Parenteral nutrition (PN) is a vital therapeutic modality for a specific group of patients in need of nutritional support. The proper use of this complex therapy is capable of maximizing its clinical benefits, minimizing the potential risks of adverse events. In certain situations, the clinical lability in which the patient finds himself requires the prescription of customized parenteral formulas. Due to the number of components used in these solutions, the possibilities of Physico-chemical incompatibilities are common and represent a serious problem. For this, prescribers must be familiar with its composition process in order to guarantee a safe formula for infusion. The objective of this work is to present the various inputs (amino acids, carbohydrates, lipids, vitamins, trace elements, electrolytes, and drugs) commonly prescribed in PN formulas, as well as their possibilities of interaction for the formation of precipitates. The concept of osmolarity and its relationship with infusion sites (central or peripheral) will also be addressed. However, an excellent understanding of the different types of inputs used in PN formulas, and also of their physical-chemical interactions capabilities, associated with good clinical judgment in the individualization of these solutions, has reduced sources of errors and ensured greater safety and quality in this type. of intervention to patients.