* Corresponding author: Setila Dalili, Pediatric Growth Disorders Research Center, Department of Pediatrics, School of Medicine, 17 Shahrivar Hospital, Guilan University of Medical Sciences, Rasht, Iran. Tel: +989111411463; Email: setiladalili1346@gums.ac.ir Please cite this paper as: Karambin MM, Heidarzadeh A, Norouzi H, Dalili S. New Insight into the Effect of Phototherapy on Serum Magnesium Level. Iranian Journal of Neonatology. 2017 Sep: 8(3). DOI: 10.22038/ijn.2017.20603.1233 Original Article Open Access New Insight into the Effect of Phototherapy on Serum Magnesium Level Mohammad Mahdi Karambin 1 , Abtin Heidarzadeh 2 , Hadi Norouzi 1 , Setila Dalili 1 * 1. Pediatric Growth Disorders Research Center, Department of Pediatrics, School of Medicine, 17 Shahrivar Hospital, Guilan University of Medical Sciences, Rasht, Iran 2. School of Medicine, Guilan University of Medical Sciences, Rasht, Iran ABSTRACT Background: Jaundice is one of the most common findings in the neonatal period. In almost all the cases, neonatal jaundice occurs due to the elevated level of unconjugated bilirubin. Evidence is scarce regarding the association between magnesium and bilirubin levels in neonatal hyperbilirubinemia. The present study aimed to investigate serum magnesium levels before and after phototherapy. Methods: This observational study was conducted on 65 neonates with jaundice, who were admitted to 17 Shahrivar Hospital of Rasht, Iran during September 2011-2012. Neonates with total serum bilirubin level of >20 mg/dL underwent phototherapy with 12 lamps. Magnesium levels were measured before and 24 hours after phototherapy. Data analysis was performed in SPSS version 19 using descriptive statistics (mean and standard deviation) and paired t-test at 95% confidence interval, and P-value of less than 0.05 was considered statistically significant. Results: In total, 65 neonates, including 37 boys (56.9%) and 28 girls (43.1%), were enrolled in the study. Mean magnesium level was significantly higher before phototherapy (2.07±0.33) compared to after phototherapy (1.81±0.27) (P<0.0001). Conclusion: According to the results, mean magnesium level was significantly higher before phototherapy compared to after phototherapy. However, physiological characteristics of magnesium were not assessed. It seems that the findings of the present study could lay the groundwork for further investigation in this regard. Keywords: Jaundice, Neonate, Magnesium, Phototherapy Introduction Jaundice is one of the most common manifestations in the neonatal period. Neonatal jaundice occurs due to the elevated levels of unconjugated bilirubin (UCB) (1) and may induce neurological sequelae, such as encephalopathy. Currently, the molecular mechanism of UCB that induces neurotoxicity has been elucidated incompletely (2). It seems that UCB may occur due to the affinity of bilirubin molecules to the phospholipids of the plasma membrane (3) or through activated oxidative stress and different pathways (2). Moreover, bilirubin may induce excitotoxicity mechanisms, contributing to neur- onal injuries. Bilirubin exhibits an affinity for the phospholipids of the plasma membrane, such as the N-methyl-D-aspartate (NMDA) receptors. Therefore, it seems that the activation of NMDA receptors may induce neuronal injury, which could be blocked by the antagonists of the NMDA receptors. According to the literature, magnesium is an NMDA antagonist, which could decrease the neurotoxic effects of bilirubin (4). Evidence suggests that the protective effects of antenatal MgSO4 administration in ischemic events and hypoxic brain damage are due to the increased risk of middle cerebral artery (5). Although we were not able to assess the physiological characteristics of magnesium, it seems that our findings could lay the groundwork for further investigation in this regard. The present study aimed to evaluate the total serum magnesium level in icteric neonates before and after phototherapy.