Pharmacokinetic and parasitological evaluation of the bone marrow of dogs with visceral leishmaniasis submitted to multiple dose treatment with liposome-encapsulated meglumine antimoniate

Abstract

The aim of the present study was to evaluate the impact of a multiple dose regimen of a liposomal formulation of meglumine antimoniate (LMA) on the pharmacokinetics of antimony in the bone marrow of dogs with visceral leishmaniasis and on the ability of LMA to eliminate parasites from this tissue. Dogs naturally infected with Leishmania chagasi received 4 intravenous doses of either LMA (6.5 mg antimony/kg body weight, N = 9), or empty liposomes (at the same lipid dose as LMA, N = 9) at 4-day intervals. A third group of animals was untreated (N = 8). Before each administration and at different times after treatment, bone marrow was obtained and analyzed for antimony level (LMA group) by electrothermal atomic absorption spectrometry, and for the presence of Leishmania parasites (all groups). There was a significant increase of antimony concentration from 0.76 µg/kg wet organ (4 days after the first dose) to 2.07 µg/kg (4 days after the fourth dose) and a half-life of 4 days for antimony elimination from the bone marrow. Treatment with LMA significantly reduced the number of dogs positive for parasites (with at least one amastigote per 1000 host cells) compared to controls (positive dogs 30 days after treatment: 0 of 9 in the LMA group, 3 of 9 in the group treated with empty liposomes and 3 of 8 in the untreated group). However, complete elimination of parasites was not achieved. In conclusion, the present study showed that multiple dose treatment with LMA was effective in improving antimony levels in the bone marrow of dogs with visceral leishmaniasis and in reducing the number of positive animals, even though it was not sufficient to achieve complete elimination of parasites.

Reduced Tissue Parasitic Load and Infectivity to Sand Flies in Dogs Naturally Infected by Leishmania ( Leishmania ) chagasi following Treatment with a Liposome Formulation of Meglumine Antimoniate

“…This represents a continuation of our previous work which led to the design and the pharmacokinetic characterization of a novel liposomal formulation (20,37,38 (38). The dosage and interval between the doses used in the present study were chosen from pharmacokinetic data determined previously for dogs with VL (38), indicating that high levels of Sb were maintained in the liver and spleen from 24 to 96 h following a single i.v.…”

“…To our knowledge, parasitological evaluations of dogs with VL subjected to treatment with liposome-encapsulated antimonial drug have been reported in only two previous studies (12,14,37). In the first study (12), liposome-encapsulated meglumine antimoniate was administered to mongrel dogs experimentally infected with L. donovani (12 days after infection) at doses varying from 0.01 to 0.61 mg Sb/kg/day for 1, 4, and 10 days.…”

“…Although the protocol used in the present study seems, at first sight, no more effective than that used by these investigators, the use of naturally infected dogs and the parasitological evaluation 5 months after treatment make our data much more relevant to the clinical setting. In a previous study performed by our group (14,37), meglumine antimoniate encapsulated in larger liposomes (mean diameter of 1,200 nm) has been evaluated for its efficacy in naturally infected mongrel dogs using a similar protocol (four doses of 6.5 mg Sb/kg given with 4-day intervals). Determination of the parasite load in the bone marrow aspirates of dogs 30 days after the end of treatment showed a significantly lower number of positive dogs (with at least one amastigote per 1,000 host cells) in the group treated with liposomal drug, compared to the control groups (treated with saline and empty liposomes) (37).…”

“…In a previous study performed by our group (14,37), meglumine antimoniate encapsulated in larger liposomes (mean diameter of 1,200 nm) has been evaluated for its efficacy in naturally infected mongrel dogs using a similar protocol (four doses of 6.5 mg Sb/kg given with 4-day intervals). Determination of the parasite load in the bone marrow aspirates of dogs 30 days after the end of treatment showed a significantly lower number of positive dogs (with at least one amastigote per 1,000 host cells) in the group treated with liposomal drug, compared to the control groups (treated with saline and empty liposomes) (37). On the other hand, the immunocytochemical evaluations of the spleen, 4 months after the end of treatment, and of the skin of the ear at various times (0, 30, 60, 90, and 120 days after the treatment) showed no significant difference between the groups (14).…”

“…Two liposomal formulations differing in their mean vesicle diameters were obtained (38). The large-liposome formulation (mean hydrodynamic vesicle diameter of 1,200 nm) was previously evaluated in dogs with VL (14,37). Following a multiple-dose regimen, this formulation resulted in a significantly lower number of positive dogs (compared to the group of dogs treated with empty liposomes or that of untreated dogs) but was unable to clear Leishmania parasites from the bone marrow, suggesting that this tissue may be critical for treatment with this liposomal formulation.…”