Tehran University of Medical Sciences Journal of Pharmaceutical Care 2322-4630 8 3 2020 09 28 110 115 Zinat Heidari Department of Clinical Pharmacy, Faculty of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran. Alireza Abdollahi Department of Pathology, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Hossein Khalili Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. 2020 03 10 2020 05 02 Backgrounds: Hypomagnesemia is a common electrolyte disturbance among critically ill patient which is associated with increased morbidity and mortality. In this study, correlations between serum and intra-cellular magnesium concentrations at the time of intensive care unit (ICU) admission with ICU complications and mortality were evaluated. Methods: This cross-sectional study included 70 consecutive adult patients admitted to the intensive care unit of a tertiary referral teaching hospital during a six-month period. Serum and intra-cellular magnesium levels were measured on admission. Clinical information, morbidity, and mortality were followed and recorded during ICU stay until discharge or death. Results: On admission, 37.14% of patients suffered hypomagnesemia. Low intra-cellular magnesium level was observed in 44.28% of patients. Cardiovascular complications and mortality were significantly higher in patients with lower serum and intra-cellular magnesium levels when compared to patients with normal levels (P < 0.05). There was a significant correlation between serum magnesium level on ICU admission and Acute Physiology and Chronic Health Evaluation (APACHE II) score (r = ˗0.39, P < 0.001). Conclusion: Particular attention should be reserved to possible prognostic and therapeutic consequences of magnesium depletion in critically ill patients. Magnesium deficiency was associated with a higher APACHE II score on admission, higher cardiovascular complications, and increased mortality. https://jpc.tums.ac.ir/index.php/jpc/article/view/328