Hello Medrol is a steroid and symptomatically it is effective against bronchitis , but you also took azithromycin and got relief . But symptoms returns and you are sensitive to penicillins and bactrim . So your doctor prescribed NITROFURANTOIN i.e. mcrobid ( you think this is only for UTI ) but this also effective against Gram +ve and Gram -ve bacteria . While in most of cases gram +ve or Gram -ve bacteria are usually causing bronchitis , so your doctor advise you macrobid. But this is equally effective also for UTI cases . But in my opinion you are having allergic bronchitis , so in such cases I advise my patient to take montelukast+ fexofenadine ,once or twice in day with antibiotics. If breathlessness also present I advise to take montelukast+ bambuterol once or twice in day and my patient respond very well . Hope this will help you. Good luck.