Background: Deposition of bilirubin in neurons causes permanent neuronal injury. Bilirubin exhibits an affinity for the phospholipids of plasma membrane like N-methyl-D-aspartate (NMDA) receptors. Magnesium is an NMDA antagonist and it acts against the neurotoxic effects of bilirubin. We compared pre- and post-phototherapy serum magnesium level of neonates with hyperbilirubinemia to find the best time of discharge and evaluate new management techniques such as magnesium supplementation.

Methods: In this semi-experimental study, we evaluated neonates admitted in Ali Asghar Children's Hospital in Tehran, Iran with signs of icter from 2009 to 2010. The inclusion criteria included age less than four weeks, no history of magnesium sulfate administration in the mother and absence of sepsis.

Results: From 106 patients with icter, 50.9% were male and 49.1% were female neonates. Their mean gestational age was 37.341.286 (33-41) weeks and the mean birth weight was 3172.12436.936 (2022-4300) grams. The frequency of underlying causes of hyperbillirubinemia included: ABO mismatch 9.34%, Rh incompatibility 4.7%, breastfeeding 16% and breast milk 44.3%. There was a significant difference (P≤0.001) between serum magnesium levels before (2.24mg/dl) and after phototherapy (2.12mg/dl). There were no significant differences between serum magnesium values in the two sexes (male=2.28, female=2.19), among different gestational age groups (<34 wks=2.35, 35-37 wks=2.27, >38 wks=2.17), between different birth weight groups (1500-2500 g=2.4 and >2500 g=2.23) or severity of hyperbilirubinemia (mild=2.23, moderate=2.21 and severe=2.29).

Conclusion: Phototherapy decreases the total magnesium concentration and magnesium administration will prevent bilirubin neurotoxicity in icteric neonates.