Nebulized Magnesium Sulfate and Sildenafil for Persistent Pulmonary Hypertension of Newborn

Inclusion Criteria: * Gestational age ≥ 36 weeks * Birth weight between 2.5 and 4 kg. * Post-natal age between 6 and 72 hours. * PPHN confirmed by echocardiography * Oxygenation index (OI) \> 30 on two occasions at least 15 minutes apart * Connected to Mechanical Ventilation Exclusion Criteria: * Failure to obtain informed consent * Newborns to mothers who received magnesium sulfate within 48 hours before labor. * Congenital heart diseases, other than patent ductus arteriosus and foramen ovale. * Major congenital anomalies (including congenital diaphragmatic hernia and lung hypoplasia). * Prior need for cardiopulmonary resuscitation. * Mean arterial blood pressure (MABP) \< 35 mmHg despite therapy with volume infusions and vasoactive inotropes. * Impaired kidney function. * Prior administration of pulmonary vasodilators. * Gastrointestinal intolerance or bleeding