The safety, pharmacokinetics, and distribution in tissue of an amphotericin B (AmB)-cholesteryl sulfate colloidal dispersion (ABCD) were compared with those of micellar amphotericin B-deoxycholate (m-AmB).Dogs received 14 daily injections of ABCD (0.6 to 10 mg/kg of body weight per day) or m-AmB (0.6 mg/kg/day).Safety was evaluated by monitoring body weight, hematology, clinical chemistry, and urinalysis during the study and by microscopic examination of tissues at the time of necropsy (day 16). AmB concentrations in plasma were measured in some groups on days 1, 7, and 14 and in necropsy tissue samples. ABCD produced a spectrum of toxic effects in the kidneys, gut, and liver similar to those of m-AmB, but ABCD was eightfold safer than m-AmB. The highest tolerated dose of ABCD (5.0 mg/kg/day) produced effects similar to those of m-AmB (0.6 mg/kg/day). ABCD produced lower concentrations in plasma than an equal dose of m-AmB did. Clearances on days 7 and 14 were higher for ABCD (304 and 295 ml/h kg) than they were for m-AmB (67 and 53 ml/h-kg). Concentrations in plasma reached steady state after ABCD administration, but they increased after repeated dosing with m-AmB. Diurnal fluctuations in AmB concentrations in plasma were observed 4 to 8 h after the time of dosing. ABCD resulted in lower AmB concentrations in tissue than m-AmB did, except in the reticuloendothelial system. Up to 90% of AmB administered as ABCD was recovered from the liver and spleen on day 16. Reduced drug levels in the kidneys and gut correlated with reduced indications of toxicity in these organs after ABCD administration. Although ABCD increased concentrations of AmB in the reticuloendothelial system, increased toxicity was not observed in these organs.The ability of lipid complexes to increase the therapeutic index of amphotericin B (AmB) has been demonstrated in humans (12, 21) and animal models (2,8,17). Improved delivery of active drug to pathogenic fungi or decreased delivery to sites of toxicity in the host may explain this phenomenon, and significant differences have been observed between the pharmacokinetics and the distribution in tissue of AmB-lipid complexes and conventional micellar AmB (m-AmB) (13,19,23).AmB colloidal dispersion (ABCD), a stable colloidal complex of AmB and cholesteryl sulfate (15), has been shown to have antifungal activity similar to that of m-AmB in vivo (3a). We studied the toxicity of ABCD compared with that of m-AmB after 2 weeks of daily administration to beagles, in an attempt to relate differences in the magnitude and localization of AmB toxicities to pharmacokinetic differences between the two dosage forms. Dogs were used in these studies because the toxicology and pharmacokinetics of m-AmB have been described in this species (9,10,14 were diluted to the required concentrations with sterile 5% glucose immediately prior to administration. The particle size of reconstituted ABCD, which was measured by dynamic light scattering, was 93 ± 2.0 nm (standard deviation).Animals. Male (weight, 9.8 to 11 kg) and ...