In this study, investigators will compare the efficacy and safety of intravenous (IV) Magnesium sulfate in decreasing bronchiolitis clinical severity score and the duration of hospitalization in admitted patients, as compared to placebo.

• On arrival to Pediatric Emergency Center, patients will be attended by a pediatric specialist on call who will take history and perform full physical examination. Patients will be assessed for eligibility to the study based on the inclusion criteria.
• Guardians of eligible patients will be approached with the study design, objectives and risks; Patients will be included after obtaining a verbal and assigned written consent.
• A chest radiograph and Magnesium level in serum will be requested for all study patients upon recruitment.
• The observation physician will complete the data collection sheet that will include the patient's demographics, physical examination, bronchiolitis clinical severity score,oxygen saturation, chest radiograph findings and Magnesium level.
• Treatment will be delivered to enrolled patients as currently practice in PEC(Nebulized epinephrine 1:1000 1ml in 5 ml of 5% hypertonic saline, every 4 hours until discharge, for all patients and if there is history of Bronchial Asthma in mother, father or full sibling. And/or history of Eczema in the Child ,patients will start on dexamethasone 1mg/kg orally stat.(max-10 mg/dose). Then 0,6 mg/kg orally once daily starting from second day of admission for 4 days).
• All patients will be randomized to receive either Magnesium sulfate intravenous single dose over 1 hour or placebo. And it will be given in the same time with currently practice treatment
• Epinephrine nebulization can be given on PRN basis up to a maximum of every one hour, at a dose of 0.5 mg/kg (min 2.5mg/dose and max 5 mg/dose) mixed in 5 ml of 5% hypertonic saline.•
• Bronchiolitis severity score (BSS) will be recorded at 0, 4, 8, 12, 16,20,24,36,48,60,72 hours, and on discharge.
• Vital signs will be recorded at 0, 2, 4 hours and then every 4 hours from the administration of study medication.
• All patients will be followed up for two weeks post discharge by a phone call asking about the general condition, relapse of symptoms, or need for readmission.

Inclusion Criteria:

Infants 1-18 months of age presenting to Al Saad Pediatric Emergency Center from October 2012 to May 2015 with diagnosis of Bronchiolitis and bronchiolitis clinical severity score > 4,will be include in the study.

Exclusion Criteria:

• Prematurity (Gestational age 34 weeks or less);

• Previous history of wheezing;

• Use of steroid within 48 hours of presentation;

• CRITICALLY ill patients with one or more of the following:

  1. obtunded consciousness
  2. progressive respiratory failure requiring intensive care unit (PICU) admission;
  3. history of apnea within 24 hours before presentation
  4. oxygen saturation < 85% on room air at the time of recruitment

• History of chronic lung disease;Chronic lung disease of prematurity Cystic fibrosis;

• Congenital heart disease.

• All immunodeficient children: primary or secondary

• Known hypersensitivity to magnesium sulfate.

• Known to have magnesium or calcium metabolism disturbance. (e.g.; vitamin D deficiency, hypoparathyroidism).