I suffer from COPD and chronic bronchitis. My doctor prescribed this medication and I found it VERY helpful; however, when I tried to refill my prescription, I've encountered apparent shortages among all the local pharmacies (Walgreen, CVS, Walmart, etc). Each has said that this medication is on back order and that the earliest date for possible receipt (with NO guarantees) is the end of the month. Is there a problem with the manufacturing process or in is it a problem with obtaining the ingredients required for the manufacture?