What is the best way to treat persistance cough?

Determine cause. Coughing is a symptom of a problem in your nose, throat, lungs, esophagus and rarely your heart. It can be the result of infection, irritation, allergy, or malignancy. Any cough persisting for more than two weeks should be evaluated by your primary care physician.
Depends. Depends on the cause.. Chronic coughs are often caused by post-nasal drip, asthma, or even reflux (gerd). Of course infection is always a possibility, so blood work and an x-ray may need to be done. Sometimes medications (ace-inhibitors for example) can cause a dry, nagging cough. For any blood, you may need a ct or even a bronchoscopy - a lighted camera - ma need to be used.