Pharmacokinetic-pharmacodynamic comparison of amphotericin B (AMB) and two lipid-associated AMB preparations, liposomal AMB and AMB lipid complex, in murine candidiasis models.

It is generally accepted that the lipid formulations of amphotericin B (AMB) are not as potent as conventional AMB on a milligram-per-kilogram basis. We used a neutropenic murine disseminated candidiasis model to compare the in vivo potencies of AMB, liposomal AMB (L-AMB), and AMB lipid complex (ABLC) pharmacodynamically. The pharmacokinetics of the antifungals were examined in serum and in three organs commonly seeded in disseminated candidiasis (kidneys, liver, and lung). Both single-dose time-kill studies and multiple-dosing-regimen studies were used with each of the compounds. Determinations of the numbers of CFU in the kidneys were performed following the administration of three escalating single doses of the polyenes at various times over 48 h. The areas under the time-kill curves (AUTKs) for each dose level of the drugs were compared by analysis of variance (ANOVA). In the multiple-dosing-regimen studies with five Candida isolates, AMB, L-AMB, and ABLC were administered daily for 72 h. The organism burdens in the mouse kidneys were similarly used as the treatment end point. Additional multiple regimen-dosing-studies were performed with a single Candida albicans isolate, and the microbiologic outcomes in four internal organs (kidneys, liver, spleen, and lung) were examined at the end of therapy (48 h). The relationship between the dose and the drug exposure expressed by the pharmacokinetics of the dosing regimens in serum and organ tissue were analyzed by using a maximum-effect model. ANOVA was used to compare the drug exposures necessary to achieve the 25% effective dose (ED25), ED50, ED75, and 1 log10 killing. Comparison of AUTKs suggested that AMB was 4.3- to 5.9-fold more potent than either ABLC or L-AMB. The time-kill curves for both lipid formulations were very similar. In the multiple-dosing-regimen studies, AMB was 5.0- to 8.0-fold more potent than each of the lipid formulations against five Candida isolates in the kidneys. Similar differences in potency (5.1- to 7.2-fold) were observed in the other end organs. The difference in pharmacokinetics in serum accounted for much of the difference in potency between AMB and ABLC (ratio of serum ABLC area under the curve of effective doses to serum AMB area under the curve of effective doses, 1.2). The differences in the kinetics in the various end organs between AMB and L-AMB were better at explaining the disparate potencies at these infection sites (ratio of organ L-AMB area under the curve of effective doses to organ AMB area under the curve of effective doses, 1.1).