Here is a good site that gives information about medical management.
Michigan Veterinary Specialists - Collapsing Trachea
A quote from that site:
Treatment
When treating the effects of collapsing trachea, multiple medications may be used. Medications can not reverse the changes that have occurred to the trachea, but can help make your pet more comfortable. During the acute phase, respiratory distress and severe bouts of coughing are treated with medication that relax the trachea and lung and sedate your dog.