Hi, Macrobid contains nitrofurantoin which is used to treat bladder infections or cystitis. infections of urinary tract caused by Enterococcus, Klebsiella staphyloccuss aureus or E.coli, pneumonia, bronchitis, ear infections, infections of the skin etc. It works by stopping the growth of bacteria. This antibiotic treats only bacterial infections. The most common symptoms of immediate reactions occur between half an hour and an hour after consuming the medication. The delayed reaction which can happen after the entire series of antibiotic has been consumed. Sign of a delayed type of allergic reactions caused by Macrobid are rashes, hives, itching, red, swollen blistered or peeling skin with or without fever, wheezing, tightness in the chest or throat, trouble breathing, swallowing or talking unusual hoarseness or swelling of mouth, face, lips, throat, eyes etc. Antihistamines and corticosteroids are the best of choice here. If these allergic reactions persist for long or bother you then you should consult your doctor promptly for medical help. Tak care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician