In acute and subacute toxicological studies, amphotericin B methyl ester was shown to be much less toxic than the parent antibiotic. As a single intravenous dose in mice, the methyl ester was approximately 20 times less toxic than amphotericin B. Also, the acute toxicity of the methyl ester in mice was not enhanced by the presence of chemically induced hepatic or renal damage or by the concurrent administration of amphotericin B or flucytosine. In a 1-month intraperitoneal study in rats, the methyl ester was about one-fourth as nephrotoxic as amphotericin B. In a 1-month intravenous study in dogs, the methyl ester was about one-eighth as nephrotoxic and one-fourth to one-half as hepatotoxic as the parent compound. In addition, the methyl ester, unlike amphotericin B, produced minimal renal effects, which did not increase in severity with increasing dosage. Based on the results of these studies, it is concluded that amphotericin B methyl ester has the potential for an improved therapeutic ratio in the treatment of systemic mycoses.Intravenously administered amphotericin B is the most effective agent currently available for the treatment of many systemic fungal infections. This drug is therapeutically active in a number of mycoses that, prior to its availability, were invariably fatal. The use of amphotericin B for the treatment of systemic disease, however, is associated with toxic side effects; the most common of these is nephrotoxicity. Over 80% of patients given intravenous amphotericin B develop decreased renal function and abnormal urine sediment, and it is often the degree of kidney malfunction, and not the patient's therapeutic response, that determines the duration of drug administration (1, 11).Amphotericin B methyl ester (AME) is a water-soluble derivative of amphotericin B that was developed by Mechlinski and Schaffner (8,10). Both in vitro and in vivo studies have demonstrated that AME possesses significant antifungal activity (2, 4, 5, 7). Also, based on single-dose parenteral experiments in mice and dogs, AME was shown to be much less toxic than amphotericin B (6). The initial studies were conducted with the hydrochloride salt of AME, which proved to be unstable. Subsequently, the free base of AME was found to be stable (3). This report presents toxicological data from repeat-dose studies in which AME free base was compared to amphotericin B. Results from additional single-dose tests are also summarized.MATERIALS AND METHODS Drugs. AME (batch NNO09NB) with a bioassay potency of 1,210 gg/mg was stored at -20°C. A 1% solution of the antibiotic in 0.2% ascorbic acid was prepared immediately prior to use. This procedure resulted in the formation of AME ascorbate in situ. Amphotericin B for injection, USP (Fungizone Intravenous, lots 5B530 and 5D573, E. R. Squibb and Sons, Inc., Princeton, N.J.) was reconstituted according to the manufacturer's instructions. Another antifungal compound, flucytosine (Ancobon, 250-mg capsules, lot 0005-05163, Roche Laboratories, Nutley, N.J.), was tested in a single acute ...
