Possible mechanisms of action of the compounds injected intralesionally in the treatment of cutaneous leishmaniasis, in addition to their direct effects on the parasites.
By injecting uninfected rabbits intradermally with one of the test compounds or the isotonic saline (0.9% NaCl) used as a control, the possible mechanisms of the indirect action of some drugs used intralesionally in the treatment of human cutaneous leishmaniasis [sodium stibogluconate, 2% zinc sulphate, and hypertonic (7% NaCL) saline] were explored. The 24 injected rabbits (six for the control and six for each test compound) were followed up for 30 days, both macroscopically, with checks for erythema and increases in skin thickness, and microscopically, with the histopathological examination of sections of biopsies from the injection sites. Although the microscopy revealed inflammatory-cell infiltration, beginning with eosinophils, followed by lymphocytes and finally by the proliferation of fibroblasts, at all of the injection sites, these changes were most intense with the sodium stibogluconate and 2% zinc sulphate, less marked with the hypertonic saline, and minimal and relatively short-lived with the isotonic saline. Presumably as a result of their metal content, sodium stibogluconate and zinc sulphate each probably induce tissue damage and, subsequently, severe inflammatory changes. The antileishmanial activity of hypertonic saline, however, may be entirely attributable to its osmotic effects.