relationships to those observed with systemic therapy. This was achieved without detectable concentrations of drug within the endothelial compartment. The airway administration of itraconazole resulted in a definite but submaximal effect in the endothelial compartment against the L98H mutant. The administration of 5FC resulted in a concentration-dependent decline in galactomannan in both the alveolar and endothelial compartments. The combination of airway administration of itraconazole and systemically administered 5FC was additive. Systemic administration of itraconazole is ineffective against Cyp51 mutants. The airway administration of itraconazole is effective for the treatment of wild-type strains and appears to have some activity against the L98H mutants. Combination with other agents, such as 5FC, may enable the attainment of near-maximal antifungal activity.

Pharmacodynamics of voriconazole in a dynamic in vitro model of invasive pulmonary aspergillosis: implications for in vitro susceptibility breakpoints.

BACKGROUND: Voriconazole is a first-line agent for the treatment of invasive pulmonary aspergillosis (IPA). There are increasing reports of Aspergillus fumigatus isolates with reduced susceptibility to voriconazole. METHODS: An in vitro dynamic model of IPA was developed that enabled simulation of human-like voriconazole pharmacokinetics. Galactomannan was used as a biomarker. The pharmacodynamics of voriconazole against wild-type and 3 resistant strains of A. fumigatus were defined. The results were bridged to humans to provide decision support for setting breakpoints for voriconazole using Clinical Laboratory Standards Institute (CLSI) and European Committee of Antimicrobial Susceptibility Testing (EUCAST) methodologies. RESULTS: Isolates with higher minimum inhibitory concentrations (MICs) required higher area under the concentration time curves (AUCs) to achieve suppression of galactomannan. Using CLSI and EUCAST methodologies, the AUC:MIC values that achieved suppression of galactomannan were 55 and 32.1, respectively. Using CLSI and EUCAST methodologies, the trough concentration:MIC values that achieved suppression of galactomannan were 1.68 and 1, respectively. Potential CLSI breakpoints for voriconazole are ≤ 0.5 mg/L for susceptible and >1 mg/L for resistant. Potential EUCAST breakpoints for voriconazole are ≤1 mg/L for susceptible and >2 mg/L for resistant. CONCLUSIONS: This dynamic model of IPA is a useful tool to address many remaining questions related to antifungal treatment of Aspergillus spp.

Differential in vivo activities of anidulafungin, caspofungin, and micafungin against Candida glabrata isolates with and without FKS resistance mutations.

We recently observed that the micafungin MICs for some Candida glabrata fks hot spot mutant isolates are less elevated than those for the other echinocandins, suggesting that the efficacy of micafungin may be differentially dependent on such mutations. Three clinical C. glabrata isolates with or without (S3) fks hot spot mutations R83 (Fks2p-S663F) and RR24 (Fks1p-S629P) and low, medium, and high echinocandin MICs, respectively, were evaluated to assess the in vivo efficacy in an immunocompetent mouse model using three doses of each echinocandin. Drug concentrations were determined in plasma and kidneys by high-performance liquid chromatography (HPLC). A pharmacokinetic-pharmacodynamic mathematical model was used to define the area under the concentration-time curve (AUC) that produced half- and near-maximal activity. Micafungin was equally efficacious against the S3 and R83 isolates. The estimates for the AUCs of each echinocandin that induced half-maximal effect (E(50)s) were 194.2 and 53.99 mg · h/liter, respectively. In contrast, the maximum effect (E(max)) for caspofungin was higher against S3 than R83, but the estimates for E(50) were similar (187.1 and 203.5 mg · h/liter, respectively). Anidulafungin failed to induce a ≥1-log reduction for any of the isolates (AUC range, 139 to 557 mg · h/liter). None of the echinocandins were efficacious in mice challenged with the RR24 isolate despite lower virulence (reduced maximal growth, prolonged lag phase, and lower kidney burden). The AUC associated with half-maximal effect was higher than the average human exposure for all drug-dose-bug combinations except micafungin and the R83 isolate. In conclusion, differences in micafungin MICs are associated with differential antifungal activities in the animal model. This study may have implications for clinical practice and echinocandin breakpoint determination, and further studies are warranted.

Anidulafungin for neonatal hematogenous Candida meningoencephalitis: identification of candidate regimens for humans using a translational pharmacological approach.

Hematogenous Candida meningoencephalitis (HCME) is a serious infection in premature neonates. Anidulafungin is an echinocandin antifungal agent with potent activity against Candida spp., but its efficacy and optimal regimens for human neonates with HCME are not known. A well-validated rabbit model of HCME was used to define pharmacokinetic-pharmacodynamic (PK-PD) relationships of anidulafungin. A mathematical model was fitted to the entire data set. The experimental data were bridged to humans. A population PK model was fitted to the data from human neonates receiving anidulafungin receiving a loading dose of 3 mg/kg, followed by 1.5 mg/kg/day. Monte Carlo simulations were performed to identify candidate anidulafungin regimens for humans. All untreated rabbits succumbed by ≤96 h postinoculation. The PK of anidulafungin was linear with dose-dependent penetration into the cerebrum. Anidulafungin exerted a rapid antifungal effect that was apparent in the first dosing interval. Near-maximal antifungal activity was observed with dosages of 10 to 20 mg/kg/day. The bridging studies suggested that the current regimen of first 3 mg/kg, followed by 1.5 mg/kg/day, is suboptimal. Higher dosages were associated with progressively greater antifungal effect. Anidulafungin is effective for the treatment of experimental HCME. Higher dosages than those currently used for clinical care are required for maximal antifungal effect.

Pharmacodynamics of echinocandins against Candida glabrata: requirement for dosage escalation to achieve maximal antifungal activity in neutropenic hosts.

Candida glabrata is a leading cause of disseminated candidiasis. The echinocandins are increasingly used as first-line agents for the treatment of patients with this syndrome, although the optimal regimen for the treatment of invasive Candida glabrata infections in neutropenic patients is not known. We studied the pharmacokinetics (PK) and pharmacodynamics (PD) of micafungin, anidulafungin, and caspofungin in a neutropenic murine model of disseminated Candida glabrata infection to gain further insight into optimal therapeutic options for patients with this syndrome. A mathematical model was fitted to the data and used to bridge the experimental results to humans. The intravenous inoculation of Candida glabrata in mice was followed by logarithmic growth throughout the experimental period (101 h). A dose-dependent decline in fungal burden was observed following the administration of 0.1 to 20 mg/kg of body weight every 24 h for all three agents. The exposure-response relationships for each drug partitioned into distinct fungistatic and fungicidal components of activity. Surprisingly, the average human drug exposures following currently licensed regimens were predicted to result in a fungistatic antifungal effect. Higher human dosages of all three echinocandins are required to induce fungicidal effects in neutropenic hosts.

Pharmacokinetics and pharmacodynamics of posaconazole for invasive pulmonary aspergillosis: clinical implications for antifungal therapy.

BACKGROUND: Posaconazole is a triazole with anti-Aspergillus activity. However, little is known about the utility of posaconazole as primary therapy for invasive pulmonary aspergillosis. METHODS: An in vitro model of the human alveolus was used to study the impact of minimum inhibitory concentrations (MIC) on exposure-response relationships. The pharmacokinetic-pharmacodynamic relationships of posaconazole were examined in an inhalational murine model of invasive pulmonary aspergillosis. A mathematical model was fitted to the entire data set. This model was then used to describe the relationship between drug exposure, quantified in terms of the area under the concentration time curve to MIC (AUC:MIC) and the observed antifungal effect. RESULTS: The posaconazole MIC was an important determinant of exposure-response relationships and accounted for a portion of the observed variance. Murine pharmacokinetics were linear for dosages 1-20 mg/kg/day. There was a dose-dependent decline in serum galactomannan concentrations, with near-maximal suppression following 20 mg/kg/day. The murine pharmacokinetic-pharmacodynamic data were well described by the mathematical model. An AUC:MIC ratio of 167 was associated with half-maximal antifungal effect. CONCLUSIONS: These results provide the experimental foundation for the selection of candidate posaconazole regimens for the primary treatment of invasive pulmonary aspergillosis in profoundly neutropenic hosts.

Pharmacokinetics and pharmacodynamics of amphotericin B deoxycholate, liposomal amphotericin B, and amphotericin B lipid complex in an in vitro model of invasive pulmonary aspergillosis.

The pharmacodynamic and pharmacokinetic (PK-PD) properties of amphotericin B (AmB) formulations against invasive pulmonary aspergillosis (IPA) are not well understood. We used an in vitro model of IPA to further elucidate the PK-PD of amphotericin B deoxycholate (DAmB), liposomal amphotericin B (LAmB) and amphotericin B lipid complex (ABLC). The pharmacokinetics of these formulations for endovascular fluid, endothelial cells, and alveolar cells were estimated. Pharmacodynamic relationships were defined by measuring concentrations of galactomannan in endovascular and alveolar compartments. Confocal microscopy was used to visualize fungal biomass. A mathematical model was used to calculate the area under the concentration-time curve (AUC) in each compartment and estimate the extent of drug penetration. The interaction of LAmB with host cells and hyphae was visualized using sulforhodamine B-labeled liposomes. The MICs for the pure compound and the three formulations were comparable (0.125 to 0.25 mg/liter). For all formulations, concentrations of AmB progressively declined in the endovascular fluid as the drug distributed into the cellular bilayer. Depending on the formulation, the AUCs for AmB were 10 to 300 times higher within the cells than within endovascular fluid. The concentrations producing a 50% maximal effect (EC50) in the endovascular compartment were 0.12, 1.03, and 4.41 mg/liter for DAmB, LAmB, and ABLC, respectively, whereas, the EC50 in the alveolar compartment were 0.17, 7.76, and 39.34 mg/liter, respectively. Confocal microscopy suggested that liposomes interacted directly with hyphae and host cells. The PK-PD relationships of the three most widely used formulations of AmB differ markedly within an in vitro lung model of IPA.