Some medications frequently employed in anesthesiology and in intensive care practice may undergo reactions linked to chemical and physical characteristics when they are used with many other medications or in sequential administration and may cause precipitation. Ertapenem, tigecycline, colistin, daptomycin, vancomycin and teicoplanin are important antibiotics, some newly entering use, employed in intensive care for infections by resistant microorganisms. The compatibility of ertapenem, tigecycline, colistin, daptomycin, vancomycin and teicoplanin was researched with all medications used in our surgery using the lam-lamellar technique and visual investigations. Our study determined the precipitation characteristics of ertapenem (20 mg/mL), tigecycline (10 mg/mL), colistin (75 mg/mL), daptomycin (50 mg/mL), vancomycin (10 mg/mL) and teicoplanin (60 mg/mL). With this aim 0.1 mL of each medication was mixed on a slide with the same volume of test drug and the precipitation or the lack of each one was observed through a magnifier. Ertapenem reacted with dobutamine, verapamil, protamine, mannitol and midazolam; tigecycline reacted with diclophenac sodium and thiopental; colistin reacted with amiodorone, dobutamine, ketamine, chlorphenoxamine, protamine and ranitidine; daptomycin reacted with protamine, thiopental and dobutamine; vancomycin reacted with diclophenac sodium, gelofucine, dexketoprofen, daptomycin, ertapenem, furosemide, prednisolone, tenoxycam, dexamethasone, heparin, thiopental and bicarbonate while teicoplanin reacted with dobutamine, atracurium, ketamine, chlorphenoxamine and diltiazem under in vitro conditions causing precipitation. The in vitro reactions and precipitations observed in our study may be described as the "tip of the iceberg" of medication interactions. Future studies should determine the factors involved in the in vitro precipitations observed in our study and also the characteristic properties of these reactions.