Theo-Dur is a type of medicine called a bronchodilator:

• It works by relaxing the muscles of the air passages causing them to widen.
  
  
• It does this by blocking special chemical reactions inside the muscle cells that control the degree of narrowing of the airways.
  
  
• It opens up the air passages of the lungs (bronchial tubes) and increases the flow of air through them.

Theophylline relieves cough, wheezing, shortness of breath and troubled breathing.