Overview of the lipid formulations of amphotericin B

Invasive fungal infections have been increasingly recognized as a major cause of morbidity and mortality in the immunocompromised host. Amphotericin B has a broad spectrum and has remained the drug of choice for life-threatening invasive fungal infections. However, adverse events, particularly renal insufficiency, are limiting factors in achieving an effective dose: the prescription of amphotericin B is a compromise between toxicity and efficacy. Lipid formulations offer a better therapeutic index by circumscribing amphotericin B toxicity. Three lipid formulations are available in most countries: AmBisome, the only true liposome; Abelcet, with a ribbon-like structure; and Amphocil/Amphotec, composed of disc-like structures. All these formulations contain amphotericin B, but they differ in shape, size, reticuloendothelial clearance, C(max), AUC and visceral diffusion. The impact of these differences in pharmacokinetics and pharmacodynamics on clinical efficacy is still unclear. Efficacy has been shown in neutropenic patients with fever of unknown origin, systemic candidosis, invasive aspergillosis, cryptococcal meningitis and a variety of other difficult-to-treat mycoses, such as Fusarium or Zygomycetes infections. The effective dose may vary from one formulation to the other and is c. 3-5 mg/kg/day. All formulations are less nephrotoxic than amphotericin B. In one randomized double-blind study, AmBisome 3 or 5 mg/kg/day was less nephrotoxic and gave fewer infusion-related events than Abelcet 5 mg/kg/day. Abelcet induces fewer infusion-related side effects than Amphocil. All formulations seem at least as effective as amphotericin B. In some patients with life-threatening mycosis who failed treatment with, or were intolerant to, amphotericin B, the lipid formulations were effective. Further studies with comparable selected high-risk patients are warranted to clarify the usefulness and the indications of each of the formulations. Cost is a factor limiting prescription in many institutions, where use is often restricted to patients intolerant of, or refractory to, amphotericin B.