Case Report Tolvaptan Response in a Hyponatremic Newborn with Syndrome of Inappropriate Secretion of Antidiuretic Hormone Cengiz Zeybek , 1 Ali Dinç Bozat , 2 Erhan Calisici , 2 Ahmet Bolat , 3 and Belma Saygili Karagol 2 1 UniversityofHealthSciences,GulhaneSchoolofMedicine,DepartmentofPediatrics,DivisionofPediatricNephrology,Ankara, Turkey 2 UniversityofHealthSciences,GulhaneSchoolofMedicine,DepartmentofPediatrics,DivisionofNeonatology,Ankara,Turkey 3 University of Health Sciences, Gulhane School of Medicine, Department of Pediatrics, Ankara, Turkey Correspondence should be addressed to Cengiz Zeybek; zeybekcengiz@yahoo.com Received 13 March 2021; Accepted 7 May 2021; Published 13 May 2021 Academic Editor: Carmelo Romeo Copyright©2021CengizZeybeketal.isisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e use of tolvaptan to treat both euvolemic and hypervolemic hyponatremia has rapidly increased in recent years. However, data on its effects on children, especially newborns and infants, are limited. Here, we present a newborn who developed syndrome of inappropriate secretion of antidiuretic hormone following an intracranial hematoma drainage operation who was unresponsive to conventional treatments. e infant was successfully treated with tolvaptan, a competitive inhibitor of the vasopressin V2 receptor. 1. Introduction Antidiuretic hormone (ADH) is produced in the hypo- thalamus and released from the posterior pituitary gland [1]. Normally, ADH is released under conditions such as hyperosmolality or hypotension, but pathological release occurs in euvolemic conditions such as syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and in hypervolemic conditions such as con- gestiveheartfailure(CHF)andnephroticsyndrome(NS). SIADH can be triggered by pain, stress, numerous medications, and brain malformations; it also occurs in association with brain injury. e first-line treatment for SIADH is fluid restriction. Other treatment options in- clude furosemide and sodium supplementation [2]. Data on the treatment outcomes of tolvaptan in children, where this drug specifically antagonizes AVPR2 recep- tors, are limited, especially for newborns. Here, we present a newborn infant who developed SIADH due to an intracranial hematoma operation and did not respond to conventional treatments but responded dramatically to tolvaptan treatment. 2. Case Report Ourfemalepatientwasbornasatwinat34weeksand5days, via C-section, to a 19-year-old mother (G1P1). Her birth weight was 1,900g (10–25 th percentile), and the head cir- cumference was 32 cm (50–75 th percentile). She was born at another center, where she was followed for 5 days, diagnosed with of prematurity and oligohydramnios, and discharged without complications. She was admitted to the neonatal intensive care unit of our hospital with complaints of vomiting and neonatal convulsion on postnatal day 27. When hospitalized, her weight was 2,160 g, and blood gas analysis revealed that serum electrolytes (sodium: 136 mmol/L), glucose, calcium, magnesium, and other biochemical values were within normal limits. Transfontanel ultrasonography performed due to convulsions revealed a hematoma in the right lateral ventricle compressing the third ventricle and grade 3 in- traventricular hemorrhage. e hematoma was drained, and an extraventricular drainage system was placed. After the operation, convulsions recurred, and the serum sodium level was 123mmol/L. Convulsions were controlled with Hindawi Case Reports in Pediatrics Volume 2021, Article ID 9920817, 4 pages https://doi.org/10.1155/2021/9920817