There is a wide intra- and inter-individual variability in sedative dose requirements in mechanically ICU patients. Patient's heterogeneity, the frequent and variable organic dysfunctions, the drug interactions and the possibility of metabolite accumulation could explain this variability. However, this fact must not justify the use of excessive doses to achieve the goals of sedation. Frequently, in the absence of a specific motive, e.g. uncontrolled pain, physicians administer progressive sedative dose increases. Probably, the absence of maximum dose recommendations has originated the case's description of severe complications, sometimes mortal, or sedative toxicity, like propofol infusion syndrome. This SEMICYUC Analgesia and Sedation Work Group recommends not administering more than 4.5 mg/kg/h of propofol or 0.25 mg/kg/h of midazolam. The need to use more than these doses should force a change in the sedative or the combined administration of both. Depending on the clinical situation or the clinical patient's evolution, the use of clonidine, haloperidol or remifentanil could be better options.