Acanthamoeba is a free-living amoeba that is found ubiquitously in a range of habitats including air, water, soil, hospitals and swimming pools, etc. (Marciano and Cabral, 2003; Sifaoui et al., 2021). During its life cycle, it exhibits an active stage termed as trophozoites and a latent cyst stage (Siddiqui and Khan, 2012; Reyes-Batlle et al., 2021). When the conditions are not favorable to its existence, Acanthamoeba transform into hardy cysts form (Siddiqui and Khan, 2012; Lakhundi et al., 2017; Chiboub et al., 2021). Cysts possess a double-walled structure and exhibit minimal metabolic activity making it resistant to biocides, chlorine and various antimicrobials at physiologically relevant concentrations. Cysts can withstand harsh environments such as prolonged desiccation, severe temperatures, pH, radiation and temperatures ranging from 0 °C to 2 °C (Khan et al., 2017). As an opportunistic pathogen, Acanthamoeba has been discovered as the causal agent of Acanthamoeba keratitis (AK), a painful and sight-threatening corneal infection, and granulomatous amoebic encephalitis (GAE), an uncommon but lethal central nervous system (CNS) infection (Lorenzo-Morales et al., 2013; Grün et al., 2014; Khan et al., 2017; Castro-Artavia et al., 2017; Anwar et al., 2018; Matsui et al., 2018; Szentmáry et al., 2019; Bonini et al., 2021).

The cyst form of Acanthamoeba presents a major challenge in the successful prognosis of amoebae infections. To eradicate both trophozoites and cysts, a long-term management with various drug combinations is required (Lim et al., 2008; Mirjalali et al., 2013; Martín-Navarro et al., 2017; Shing et al., 2021), and even then persistence recurrence can occur. Several drugs cocktails like amphotericin B, fluconazole, ketoconazole, miltefosine, rifampin, sulfadiazine and trimethoprim-sulfamethoxazole have been used in treating Acanthamoeba infections (Marciano and Cabral, 2003; Carnt and Stapleton, 2016). The slow pace of development of new anti-amoebic chemotherapeutic agents with translational potential, as well as the pharmaceutical industry's unresponsiveness in developing such chemotherapies has been discouraging (Khan et al., 2017). As a result, a focused treatment approach to identify medicines that can affect Acanthamoeba viability without damaging host cells is urgently needed (Anwar et al., 2019a).

Nanotechnology is a rapidly developing technology with huge potential in a variety of fields (Singh et al., 2014; Lata et al., 2017; Wang et al., 2017; Malaekeh-Nikouei et al., 2020). Besides numerous industrial applications, great advancements are anticipated in biomedical, biotechnology, electronics, medicine, metrology, and medical technology. Moreover, nanotechnology is expected to have a significant positive influence on human health (Vishwakarma et al., 2013). Nanotechnology is now being used in the development of novel drug candidates, and it is designated as a Key Enabling Technology in the European Union (EU), capable of bringing innovate therapeutic solutions to address healthcare problems (Bleeker et al., 2013; Ossa, 2014; Tinkle et al., 2014; Pita et al., 2016). There are several challenges that can create considerable barriers to nanomaterials entering into the market, regardless of whether they are therapeutically effective including biological problems, biocompatibility, physicochemical characterization, toxicity of nanomaterials, pharmacokinetics as well as pharmacodynamics evaluation, intellectual property, processing, reproducibility and overall cost-effectiveness in contrast to present medicines in the clinical development of nanomaterials (Allen and Cullis, 2004, 2013; Zhang et al., 2008; Sawant and Torchilin, 2012; Narang et al., 2013). Nanomaterials have now evolved as inimitable antimicrobial drugs (Gupta et al., 2016; Ramalingam et al., 2016). Specifically, numerous classes of antimicrobial nanoparticles (NPs) and nanosized carriers for drug delivery have demonstrated efficacy in vitro and in in vivo models for treating infectious diseases, including antibiotic-resistant infections, and can provide better therapy than traditional drugs due to their high surface area-to-volume ratio. Metal nanoparticles have been extensively used to combat multi-drug resistant bacteria. For example, AgNPs are used in products such as cosmetics, deodorants, toothpaste, water filters and food packaging (Gharpure et al., 2020). Overall, AgNPs are considered among the most promising inorganic NPs for the treatment of bacterial infections (Natan and Banin, 2017). In recent years, magnetic NPs are used in cancer therapy to treat targeted tumors (Wu and Huang, 2017). However, there are certain drawbacks to magnetic NPs-coupled with specific pharmaceuticals, such as low drug loading capacity and poor drug release control. As a result, in order to obtain coupled features of high magnetic saturation, interaction functions on the surface and their biocompatibility, to overcome, MNPs must be pre-coated with substances that ensure their biodegradability, stability and non-toxicity in the physiological medium (Chen et al., 2011; Unsoy et al., 2014).

The use of NPs in medicine, particularly for parasitic diseases, has gained a lot of attention in recent years (Singh and Singh, 2019). NPs can be used alone or in conjunction with other agents, making medications more effective and less damaging against human cells (Van Griensven and Diro, 2019). The overall aim of this study was to synthesize, characterize the magnetic nanoparticles loaded with approved medicines and to test them for their anti-parasitic activity against the pathogenic A. castellanii of the genotype T4.