Thanks for asking at Healthcare Magic. I read your question and I understand your concern. Respiratory tract infections are commonly caused by sretptococcus bacteria, H. Influenza, Morrhaxiella cataralis etc. These needs gram positive and gram negative coverage. Ciprofloxacin has only gram negative coverage and pseudomonas while Doxycycline has little both coverages but there is resistant in most areas of the world to these antibiotics. Metronidazole has anaerobic coverage and is useful only in lung abcess and aspirations pneumonia. I would suggest you that first it to be bacterial rather than viral. If it s bacterial then take antibiotic from penicillin or cepalosporin group. Doxycycline can be helpful. Hope it helps best. Don t forget to rate this answer. Take your best care. I will be glad to have your follow-up. Regards Dr Ejaz