Introduction:Ketamine is an antagonist of the N-methyl-d-aspartate receptor that intervenes in the amplification of pain signals, the development of central sensitization and tolerance to opioids.Objective: To determine the relationship of ketamine infusion for more than 72 hours with the alteration of liver function tests, in hospitalized patients with acute or chronic pain, in a high complexity center.Methods: Retrospective analytical study.Hospitalized patients were recruited, during a year of study, who received ketamine infusion for at least 72 hours for pain control, and who underwent control of liver tests, before the infusion and 72 hours after the infusion.Univariate and bivariate methods were applied using SPSSv.24software.Results: 101 patients who met the eligibility criteria were included.The median age was 52 years (IQR,.The median visual analog scale (VAS) of pain on admission and discharge was 8 (IQR, 7-9) (severe) and 2 (IQR, 1-3) (mild), respectively.The infusion time varied between 72 and 168 hours.There was no difference in hemodynamic variation during infusion.There was also no significant incidence of adverse events (6 patients had some psychiatric symptoms and 4 patients reported nausea / vomiting).Regarding liver tests, there was a statistical difference (greater after the infusion), but not clinically significant.Conclusion: The ketamine infusion added to an adequate multimodal management, achieves adequate pain control, without altering liver function tests.