You should not combine it with diflucan sinus and bronchitis infection medications. Promethazine DM syrup is a drug that contains an antihistamine and a cough suppressant, while diflucan is a medication with antifungal action. It is advisable to get a prescriber's advice before taking any medicine and follow their patient care course accordingly. For sinus infection and bronchitis, turning to a pulmonologist or an ENT specialist is recommended.