The cough syrup you are using is mainly used for productive cough, as it contains expectorant. So it will not reduce your cough rather will make small amount of mucus constantly and trickle your respiratory tract. It is always wiser to have a careful assessment of persisting severe dry cough before starting any antibiotic. As many a time the source is seen to be of laryngeal cardiological or serious lung pathology. So, here I would suggest to have a thorough check up with a chest x-ray, functional fibreoptic laryngoscopy etc. In the mean time you can take some effective measure to reduce cough and its annoying symptoms by steam inhalation, taking a pharyngeal soothener, a cough suppressor agent etc. Hope it will help you. With regards,