Study population: The study will include adults admitted to Internal Medicine B (IMB) department, Internal Medicine H (IMH) department or medical intensive care unit (MICU) in Rambam-Health Care Campus for moderate to severe Asthma exacerbation. The severity of the exacerbation will be based on several acceptable clinical and laboratory criteria, including breathless, alertness, pulse rate, respiratory rate, partial pressure of oxygen in arterial blood (PaO2), partial pressure of carbon dioxide in arterial blood (PaCO2), oxygen saturation, peak expiratory flow (PEF). Study protocol: The study is a prospective, randomized, double-blind, placebo-controlled, clinical trial. Patients will be randomized on admission to receive treatment with intra-venous thyroxine (100mcg once on admission and additional 100mcg after 12 hours) or placebo. The study treatment will be given only after the initial bronchodilator therapy, oxygen and informed consent are given. The primary endpoint is the time to return of the PEF rate to normal values or personal base line. PEF rates will be examined first after initial bronchodilator therapy and then, every 8 hours.
