A study of the antileishmanial efficacy of sodium stibogluconate was carried out in BALB/c mice. The drug was administered to Leishmania donovani-infected animals on days 7 and 8 post-infection in one of three forms; free (40-50 mg Sbv Kg-1), liposomal, or niosomal (6.4-8.0 mg Sbv Kg-1) drug. On day 14 post-infection counts of the number of parasites present in the liver, spleen and bone marrow of treated and control animals showed that although all three drug preparations significantly reduced parasite numbers in the liver (approximately equal to 99% suppression) they had little effect on those residing in the spleen or bone marrow. The carrier forms of the drug were therefore significantly more effective than free drug in reducing liver parasite burdens. Increasing the concentration and the number of doses of free drug (maximum of 500 mg Sbv Kg-1), and reducing the size of the vesicles used to deliver the drug had a minimal effect on parasite numbers in the spleen and bone marrow. It is proposed that because of the resistance of spleen and bone marrow parasites to drug therapy, the BALB/c mouse infected with L. donovani provides an excellent model system for the study of drug delivery to these deeper tissue sites.

The antileishmanial efficacies of four proprietary amphotericin B (AmB) formulations (Fungizone, AmBisome, Abelcet, and Amphocil) and an experimental nonionic surfactant vesicle (NIV) formulation were compared in a murine model of acute visceral leishmaniasis. By a multiple-dosing regimen, groups of Leishmania donovani-infected BALB/c mice were treated (2.5 mg of AmB per kg of body weight) on days 7 to 11 postinfection with one of the AmB formulations, and parasite burdens were determined on day 18 postinfection. All of the formulations caused significant suppression parasite burdens in spleens (P < 0.01 to 0.0005) and livers (P < 0.0005) compared with those in the spleens and livers of the controls. In addition, a significant suppression of parasite burdens in bone marrow (P < 0.0005) compared to the burdens in the bone marrow of the controls was obtained for all the formulations except Abelcet, which was inactive at this site. On the basis of their overall efficacies (activity against liver, spleen, and bone marrow parasites), the formulations could be ranked as follows: Amphocil = AmBisome > AmB-NIV > Abelcet > Fungizone. On the basis of spectrophotometric measurements, AmB was shown to exist in a predominantly aggregated state in all of the formulations. Although incubation in 50% serum altered the degree of aggregation, the AmB remained predominantly aggregated, indicating that the AMB-lipid complex in all of the formulations was physically stable. The results of the study showed that antiparasitic efficacy is associated positively with the degree of AmB aggregation in the presence of serum.

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Non-ionic-surfactant vesicular (NIV) formulations of paromomycin have been tested in-vitro and in-vivo for their activity against Leishmania donovani. Production of NIV was dependent both on the surfactant used and on the concentration of paromomycin; only two of the surfactants studied formed vesicles at the highest paromomycin concentration (9 mg mL(-1)). At surfactant-lipid concentrations > or = 1.5 mM, suspensions of NIV (drug- or glucose-loaded) were cytotoxic to macrophages infected with L. donovani; high levels of nitrite were produced in cell supernatants. At surfactant-lipid concentrations < 1.5 mM, drug-loaded NIV were more effective than the same dose of free drug, in terms of the percentage of cells infected and the number of parasites/cell. At surfactant-lipid concentrations < or = 0.15 mM, drug-loaded NIV were ineffective in-vitro. In-vivo, treatment with decaethylene glycol mono n-hexadecyl ether paromomycin NIV was more effective than hexaethylene glycol mono n-hexadecyl ether paromomycin NIV, in terms of suppression of liver and spleen parasite burdens. Against liver parasites, both types of paromomycin-loaded NIV were more effective than free drug. Neither the NIV nor free forms of paromomycin caused significant suppression of bone-marrow parasites. The study shows that entrapment of paromomycin in NIV can be used to increase its antileishmanial activity in-vitro and in-vivo.

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