Toxicity and therapeutic effects in mice of liposome-encapsulated nystatin for systemic fungal infections

Liposomal nystatin against experimental pulmonary aspergillosis in persistently neutropenic rabbits: efficacy, safety and non-compartmental pharmacokinetics

The activity of liposomal nystatin against invasive pulmonary aspergillosis was investigated in persistently neutropenic rabbits. Treatment groups included liposomal nystatin at dosages of 1, 2 and 4 mg/kg/day intravenously, or amphotericin B deoxycholate 1 mg/kg/day administered intravenously after normal saline loading. As compared with untreated controls, liposomal nystatin administered at 2 and 4 mg/kg/day prolonged survival and reduced fungus-mediated tissue injury and excess lung weight at post-mortem in a similar manner to amphotericin B. Although amphotericin B was superior in clearing infected lung tissue, treatment with all regimens of liposomal nystatin led to a significant reduction in pulmonary fungal tissue burden. During treatment, ultrafast CT-scan demonstrated ongoing resolution of pulmonary lesions at 2 and 4 mg/kg/day, but not at 1 mg/kg/day. With the exception of mild increases in blood urea nitrogen (BUN) and serum creatinine values during treatment at 2 and 4 mg/kg/day, which were similar to those found in amphotericin B-treated rabbits, liposomal nystatin was well tolerated. Preliminary pharmacokinetic studies in non-infected animals established linear drug disposition of liposomal nystatin in plasma over the investigated dosage range and peak plasma levels above the MIC for the test strain after multiple daily dosing for 7 days. Liposomal nystatin increased survival and provided reduced tissue injury, effective microbiological clearance and tolerable side effects in experimental pulmonary aspergillosis in persistently neutropenic rabbits, thus providing a rational basis for further investigations in clinical trials.

Comparison of in vitro antifungal activities of free and liposome-encapsulated nystatin with those of four amphotericin B formulations

The in vitro activity of a multilamellar liposomal formulation of nystatin (Nyotran) was compared with those of free nystatin and four pharmaceutical preparations of amphotericin B. MICs for 200 isolates of two Aspergillus spp., seven Candida spp., and Cryptococcus neoformans were determined by a broth microdilution adaptation of the method recommended by the National Committee for Clinical Laboratory Standards. Minimum lethal concentrations (MLCs) of the six antifungal preparations were also determined. Both nystatin formulations possessed fungistatic and fungicidal activities against the 10 species tested. Liposomal nystatin appeared to be as active as free nystatin, with MICs and MLCs that were similar to, or lower than, those of the latter. Neither formulation of nystatin was as active as amphotericin B deoxycholate (Fungizone) or amphotericin B lipid complex (Abelcet), but both were more effective than liposomal amphotericin B (AmBisome). Our results suggest that further evaluation of liposomal nystatin is justified.

Activity of liposomal nystatin against disseminated Aspergillus fumigatus infection in neutropenic mice

The purpose of this study was to examine the activity of liposomal nystatin against a disseminated Aspergillus fumigatus infection in neutropenic mice. Mice were made neutropenic with 5-fluorouracil and were administered the antifungal drug intravenously for 5 consecutive days beginning 24 h following infection. Liposomal nystatin, at doses as low as 2 mg/kg of body weight/day, protected neutropenic mice against Aspergillus-induced death in a statistically significant manner at the 50-day time point compared to either the no-treatment, the saline, or the empty-liposome group. This protection was approximately the same as that for free nystatin, a positive control. Histopathological results showed that liposomal nystatin cleared the lungs, spleen, pancreas, kidney, and liver of Aspergillus and that there was no organ damage at the day 5 time point, which was after only three doses of liposomal nystatin. Based on these results in mice, it is probable that liposomal nystatin will be effective against Aspergillus infection in humans.

Association of polyene antibiotics with sterol-free lipid membranes. II. Hydrophobic binding of nystatin to dilauroylphosphatidylcholine bilayers

Interaction of nystatin A1 with multilamellar vesicles (MLV) of dilauroylphosphatidylcholine (DLPC), observed either by adding nystatin to preformed MLV (mixtures I) or by incorporating it during the formation of vesicles (mixtures II, inner lamellas of MLV in contact with nystatin) was investigated for 0.002 < or = nystatin/DLPC = R(A) < or = 0.20, by four complementary methods. The main results were: (i) Ultraviolet absorption and circular dichroism (CD) spectra of mixtures I revealed the occurrence of a saturable association with a stoichiometry (R(A) = 0.007 +/- 0.002) constant between 3 and 33 degrees C. (ii) By differential scanning calorimetry, thermograms of the two types of mixtures were similar only when water was in great excess. In the opposite (e.g., (H2O)/(DLPC) = R(W) < or = 300), mixture II thermograms displayed two features, upshifted by about 6.5 degrees C with respect to the sharp peak observed with mixture I, resembling those obtained for pure DLPC when the low-temperature phase was the subgel phase. For this R(W), the nystatin absolute concentrations were those for which nystatin form superaggregates as revealed by the nystatin CD spectra. It is proposed that these superaggregates are excluded from the interlamellar spacings of MLV and exert a pumping action on the interlamellar water. The subsequent dehydration of the inner lamellas is thought to convert them into the subgel state. (iii) 2H-NMR spectra of sn-2-perdeuterated DLPC MLV + nystatin mixtures II, confirmed such a temperature shift of the main transition. They showed, in addition, an ordering of the aliphatic chains immediately above the transition temperature, equivalent to a bilayer thickening of 2 A.

Comparison of cellular accumulation, tissue distribution, and anti-HIV activity of free and liposomal 2',3'-dideoxycytidine

We have investigated the cellular accumulation, tissue distribution, and antihuman immunodeficiency virus activity of free dideoxycytidine (ddC) and liposomal ddC (L-ddC). We have found that L-ddC was more efficiently taken up than its free form by RAW 264.7 cells (a monocyte-macrophage cell line) (p < 0.01) while a comparable uptake was seen in U937 cells (a promonocytic cell line). In the rat, L-ddC accumulated preferentially in liver and spleen when injected intravenously (p < 0.01), and mostly in spleen when given intraperitoneally (p < 0.01). In contrast, free ddC was rapidly eliminated out of the body. Liposomal ddC showed a similar anti-HIV activity in comparison with free ddC in U937 cells. Given the fact that encapsulation of ddC in liposomes does not affect its anti-HIV activity but enhances its in vitro cellular accumulation and its in vivo distribution in reticuloendothelial system (RES) tissues, we conclude that ddC in liposomal formulation is a promising anti-HIV agent with a targeted action on the RES, which is considered a reservoir for dissemination of virus to other cells, tissues, and organs.

Systemically administered antifungal agents. A review of their clinical pharmacology and therapeutic applications

Systemic antifungal agents express great diversity in their pharmacokinetic profiles, mechanisms of action, and toxicities. Understanding the diverse pharmacokinetic properties of systemic antifungals is critical to their appropriate application. Amphotericin B, drug of choice for most invasive mycoses, has unique pharmacokinetic properties, binding initially to serum lipoproteins and redistributing from blood to tissues. Dosing recommendations are based on the specific infection and the status of the host. Lipid formulations of amphotericin B may be able to attenuate some of its toxicities. Flucytosine is a water-soluble, fluorinated pyrimidine that possesses excellent bioavailability. It is administered only in combination with amphotericin B because of frequent development of secondary drug resistance, and is associated with dose-dependent bone marrow suppression. The antifungal azoles are relatively well tolerated, have broad spectrum antifungal activity, and are fungistatic in vitro. Ketoconazole and itraconazole are highly bound to plasma proteins, are extensively metabolised by the liver, and are relatively insoluble in aqueous solution. By comparison, fluconazole is only weakly bound to serum proteins, is relatively stable to metabolic conversion, and is water soluble. Fluconazole penetrates the cerebrospinal fluid well and is approved for primary and suppressive therapy of cryptococcal meningitis in AIDS patients. The echinocandins have a narrow spectrum of antifungal activity, being effective only against Candida spp.

In vitro and in vivo evaluation of antifungal agents

The evaluation of any antifungal agent involves the determination of its in vitro and in vivo activity against pathogenic and/or opportunistic fungi. The in vitro evaluation is followed by an in vivo evaluation in animal models, and clinical trials in humans. From the first report of the efficacy of the iodides for the treatment of sporotrichosis (1903) until the introduction of the imidazoles (azoles, 1960s), the number of antifungal agents available was very limited, including griseofulvin (1939), nystatin (1950), amphotericin B (1956), and flucytosine (1964). This paper briefly reviews the status of the antifungal agents currently used, and gives a more in depth evaluation of progress during recent years in the search for new antifungal drugs. Efforts to improve the efficacy of the current antifungal agents are also reviewed.

Formulation, toxicity, and antifungal activity in vitro of liposome-encapsulated nystatin as therapeutic agent for systemic candidiasis

Multilamellar vesicles containing nystatin (NYS) were compared with vesicles containing the free drug for toxicity to erythrocytes and for antifungal activity in vitro. Liposomal nystatin was as active as free NYS was against a wide variety of yeasts and fungi. The antifungal activity against Candida albicans was maintained with different liposome compositions and without sterols. Liposome encapsulation also protected the erythrocytes from the toxicity of free NYS.