The use of silver nanoparticles (AgNP) with diameter <30 nm and negative zeta potential with powerful antibacterial and antifungal activities suitable for pharmaceutical preparations administrable to humans and/or animals on the need. In particular formulations containing AgNP with the following features are claimed and particularly preferred: an effective diameter of 18.6 ± 2.3 nm evaluated by transmission electron microscopy (TEM) a mean hydrodynamic diameter of 42.3 ± 1.2 nm evaluated by dynamic light scattering and of 40.5 ± 0.6 nm evaluated by nanoparticle tracking analyzer (NanoSight) a centrifugal density size of 17.1 ± 0.7 nm evaluated by differential centrifugal sedimentation a Z potential of -20.9 ± 3.7 mV as measured by DLS-Zeta Potential. Such nanoparticles are largely more potent, at the same concentration of Ag ions, and with greater duration of antibacterial/antifungal activity as compared to standard AgNP currently available. Furthermore, the AgNP claimed retain their antibacterial/antifungal efficacy both in aqueous and non-aqueous formulations, after freeze-drying processes they are of easy synthesis and have a scars and have a low toxicity for eukaryotic cells.
