Thanks for writing your query.
After reading your post, it seems that your father is having cough due to bronchoconstriction
i.e. narrowing of air passage. It can be due to an allergic reaction
You should try to find out the allergen, if any and try to avoid it.
Antihistamines along with bronchodilators will be helpful in decreasing your symptoms.
is a steroid and helps in curing bronchoconstriction but it has many side effects so oral intake should be limited and the dose should be gradually taperd down.
acts as a bronchodilator.
Safest mode of treatment for bronchitis is through inhaler route.
In this the medicine required (bronchodilator or steroid) goes directly into the air passage with minimal side efects.
Antihistaminic like Fenofexadine
120 mg can be taken once a day after discussing with your doctor.
You should follow your doctor's advice as he has examined your father and knows best about the patient.
I hope this is helpful to you.