Heated (20 min at 70°C) amphotericin B-desoxycholate (hAMB-DOC) was further characterized, as was another formulation obtained after centrifugation (60 min, 3000 ؋ g), hcAMB-DOC. Conventional AMB-DOC consisted of individual micelles (approximately 4 nm in diameter) and threadlike aggregated micelles, as revealed by cryo-transmission electron microscopy. For both hAMB-DOC and hcAMB-DOC, pleiomorphic cobweb structures were observed with a mean particle size of approximately 300 nm as determined by laser diffraction. The potent antifungal activity of AMB-DOC against Candida albicans is not reduced by heating. Effective killing of C. albicans (>99.9% within 6 h) was obtained at 0.1 mg/liter with each of the AMB formulations. For AMB-DOC, hAMB-DOC, and hcAMB-DOC, cation release ( 86 Rb ؉ ) from C. albicans of >50% was observed at 0.8, 0.4, and 0.4 mg/liter, respectively. After heating of AMB-DOC, toxicity was reduced 16-fold as determined by red blood cell (RBC) lysis. For AMB-DOC, hAMB-DOC, and hcAMB-DOC, hemolysis of >50% was observed at 6.4, 102.4, and 102.4 mg/liter, respectively. In contrast, AMB-DOC and its derivates showed similar toxicities in terms of cation release from RBC. For AMB-DOC, hAMB-DOC, and hcAMB-DOC, cation release ( 86 Rb ؉ ) of >50% was observed at 1.6, 0.8, and 0.8 mg/liter, respectively. In persistently leukopenic mice with severe invasive candidiasis, higher dosages of both hAMB-DOC and hcAMB-DOC were tolerated than those of conventional AMB-DOC (3 versus 0.8 mg/kg of body weight, respectively), resulting in significantly improved therapeutic efficacy. In conclusion, this new approach of heating AMB-DOC may be of great value for further optimizing the treatment of severe fungal infections.As the overall prognosis for immunocompromised patients with severe invasive fungal infections remains poor, there is an urgent need for therapeutic advances. Amphotericin B-desoxycholate (AMB-DOC) remains the therapy of choice for most invasive fungal infections, but its use is significantly limited by toxic side effects. Lipid formulations of AMB have been developed by the pharmaceutical industry, with the primary aim to reduce AMB's toxicity. It is now clear from a number of clinical studies that the three industrially produced AMB-lipid formulations (Abelcet, Amphocil/Amphotec, and AmBisome) are substantially less toxic than AMB-DOC (3, 10). Studies with animal models of invasive fungal infections have clearly demonstrated that often high dosages of AMB-lipid formulations are needed for treatment to be effective (5). Questions regarding the optimal dosing and duration of treatment in human patients are still unanswered for each of the AMB-lipid formulations. Therefore, and also because treatment with AMB-lipid formulations is very expensive, many patients with severe invasive fungal infections are still undergoing aggressive treatment with conventional AMB-DOC.It was recently shown by others (1, 2, 8, 9) that when AMB-DOC is heated for 20 min at 70°C (hAMB-DOC), its toxicity is greatly reduced without ...