Leishmaniases are zoonotic diseases caused by parasites of the genus Leishmania with high relevance in public health worldwide. Currently, available treatments present a series of toxic effects for patients and an increment in treatment-refractory parasite strains has been recorded (OPAS, 2013). Pentavalent antimonials have been used for several decades in the treatment of visceral (VL) and cutaneous (CL) leishmaniasis and are still considered first-choice drugs, as they have a better therapeutic index than second-line drugs: amphotericin B (Amph B), pentamidine and others (Haldar et al., 2011; Oliveira et al., 2011). Still, pentavalent antimonials are often associated with high frequencies of mild to moderate adverse effects, such as musculoskeletal pain, gastrointestinal disorders, headache and anorexia, in addition to some serious ones such as cardiac, hepatic and pancreatic toxicity (Oliveira et al., 2011).

This scenario stimulates the search for new treatments, based on the development of safer formulations for currently used drugs and the assessing of drugs used to treat other diseases (repositioning), such as miltefosine and Amph B (Charlton et al., 2018; Murray, 2005). Miltefosine is an alkylphosphocholine drug with activity against cancer cells (Eibl and Unger, 1990) and various trypanosomatids (Croft et al., 1996; Konstantinov et al., 1997; Santa-Rita et al., 2000). This drug has been used as an oral drug for VL (Agrawal et al., 2006) and CL (Ware et al., 2021) treatment. Amph B, it is a polyene systemic antimycotic that is used as a second-choice drug for leishmaniasis treatment by intravenous route. Despite its high cure rates, it has some drawbacks, such as nephrotoxicity that can lead to renal failure (Cohen, 1998; Lemke et al., 2005).

Nystatin is another polyene antifungal derived from Streptomyces noursei and it is chemically related to Amph B. The primary biological target of polyene compounds is the plasma membrane of fungi and protozoa cells, potentially affecting its integrity through variable mechanisms, as the formation of pores or channels. Both nystatin and Amph B have a direct action over Leishmania spp. membrane, which is believed to be, at least in part, due to their ability to bind to ergosterol, an important sterol for these parasites (Hartsel and Bolard, 1996). Therefore, nystatin action on the plasma membrane of Leishmania spp. can compromise its integrity by the alteration of its permeability causing the extravasation of intracellular components, leading to parasite death.

The leishmanicidal activity of nystatin in solution was tested on promastigotes and amastigotes of Leishmania (Viannia) braziliensis, Leishmania (Leishmania) infantum and Leishmania (Leishmania) amazonensis, and, in the latter one, it caused morphological and physiological changes (Yamamoto et al., 2018). Other studies reported effects in promastigotes of both Leishmania (Leishmania) major (Ali et al., 1997) and Leishmania (Leishmania) donovani (Luque-Ortega et al., 2003). Furthermore, this drug was able to prevent the binding and entrance of L. (L.) donovani in J774 macrophages (Tavares et al., 2006) and was related to an increase of TNF-α levels in mice blood (Semis et al., 2012).

However, to date, no in vivo study has been performed to evaluate the leishmanicidal activity of nystatin in mouse model. Data obtained herein prove, for the first time, that cutaneous infections by L. (L.) amazonensis in BALB/c mice respond to topical treatment with nystatin cream, reducing volume of the paw and decreasing the parasite load in the footpad and in draining lymph nodes.