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Liposomal Nystatin
Liposomal nystatin is a lipid-based polyene antifungal agent. It is composed of nystatin incorporated into liposomes containing dimyristoyl phosphotidyl choline and dimyristoyl phosphotidyl glycerol.
Aiming to reduce the systemic toxicity of nystatin, liposomal nystatin was first developed in 1987 by Lopez-Berestein et al. [1505, 2382]. It is being manufactured by Aronex Pharmaceuticals under the generic name liposomal nystatin and the trade name Nyotran™. It is in late Phase III clinical trials.
Similar to other polyene antifungal agents, nystatin binds to ergosterol in the fungal membrane. This binding disrupts osmotic integrity of the fungal membrane, resulting in leakage of intracellular potassium, magnesium, sugars, and metabolites and then cellular death. The lipid carrier of liposomal nystatin does not change this basic mode of action [1505].
When nystatin is incorporated into liposomes, its in vitro activity is maintained. Liposomal nystatin is active against a wide variety of yeasts and moulds, including Candida spp., Cryptococcus neoformans, and Aspergillus spp. [1120, 1505, 2352]. Comparison of nystatin and liposomal nystatin MICs produce variable results. Nystatin and liposomal nystatin MICs are either similar [1505] or liposomal nystatin MICs are lower [1668]. The mechanism for generation of lower liposomal nystatin MICs is not known, and some authorities feel that testing should simply be done using the parent compound alone (Nystatin).
As for amphotericin b and its lipid formulations, the in vitro susceptibility testing method for liposomal nystatin needs to be improved. Liposomal formulation enhances the activity of the drug by enabling the entrapment of the drug in reticuloendothelial sytem and delivery of it specifically to the site of infection. Thus, the ultimate enhanced activity of lipid formulation compared to the parent compound nystatin, is probably not an outcome of enhanced "in vitro" activity but rather is that of improved efficacy "in vivo". Thus, the significance of susceptibility testing for liposomal nystatin is not known. For details and current knowledge available for the method, see our discussion of susceptibility testing.
For liposomal nystatin MICs obtained for various types of fungi, see susceptibility patterns and the susceptibility database.
In clinical trials done so far, liposomal nystatin has been intravenously administered at doses of 0.25 to 4 mg/kg {$Rois, 1993 #7977$} [2436]. Typical doses are not known yet.
In contrast to nystatin, serious toxic reactions due to systemic administration of liposomal nystatin appear less likely. The most commonly encountered side effect is hypokalemia. [2436]. Nephrotoxicity also occurs, although details on the frequency of this side-effect are as yet unavailable [2436].
Liposomal nystatin is administered intravenously.
Liposomal nystatin is in late Phase III clinical trials. Data obtained so far are promising for its future use in treatment of systemic fungal infections.
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References
1120. Jessup, C. J., T. J. Wallace, and M. A. Ghannoum. 1997. Evaluation of antifungal activity of Nyotran against various pathogenic fungi. 37th Interscience Conference on Antimicrobial Agents and Chemotherapy, Abstract No.
1505. Mehta, R. T., R. L. Hopfer, L. A. Gunner, R. L. Juliano, and G. Lopez-Berestein. 1987. Formulation, toxicity, and antifungal activity in vitro of liposome-encapsulated nystatin as therapeutic agent for systemic candidiasis. Antimicrob. Agents Chemother. 31:1897-1900.
1668. Oakley, K. L., C. B. Moore, and D. W. Denning. 1999. Comparison of in vitro activity of liposomal nystatin against Aspergillus species with those of nystatin, amphotericin B (AB) deoxycholate, AB colloidal dispersion, liposomal AB, AB lipid complex, and itraconazole. Antimicrob. Agents Chemother. 43:1264-1266.
2352. Wallace, T. L., V. Paetznick, P. A. Cossum, G. Lopez-Berenstein, J. H. Rex, and E. Anaissie. 1997. Activity of liposomal nystatin against disseminated Aspergillus fumigatus infection in neutropenic mice. Antimicrob. Agents Chemother. 41:2238-2243.
2382. Wasan, K. M. 1997. Diversity of lipid-based polyene formulations and their behavior in biological systems. Eur. J. Clin. Microbiol. Infect. Dis. 16:81-92.
2436. Williams, A. H. 1999. Multicenter study to evaluate the safety and efficacy of varioius doses of liposome-encapsulated Nystatin in nonneutropenic patients with candidemia. 39th Interscience Conference on Antimicrobial Agents and Chemotherapy, Abstract No.
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