Introduction Drug incompatibilities are a constant problem in hospital care units. The multiplication of drugs injected simultaneously during patient therapy increases the risk of incompatibilities and can have a significant clinical impact. The purpose of this research was to characterize and analyze various parameters inducing variability in particle counting using a dynamic particle counter. Materials and methods Observations were performed on two-ports manifolds with two incompatible drugs, thus creating a quantifiable particulate charge. We analyzed the number of different-sized particles measured during the experiment as well as their cumulative distribution. The parameters studied on particle count were: position of the infusion device, environmental vibrations and total flow rate. Results Significantly higher particle counts were observed when the infusion device was in a vertical position or disturbed by vibrations. Total flow rate significantly reduced the number of particles. Conclusion This study enabled us to identify several variation factors through dynamic particle counting. These factors should be taken into account to reduce variability in results.